MotorControlStandards

ElectroStores

----------MOTOR CONTROL STANDARDS---------

Motor isolation

SANS 6.16.5.1.5
Each motor shall be supplied by a manually operated disconnector or any other manually operated disconnecting arrangement such as a with drawable circuit-breaker, a removable link, a fuse or by the removal of a plug from a socket-outlet, which provides at least the same isolating distance, for the sake of safety, as a disconnector that is Amdt 3 a) readily accessible and mounted on or next to the motor, or b) visible from the motor, or c) lockable in the open position, or d) housed in a lockable enclosure other than a distribution board.
7.4.4.6 All electric motors shall be provided with an effective means of isolation of all poles and such means shall be adjacent to the motor.
7.8.8 Motors All electric motors shall be provided with an effective means of isolation of all poles and such means shall be adjacent to the motor. Any motor which is automatically or remotely controlled and which is not continuously supervised shall be fitted with a manually reset protective device to protect the motor from excessive temperatures.

;;;

Remote motor control

IEC 60364:
- 4.3.2.3.7 Motors which are automatically or remotely controlled, or which are not continuously supervised, shall be protected against excessive temperature rise by temperature responsive devices, unless specifically designed to be inherently heat-limiting.

Wow, I did not know the code stipulates under voltage protection required?

SANS 6.16.5.3	IEC
Motor starters Except in the case of direct-on-line starting, a starter shall have an undervoltage release that opens the circuit if the supply voltage drops sufficiently to cause the motor to stop. When the supply voltage is restored to a value that would cause the motor to restart, and unexpected restarting could cause injury to the operator of the motor, the starter shall have a means of preventing the motor from restarting, whatever the type of starter.

...

How I understand motor protection / circuit breakers graphs:-

Adjustable, current dependant time-delayed over current release protects against thermal overloading.

The ambient air temperature compensation and a precise calibration of the over current release mechanism assures an exact and reliable tripping. Often a differential release for the protection against the loss of a phase is integrated in the device.

After the interruption of a short-circuit, the tripping characteristic must not alter without any outwardly visible indication.

Fig. 1.4-3: Tripping curve of a circuit breaker with motor protective characteristics.

The grey line indicates the current form of a normal motor. After the rated speed is reached (here after about 1.5s), the starting current (6 x In) reduces to the rated current of the motor(1xIn).
a) Time-current characteristic of the bimetallic release
b) Time-current characteristic of the magnetic release
c) Characteristic of the motor

@ 90kW the Iflc=160Amp which is exactly the MCCB size.

A starting motor pulls unpredictable amount of current and truth is it is much worse with a star delta - this is probably why the MCCB trips.

Assuming there is nothing wrong with the delta circuitry /motor side it seems this application already goes into overload even during the star time (which could pull 3 or 4 x FLC - then it will trip between 5-11 or 3-10sec)

It gets worse because the MCCB is supposed to be matched according to coordination tables first (kA rating) to ensure it does not explode under fault conditions and then one rates it according to the installation.

I would do one more test and that is to start the motor without any load to confirm it is indeed not a plant/load/circuitry problem.

The HEG250U is a much better solution [160 to 250Amp adjustable] and Starting current adjust up to 13 x In.

Motor starters according to the standards is no easy task especially if integrated in a DB so rather keep it separate. (Sans reference)

6.6.7.1 Motor control that forms an integral part of a distribution board is deemed part of the fixed electrical installation and shall comply with the requirements of SANS 1973-1 or SANS 1973-3 or SANS 1973-8 or SANS 1473-1 or SANS 1765.

6.6.7.2 Components for motor control as listed in table 6.25 shall comply with the standards as given in table 4.2.

This referred to Table 4.2 covers 10 different standard sections.

"Circuit breaker overload protection for motors"

"Circuit breaker overload protection for motors" - this is way too confusing.

What does the standards say about motor protection for overload specifically with the objective to ascertain if a "normal" circuit breaker comply?

_{I am amazed at how different the NEC is to the
IEC...Many days of research for the NEC - is exhaustive!}

_{This is my version it must be read with
limitations since we don't intend re-interpreting the code but ONLY focus on
the topic at hand.}

NEC (NFPA 70 - 2011)

IEC 60947-4-1 : 2000

About motor protection

430.83: (2) Circuit Breaker. A branch-circuit inverse time circuit breaker rated in amperes shall be permitted as a controller for all motors.

Where this circuit breaker is also used for overload protection, it shall conform to the appropriate provisions of this article governing overload protection.Wow, that's a surprise

430.83:(3) Molded Case Switch. A molded case switch rated in amperes shall be permitted as a controller for all motors. And there it is!

This part of code I found most confusing so I tried to put the text in such a way that makes sense - at least to me...this is a work in progress.

8.2.5 Co-ordination with short-circuit protective devices
8.2.5.1 Performance under short-circuit conditions (rated conditional short-circuit current)
The rated conditional short-circuit current of contactors and starters backed up by short-circuit protective device(s) (SCPD(s)), combination starters and protected starters shall be verified by short-circuit tests as specified in 9.3.4. These tests are mandatory:

a) at the appropriate value of prospective current shown in table 12 (test current "r"),

and

b) at the rated conditional short-circuit current Iq if higher than test current "r".

The rating of the SCPD shall be adequate for any given rated operational current, rated operational voltage and the corresponding utilization category.

First lets cover underlying component tests:

8.2.4.1 Making and breaking capacities test:
Contactors or starters shall be capable of making and breaking currents without failure under
the conditions stated In table 7 for the required utilization categories and the number of
operations indicated, as specified in 9.3.3.5.

9.3.3.5.5 Rated making and breaking capacities
If the contactor in a starter has separately satisfied the requirements of item

a) hereafter for the utilization category of the starter, the starter need not be tested.

a) Rated making and breaking capacities of contactors
The contactor shall make and break the current corresponding to its utilization category
and for the number of operating cycles given in table 7.
See also item d) hereafter for reversing contactors.
Contactors of utilization categories AC-3 and AC-4 shall be subjected to 50 rnaking only
operations followed by 50 making and breaking operations.

d) Rated making and breaking capacities of direct-on-Iine and reversing starters(AC-4)

The starters shall make and break the currents given in table 7.

The 50 making only operations shall be done first, the current being broken by a separate
switching device, followed by the 50 making and breaking operations.
The load circuit shall be connected to the starter as would be the windings of a motor.
For starters incorporating two contactors, two contactors A and S shall be used and wired
as in normal application.

Each sequence of the 50 operations shall be:
close A - open A - close S -
open S - off period
The change-over from "open A" to "close S" shall be made as fast as the normal control system will allow.
Mechanical OR electrical interlocking means provided in the starter or available for associating contactors as reversing devices shall be used.
If the reversing circuit arrangement is such that both contactors can be energized simultaneously, ten additional sequences shall be conducted with both contactors energized simultaneously.

The off·time and on-time values given in tables 7 and 7a shall not be exceeded.

Table 7

9.3.3.6: If the contactor in a starter has separately satisfied the requirements of 9.3.3.6.1 for the utilization category of the starter, the starter need not be tested.

9.3.3.6.1 Conventional operational performance of contactors

The contactor shall make and break the current corresponding to its utilization category and
for the number of operating cycles given in table 8. See also 9.3.3.6.4.

9.3.3.6.4: The starter shall make and break the current corresponding to its utilization category

for the number of operating cycles given in table 8.
The test procedure shall be as stated in 9.3.3.5.5, item (c), except that the 50 making only
operations are not done.
pg: 53

Table 8

9.3.4 Performance under short-circuit conditions:

9.3.4.1.6 Test procedure

9.3.4.2.1: Test at the prospective current "r"
The tests shall be so conducted that conditions of maximum Ie and of maximum Ue for utilization category AC-3 are covered.

The following sequence of operations shall be performed:
a) One breaking operation of the SCPD shall be performed with all the switching devices
closed prior to the test.
b) One breaking operation of the SCPD shall be performed by closing the contactor or starter
on to the short-circuit.
Table12 - Value of the prospective test current according to the rated operational current

MAKE A FOOTNOTE HERE
NOTE: This test is done if the current Iq is higher than the current "r" .

"r" = The recommended (based on operational current of contactor/starter) prospective test current for table 12

Iq = The rated conditional short-circuit current of the tested device(s). Associated with Icw. (Short Circuit Withstand Current).

9.3.4.2.2 Test the rated conditional short-circuit current Iq

The circuit shall be adjusted to the prospective short-circuit current Iq equal to the rated
conditional short-circuit current.

If the SCPD is a fuse and the test current is within the current-limiting range of the fuse then
if possible, the fuse shall be selected to permit the maximum peak let-through current(Ip) and
the maximum let-through energy(I2t).

The contactor or a starter and the associated SCPD, or the combination or the protected starter shall then be connected to the circuit.

The following sequence of operations shall be performed:
a) One breaking operation of the SCPO shall be performed with all the switching devices closed prior to the test.
b) One breaking operation of the SCPO shall be performed by closing the contactor or starter on to the short-circuit.

If, in the case of a combination starter or a protected starter, the switching device of the
SCPD complies With IEC 60947-2 or IEC 60947-3 and has a short-circuit breaking
capacity or rated conditional short-circuit current less than the rated conditional short circuit current of the combination starter or protected starter the following additional test
shall be made.

;;;;;

c) One breaking operation of the SCPD shall be performed by closing the switching device
(switch or circuit-breaker) on to the short-circuit. This operation may be performed either
on a new sample (starter and SCPD) or on the first sample with the agreement of the
manufacturer.
After this operation only conditions A to G of 9.3.4.2.3 shall be verified.

9.3.4.2.3 Results to be obtained
The contactor, starter, or the combination or protected starter, shall be considered to have
passed the tests at the prospective current "r" and, where applicable, the prospective current
Iq, if the following conditions are met for the claimed type of co-ordination.

Both types of co-ordination (all devices):

A: The fault current has been successfully interrupted by the SCPD or the combination
starter and the fuse or fusible element or solid connection between the enclosure and
supply shall not have melted.

B: The door or cover of the enclosure has not been blown open and it is possible to open the
door or cover. Deformation of the enclosure is considered acceptable provided that the
degree of protection by the enclosure is not less than IP2X.

C: There is no damage to the conductors or terminals and the conductors have not been
separated from the terminals.

D: There is no cracking or breaking of an insulating base to the extent that the integrity of
mounting of alive part is impaired.

Both types of co-ordination (combination starters and protected starters only):

E: The circuit-breaker or the switch is capable of being opened manually by its operating
means.

F: Neither end of the SCPD is completely separated from its mounting means to an exposed
conductive part.

G: If a circuit-breaker with rated ultimate short-circuit breaking capacity less than the rated conditional short-circuit current assigned to the combination or protected starter is employed, the circuit-breaker shall be tested to trip as follows:

a) Circuit-breakers with instantaneous trip relays or releases: At 120 % of the trip current.
b) Circuit-breakers with overload relays or releases: at 250% of the rated current of the
circuit-breaker.

Type"1" co-ordination (all devices):
H: There has been no discharge of parts beyond the enclosure. Damage to the contactor and
the overload relay is acceptable. The starter may be in operative after each operation. The
starter shall therefore be inspected and the contactor and/or the overload relay and the
release of the circuit-breaker shall be reset if necessary and, In the case of fuse
protection, all fuse-links shall be replaced.
pg: 57

Type·1"co-ordination(combination and protected starters only):
The adequacy of insulation in accordance with 8.3.3.4.1.. item .4), of IEC60947-1 is
verified after each operation (at currents "r" and "Iq") by a dielectric test on the complete
unit under test (SCPD plus contactor l starter but before replacement of parts) using a
power frequency withstand voltage of twice the rated operational voltage Ue but not less
than 1 000 V.

The test voltage shall be applied to the incoming supply terminals, with the
switch or the circuit-breaker in the open position, as follows:
_ between each pole and all other poles connected to the frame of the starter;
_ between all live parts of all poles connected together and the frame of the starter;
_ between the terminals of the line side connected together and terminals of the other
side connected together.

For equipment suitable for isolation, the leakage current shall be measured through each
pole, with the contacts in the open position , at a test voltage of 1,1 Ue and shall not
exceed 6mA

Type"2"co-ordination(a/l devices):
J: No damage to the overload relay or other parts has occurred, except that welding of
contactor or starter contacts is permitted, if they are easily separated (e.g. by a
screwdriver) without significant deformation , but no replacement of parts is permitted
during the test, except that, in the case of fuse protection, all fuse-links shall be replaced.
In the case of welded contacts as described above, the functionality of the device shall
be verified by carrying out 10 operating cycles under the conditions of table 8 for the
applicable utilization category.

K: The tripping of the overload relay shall be verified at a multiple of the current setting and
shall conform to the published tripping characteristics, according to 5.7.5, both before and
after the short-circuit test.
l: The adequacy of the insulation in accordance with 8.3.3.4 .1, item 4), of IEC 60947-1 shall
be verified by a dielectric test on the contactor, starter, combination or protected starter
using a power frequency withstand voltage of twice the rated operational voltage Ue
but not less than 1 000 V.

In the case of combination and protected starters, additional tests according to 8.3.3.4.1.
item 3), of IEC 60947-1 shall be made across the main poles of the device with the
contacts of the switch or of the circuit-breaker open and the contacts of the starter closed.

For equipment suitable for isolation, the leakage current shall be measured through each pole, with the contacts In the open position, at la test voltage of 1,1 Ue and shall not exceed 2mA

Fuse-links, if any, are shorted.

============-------------============

8.2.5.2 Co-ordination at the cross over current between starter and associated SCPD Co-ordination at the cross over current between the starter and the SCPD is a special test.

B.4 Co-ordination at the crossover current between the starter and associated SCPD.

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Add as footnote

B.4.1 General and definitions

"r" = The recommended (based on operational current of contactor/starter) prospective test current - for table 12.

Iq = The rated conditional short-circuit current of the tested device(s). Associated with Icw. (Short Circuit Withstand Current).

Ico = Cross over current.

Current corresponding to the cross over point of the mean or published curves representing the time-current characteristics of the overload relay and the SCPD respectively

NOTE The mean curves are the curves corresponding to the average values calculated from the tolerances on the time-current characteristics given by the manufacturer.

Icd = The test current the contactor/starter must break / make under specific test conditions as stipulated in B4.5.11 - Table B2.

Test current greater than lco, tolerances included, designated by the manufacturer and verified by the requirements given in table B.2
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Co-ordination at the crossover current between the starter and the SCPD can be verified either by the direct method with the special test of B.4.2 or, for type "2"co-ordination, by the indirect method as in B.4.5.

B.4.1.2.3: Time-current withstand characteristic capability of contactors/starters locus of the currents a contactor starter can withstand as a function of time.

B.4.2 Condition for the test for the verification of co-ordination at the cross over current by a direct method.
The starter and its associated SCPD shall be mounted and connected as in normal use. All the tests shall be performed starting from the cold state.

B.4.3 Test currents and test circuits

The test circuit shall be according to 8.3.3.5.2 of part1 except that the oscillatory transient voltage need not be

*there is no 8.3.3.5.3 maybe they meant: 9.3.3.5

adjusted. The currents for the tests shall be:
(i) 0,75 lco 0 //-5 % and
(ii) 1.25 lco +5 // 0%

The power factor of the test circuit shall be in accordance with table 7. In the case of small relays having a high resistance, inductors should be mainly used in order to have a value of power factor as low as possible. The recovery voltage shall be 105 times the rated operational voltage. '

pg:78 ISIIEC 60947-4-1: 2000

The SCPD shall be as stated in 8.2 5.1 and of the same rating and characteristics as used in the tests of 9.3.4.2.
If the switching device is a contactor, its coil shall be energized from a separate source at the rated control supply voltage of the contactor coil and connected so that the contactor opens when the overload relay operates.

B.4.4 Test procedure and results to be obtained

B.4.4.1 Test procedure with the starter and the SCPD closed, the test currents stated in 8.4.3 shall be applied by a separate closing device. In each case the device tested shall be at room temperature.

After each test, it is necessary to inspect the SCPD, reset the overload relay and the rei....of the circuit-breaker, if necessary, or to replace all fuses if at least one of them has melted.
B.4.4.2 Results to be obtained after the test at the lower current.

(i) in B.4.3, the SCPD shall not have operated and the overload relay or release shall have operated to open the starter. There shall be no damage to the starter.
After the test at the higher current

(ii) in B.4.3, the SCPD shall have operated before the starter. The starter shall meet the conditions of 9.3.4.2.3 for the type of co-ordination stated by the manufacturer.

B.4.5 Verification of co-ordination at the cross over current by an indirect method

NOTE: For type "1"co-ordination,the indirect method may be different from the method described in annex B end is under consideration. For this reason, the indirect method for the verification of co-ordination at the crossover point is only applicable for type "2" co-ordination.

The indirect method (only for "2" coordination) consists in verifying on a diagram (see figure B.1) that the following conditions for the verification of co-ordination at the crossover current are met:
- the time-current characteristic of the overload relay/release, starting from cold state, supplied by the manufacturer, shall indicate how the tripping time varies with the current up to a value of at least Ico. this curve has to lie below the time-current characteristic of the SCPD up to Ico;
-Icd of the starter, tested as in 8.4.5.1, shall be higher than Ico;
- the time-current with stand characteristic of the contactor, tested as in 8.4.5.2, shall be above the time-current characteristic (starting from cold state) of the overload relay up to Ico

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FOOT NOTE HERE
B.4.5.1 Test for Icd
Sub clause 9.3.4.1applies with the following addition.
- Test procedure :the contactor or starter shall make and break the test current(Icd) for a number of operating cycles given in table 8.2 below. This is made without the SCPD in the circuit.

pg: 79

After this test there shall be no degradation in the operation or components.

8.4.5.2 Time-current characteristic withstand capability of contactors/starters (Overload)

This characteristic is issued by the manufacturer and the values are obtained according to the test procedure specified in 9.3.5 (Overload current test for contactors pg 58 as per 9.3.2 - (at overload values as per 8.2.4.4 -)) but with combinations of overload currents and durations to establish the characteristic at least up to lco. in addition to those stated in 8.2.4.4.

FOOT NOTE THIS
9.3.5 Overload current withstand capability of contactors
For the test. the contactor shall be mounted, wired and operated as specified in 9.3.2.
All poles of the contactors are simultaneously subjected to one test with the overload current
and duration values stated in 8.2.4.4. The test is performed at any convenient voltage and it
starts with the contactor at room temperature.
After the test, the contactor shall be substantially in the same condition as before the test.
This is verified by visual inspection.

NOTE The I2tvalue (Joule integral) calculated from this test cannot be used to estimate the performance of the contactor under short circuit conditions.

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....

This characteristic is valid for overload currents, starting with the contactor at room
temperature. The minimum cooling duration required by the contactor between two such
overload tests should be stated by the manufacturer.

This characteristic is valid for overload currents, starting with the contactor at room temperature. The minimum cooling duration required by the contactor between two such overload tests should be stated by the manufacturer.

The final step is above graph...

Superimpose the contactor and the SCPD switch trip graph and where the two intersect we call it the changeover current (Ico).

Compare the Icd and the contactor only tested current (Icd) with Ico and it must be larger then Ico.

But Icd is already proven not to be damaging to the starter so we have passed all tests.

What a process...took me days to get here!

CB must accommodate start current.

CB must be set at motor FLC and must trip - inversely proportional from 120/125%xFLC.

Please read with these limitations:

Continuous duty motors only.

Single point motor protection only.

Overload protection only.

Separate type motor protection only

600Vac and lower category only.

Motors > 1hp and smaller then 1500hp.

Non shunted applications (no stopping during starting) so in other words we are only discussing the normal applications.

OVERLOAD PROTECTION:

Article 430.32(a) allow the following:

*FLC = Full Load Current as on motor name plate

Motors with a marked service factor 1.15 or greater: Max 125%FLC
Motors with a marked temperature rise 40°C or less: Max 125%FLC
All other motors: Max 115%FLC

Then Article article 430.32(c) comes and changes the rules with:

If Article 430.32(a) does not succeed in starting or running then one is allowed the following:

Motors with marked service factor 1.15 or greater 140%FLC
Motors with a marked temperature rise 40°C or less 140%FLC
All other motors 130%FLC

+ and the following informational note: Consider different starter classes to allow the adequate starting time rather then upgrading the overload.

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Motor overload class protection – do not forget there are different classes of motor according to Nema A,D,C,D,E etc.

Rated frequency, when necessary (for example in the case of a current transformer operated overload relay) ;

time-current characteristics (or range of characteristics), when necessary;

trip class according to classification in table 2, or the value of the maximum tripping time, in seconds, under the conditions specified in 8.2.1.5.1, table 3, column 0, when this 'time exceeds 30 s;

8.2.1.5 Limits of operation of current operated relays and releases

8.2.1.5.1 Limits of operation of tlme-delay overload relays when all poles are energized

The relays shall comply with the requirements of table3 when tested as follows:
*With the overload relay or starter in its enclosure, if normally fitted,

TABLE 3

	A	B	C	D
Thermal type not temp compensated Ref temp: -5, +20,+40DegC It makes no sense that a NOT temp compensated O/L be tested across different temp ranges for the same conditions - the temp comp one should comply to this.	1 (This makes no sense - and is not in manufacturers data)	1.2	1.5	7.2
Thermal type temp comp -5	1.05	1.3	1.5	-
Thermal type temp comp +20	1.05	1.2	1.5	7.2
Thermal type temp comp -40	1 (This makes no sense - and is not in manufacturers data)	1.2	1.5	-
Electronic type Ref temp: -5, +20,+40DegC	1.05	1.2	1.5	7.2
	A times the current setting, tripping shall not occur in less than 2h starting from the cold state, at the value of reference ambient air temperature stated in table3. However, when the overload relay terminals have reached thermal equilibrium at the test current in less than 2h,the test duration can be the time needed to reach such thermal equilibrium;	When the current is subsequently raised to B times the current setting, tripping shall occur in less than 2h;	Class10A overload - in less than 2min starting from thermal equilibrium, at the current setting, in accordance with8.2.3 of IEC 60034-1; Class 10, 20 and 30 - tripping shall occur in less than 4, 8 or 12 min respectively, starting from thermal equilibrium, at the current setting;	Tripping shall occur within the limits given in table 2 for the appropriate trip class, starting from the cold state

NOTE 1 Depending on the nature of the relay, the tripping conditions are given in 8.2.1.5.

NOTE 2 In the case of a rheostatic rotor starter. the overload relay Is commonly Inserted In the stator circuit.
As a result, it cannot efficiently protect the rotor circuit end more particularly the resmors (generally mor a easily
damageablethan the rotoritself or theswitchingdevlc..in caseof afaulty start); protectionofthe rotor circuit
should ~the SUbject of a specificagreement~tw..nmanufacturerand usar (see, inter alia, 8.2.1.1.3).

NOTE 3 In the case of a two-step auto-transformer starter, the shirting auto-transformer Is normallydesigned
for use during the startingperiodonly: asaresult, it cannot ~effICientlyprotectedbythe overloedrelay in the
event of faulty starting. Protection of the auto-transformer should be the subject of specifIC agreement between
manufacturer and user (see 8.2.1.1.4) .

NOTE 4 The lower limiting values of T D are selected to allow for differing heater characteristics and manufacturing tolerances.

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In the case of overload relays having a current setting range, the limits of operation shall
apply when the relay is carrying the current associated with the maximum setting and also
when the relay is carrying the current associated with the minimum setting.

For non-compensated overload relays, the current multiple /ambient temperature characteristic
shall not be greater than 1,2%/K.

NOTE 1,2'l(,/Kis the derating characteristic of PVC·insulated conductors.

An overload relay is regarded as compensated it it complies with the relevant requirements of
table 3 at +20 ·C and is within the limits shown in figure 7 at other temperatures.

Table 3 -Limits of operation of tlme-delay overload relays when energized on" Ipol••

OLD TABLE:

a The manufacturer shall add the letter E to trip classes to indicate compliance will he band E.
NOTE 1: Depending on the nature of the relay, the tripping conditions are given in 8.2.1.5.
NOTE 2: In the case of a rheostat rotor starter, the overload relay is commonly inserted in the stator circuit.

As a result, one cannot efficiently protect the rotor circuit and more particularly the resistors (generally more easily
damageable than the rotor ,itself or the switching devices in case of a faulty start);

protection of the rotor circuit should be the subject of a specific agreement between manufacturer and user (see, inter alia, 8.2.1.1.3).
NOTE 3 In the case of a two-step auto-transformer starter, the starting auto-transformer is normally designed for
use during the starting period only, as a result, it cannot be efficiently protected by the overload relay in the event
of faulty starting Protection of the auto-transformer should be the subject of specific agreement between
manufactureranduser(see 82114).
NOTE 4 The lower limning values of Tp are selected to allow for differing heater characteristics and
manufacturing tolerances

8.2.1 .5.1.1 General tripping requirements of overload relays

NOTE 1 The thermal protection of motors in the presence of harmonics in the supply voltage is under
consideration.
Replace the existing item c) by the following:
c) for class 2, 3, 5 and 10A overload relays energized at C times the current setting, tripping
shall occur in less than 2 min starting from thermal equilibrium, at the current setting, in
accordance with 9.3.3 of IEC 60034-1:

NOTE 2 Sub clause 93.3 of lEC 60034-1 states: 'Polyphase motors having rated outputs not exceeding
315 kW and rated voltages not exceeding 1 kV shall be capable of withstanding a current equal to 1,5 times
the rated current for not less than 2 min.'.

About reticulation protection to a motor

Circuit breakers and Combination motor Controllers (with above limitations)

430.52 Rating or Setting for Individual Motor Circuit.
(A) General. The motor branch-circuit short-circuit and ground-fault protective device shall comply with

430.52(B) -(B) All Motors.The motor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor.

and either

430.52(C) - (C) Rating or Setting.

430.52(D), - Torque motors

as applicable.

It starts with the basics from Table 430.52

Instantaneous current max 800%FLC

Long time delay/inverse curve/overload max 250%FLC

If setting on device is not adequate - An exception gives licence to increase this value to the next "standard current rating" available.

If the motor does not start here then another exception - very confusing one at that- SUDDENLY YOU CAN INCREASE THE OVERLOAD VALUE TO:

for less then 100Amps then you can increase O/L to max. 400%FLC

for higher then 100Amp you can increase to max. 300%FLC

Then they mix it all up with an even more confusing:

Instantaneous Trip Circuit Breaker must be adjustable and if in a "combination motor controller" the setting is adjusted to no more than the value specified in Table 430.52.

One would think it ends there but no - this will blow the mind even more, it seems they threw caution to the wind at this point:

Exception No. 1: If motor does not start then you can set inst. to max 1300%FLC and even 1700%FLC for B design - energy efficient motors. Wow, wow, wow! With a note that it must be "demonstrated by engineering evaluation"

430.52(c) 6 exception 1: All is reiterated here:

(6) Self-Protected Combination Controller. A listed self protected combination controller shall be permitted in lieu of the devices specified in Table 430.52. Adjustable instantaneous-trip settings shall not exceed 1300 percent of full-load motor current for other than Design B energy-efficient motors and not more than 1700 percent of full-load motor current for Design B energy-efficient
motors.

AND THEN THE FINAL CURVE BALL:

430.52(c)3 Exception No. 2: Where the motor full-load current is 8 amperes or less, the setting of the instantaneous-trip circuit breaker with a continuous current rating of 15 amperes or less in a listed combination motor controller that provides coordinated motor branch-circuit overload and short-circuit and ground-fault protection shall be permitted to be increased to the value marked on the controller.

I don't know what is happening in this decision making processes for the code but this is strange,

9.3.3.2.2 Relays and releases

a) Operation of under-voltage relays and releases

Under-voltage relays or releases shall be tested for compliance with the requirements of 8.2.1.3. Each limit shall be verified three times.

For the drop-out test, the voltage shall be reduced from the rated value to zero at an uniform rate in approximately 1 min.

b) Shunt-coil operated releases

Shunt-coil operated releases shall be tested for compliance with the requirements of 8.2.1.4.

Operation shall be verified at 70 % and 110 % of rated voltage under all operating conditions of the starter.

c) Thermal and time-delay magnetic overload relays

Overload relays and starters shall be connected using conductors in accordance with tables 9, 10 and 11 of part 1 for test currents corresponding to:

- 100 % of the current setting of the overload relay for overload relays of trip class 10A;

- 125 % of the current setting of the overload relay for overload relays of trip classes 10,

20 and 30 and for overload relays for which a maximum tripping time greater than 30 s

is specified (see 5.7.3).

Thermal and time-delay magnetic overload relays with all poles energized shall be tested

as stated in 8.2.1.5.1.

Moreover, the characteristics defined in 8.2.1.5.1 shall be verified by tests at -5 ·C,

+20 ·C, +40 ·C and may be verified at minimum and maximum temperatures given by the

manufacturer if larger. However, for relays or releases declared compensated for ambient

temperature, in case of temperature range declared by the manufacturer larger than those

given in figure 7, the characteristics at -5 ·C and/or +40 ·C need not be verified if, when

tested at the declared minimum and maximum temperatures, the corresponding tripping

current values are in compliance with the limits specified for -5 ·C and/or +40 ·C in that

figure.

Three-pole thermal overload relays energized on two poles only shall be tested as stated

in 8.2.1.5.2 on all combinations of poles and at the maximum and minimum current

settings for relays with adjustable settings.

d) Instantaneous magnetic overload relays

Each relay shall be tested separately. The current through the relay shall be increased

at a rate suitable for an accurate reading to be made. The values shall be as stated

in 8.2.1.5.3.

e) Under-current relays in automatic change-over

The limits of operation shall be verified in accordance with 8.2.1.5.4.

9.3.3.3 Temperature rise

9.3.3.3.1 Ambient air temperature

Subclause 8.3.3.3.1 of part 1 applies.

9.3.3.3.2 Measurement of the temperature of parts

Subclause 8.3.3.3.2 of part 1 applies.

CB must protect cable at cable current rating.

CB must be rated at load current at 80% Ir (unless 100% rated)

the cable must be sized 125%FLC

.....

Motor overload class protection – do not forget there are different classes of motor according to Nema A,D,C,D,E etc.

And Nema also has a definition for different classes of overloads.

Overload relay classes:

This is not an NEC thing though it is mentioned there. I found this in the NEMA standards:

3. Classifications: Inverse Time Overload relays pg 4-3

This is what it says: At 600%FLC - Balanced in all phases condition:

Class 10	Must trip in max 10sec
Class 20	Must trip in max 20sec
Class 30	Must trip in max 30sec

What is mentioned is they have different categories too:

Category
A	Non volatile memory
B	Volatile memory
C	No operating memory

There is even an "Instantaneous Overload Relay" which off-course has no time delay but rather a disabling input to cope with starting normal high current situations.

Overload classes

For those of us who like graphs and charts…there is deeper discussion on overload trips here…for those who does not know:

What does the standards say about motor overload protection?

Note 1:

Ahh, and do not forget there are different classes of overloads as well…the most common in industry is class 10 – these are the ones you will normally get at the electrical wholesaler.

Note 2:

Did you know a circuit breaker has similar tripping characteristics (Proportional Inverse Trip curve.

Note 3:

My question to the Americans is: You guys use fuses to protect even three phase installations…I know it is in order to qualify the kA rating for downstream equipment but is this not more trouble for what it is worth? Circuit breakers do just fine and single phasing is nearly an impossibility.

machines, IEC60034-30, four different

efficiency classes have been defined. The

classes are called IE1, IE2, IE3 and IE4,

where motors belonging to IE4 are the

...

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Air intake/outlet positions; Instinctively I always positioned the outlet on top corner and intake in diagonally opposite bottom corner – NOW I see why!

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Condensation for electronics left unpowered/off

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Softstarers on one line supply

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Is it all the same – plastic or metal enclosure – Is this true! Softstarter lovato

Cable selection for motor loads:

	NEC 430
	430.24Several Motors or a Motor(s) and Other Load(s). Conductors supplying several motors, or a motor(s) and other load(s), shall have an ampacity not less than the sum of each of the following: (1) 125 percent of the full-load current rating of the highest rated motor, as determined by 430.6(A) (2) Sum of the full-load current ratings of all the other motors in the group, as determined by 430.6(A) (3) 100 percent of the noncontinuous non-motor load (4) 125 percent of the continuous non-motor load.

jbjg

NEC circuit breaker motor protection notes:

VII. Service Equipment — Overcurrent Protection

230.90 Where Required, Each ungrounded service conductor shall have overload protection.

(A) Ungrounded Conductor. Such protection shall be provided by an over current device in series with each ungrounded
service conductor that has a rating or setting not higher than the allowable ampacity of the conductor.

A set of fuses shall be considered all the fuses required to protect all the ungrounded conductors of a circuit.

Single-pole circuit breakers, grouped in accordance with 230.71(B), shall be considered as one protective device.
230.71 Use of up to 6 single phase cb or isolators with handles locked together can be used on a multiphase circuit

Exception No. 1: For motor-starting currents, ratings that comply with 430.52, 430.62, and 430.63 shall be permitted.

Exception No. 2: Fuses and circuit breakers with a rating or setting that complies with 240.4(B) or (C) and 240.6
shall be permitted.

Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit
breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not
exceed the ampacity of the service conductors.

Exception No. 4: Overload protection for fire pump supply conductors shall comply with 695.4(B)(2)(a).

Exception No. 5: Overload protection for 120/240-volt,3-wire, single-phase dwelling services shall be permitted in
accordance with the requirements of 310.15(B)(6).

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230.91 cb Location.

The service overcurrent device shall be an integral part of the service disconnecting means or shall be located immediately adjacent thereto.

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430.32 Continuous-Duty Motors.

* Any motor application shall be considered to be for continuous duty unless the nature of the apparatus it drives is such that the motor cannot operate continuously with load under any condition of use.

(A) More Than 1 Horsepower.

Each motor used in a continuous duty application and rated more than 1 hp shall be protected against overload by one of the means in 430.32(A)(1) through (A)(4).

(1) Separate Overload Device.

A separate overload device that is responsive to motor current.

This device shall be selected to trip or shall be rated at no more than the following percent of the motor nameplate full-load current rating:

Motors with a marked service factor 1.15 or greater: 125%
Motors with a marked temperature rise 40°C or less: 125%
All other motors: 115%

(2) Thermal Protector.

A thermal protector integral with the motor, approved for use with the motor it protects on the basis that it will prevent dangerous overheating of the motor due to overload and failure to start.

The ultimate trip current of a thermally protected motor shall not exceed the following percentage of motor full-load current given in Table 430.248, Table 430.249, and Table 430.250:

Motor full-load current 9 amperes or less: 170%

Motor full-load current from 9.1 to, and including, 20 amperes: 156%

Motor full-load current greater than 20 amperes: 140%

If the motor current-interrupting device is separate from the motor and its control circuit is operated by a protective device integral with the motor, it shall be arranged so that the opening of the control circuit will result in interruption of current to the motor.

(3) Integral with Motor. A protective device integral with a motor that will protect the motor against damage due to

failure to start shall be permitted if the motor is part of an approved assembly that does not normally subject the motor to overloads.

(4) Larger Than 1500 Horsepower. For motors larger than 1500 hp, a protective device having embedded temperature

detectors that cause current to the motor to be interrupted when the motor attains a temperature rise greater than marked

on the nameplate in an ambient temperature of 40°C.

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430.32(B) One Horsepower or Less, Automatically Started.

Any motor of 1 hp or less that is started automatically shall be protected against overload by one of the following means.

(1) Separate Overload Device. By a separate overload device following the requirements of 430.32(A)(1).

For a multispeed motor, each winding connection shall be considered separately. Modification of this value shall be

permitted as provided in 430.32(C).

(2) Thermal Protector. A thermal protector integral with the motor, approved for use with the motor that it protects

on the basis that it will prevent dangerous overheating of the motor due to overload and failure to start. Where the

motor current-interrupting device is separate from the motor and its control circuit is operated by a protective device

integral with the motor, it shall be arranged so that the opening of the control circuit results in interruption of current to the motor.

(3) Integral with Motor. A protective device integral with a motor that protects the motor against damage due to failure to start shall be permitted (1) if the motor is part of an approved assembly that does not subject the motor to overloads, or (2) if the assembly is also equipped with other safety controls (such as the safety combustion controls on a domestic oil burner) that protect the motor against damage due to failure to start. Where the assembly has safety controls that protect the motor, it shall be so indicated on the nameplate of the assembly where it will be visible after installation.

(4) Impedance-Protected. If the impedance of the motor windings is sufficient to prevent overheating due to failure to start, the motor shall be permitted to be protected as specified in 430.32(D)(2)(a) for manually started motors if the motor is part of an approved assembly in which the motor will limit itself so that it will not be dangerously overheated.

Informational Note: Many ac motors of less than 1⁄20 hp, such as clock motors, series motors, and so forth, and also some larger motors such as torque motors, come within this classification. It does not include split-phase motors having automatic switches that disconnect the starting windings

430.32(C) Selection of Overload Device.

Where the sensing element or setting or sizing of the overload device selected in accordance with 430.32(A)(1) and 430.32(B)(1) is not sufficient to start the motor or to carry the load, higher size sensing elements or incremental settings or sizing shall be permitted to be used, provided the trip current of the overload device does not exceed the following percentage of motor nameplate full-load current rating:

Motors with marked service factor 1.15 or greater 140%

Motors with a marked temperature rise 40°C or less 140%

All other motors 130%

If not shunted during the starting period of the motor as provided in 430.35, the overload device shall have sufficient time delay to permit the motor to start and accelerate its load.

Informational Note: A Class 20 or Class 30 overload relay will provide a longer motor acceleration time than a Class 10 or Class 20, respectively. Use of a higher class overload relay may preclude the need for selection of a higher trip

current.

(D) One Horsepower or Less, Nonautomatically Started.

(1) Permanently Installed. Overload protection shall be in accordance with 430.32(B).

(2) Not Permanently Installed.

(a) Within Sight from Controller. Overload protection shall be permitted to be furnished by the branch circuit short-circuit and ground-fault protective device;

such device, however, shall not be larger than that specified in Part IV of Article 430.

Exception: Any such motor shall be permitted on a nominal 120-volt branch circuit protected at not over 20 amperes.

(b) Not Within Sight from Controller. Overload protection shall be in accordance with 430.32(B).

(E) Wound-Rotor Secondaries.

The secondary circuits of wound-rotor ac motors, including conductors, controllers, resistors, and so forth, shall be permitted to be protected against overload by the motor-overload device.

430.33 Intermittent and Similar Duty.

A motor used for a condition of service that is inherently short-time, intermittent, periodic, or varying duty, as illustrated by Table 430.22(E), shall be permitted to be protected against overload by the branch-circuit short-circuit and ground-fault protective device, provided the protective device rating or setting does not exceed that specified in Table 430.52.

Any motor application shall be considered to be for continuous duty unless the nature of the apparatus it drives is such that the motor cannot operate continuously with load under any condition of use.

430.35 Shunting During Starting Period.

(A) Non automatically Started. For a non automatically started motor, the overload protection shall be permitted

to be shunted or cut out of the circuit during the starting period of the motor if the device by which the overload

protection is shunted or cut out cannot be left in the starting position and if fuses or inverse time circuit

breakers rated or set at not over 400 percent of the full load current of the motor are located in the circuit so as

to be operative during the starting period of the motor.

(B) Automatically Started. The motor overload protection shall not be shunted or cut out during the starting period if the

motor is automatically started.

Exception: The motor overload protection shall be permitted to be shunted or cut out during the starting period on

an automatically started motor where the following apply:

(a) The motor starting period exceeds the time delay of available motor overload protective devices, and

(b) Listed means are provided to perform the following:

(1) Sense motor rotation and automatically prevent the shunting or cutout in the event that the motor fails to

start, and

(2) Limit the time of overload protection shunting or cutout to less than the locked rotor time rating of the protected

motor, and

(3) Provide for shutdown and manual restart if motor running condition is not reached

430.36 Fuses — In Which Conductor.

Where fuses are used for motor overload protection, a fuse shall be inserted in each ungrounded conductor and also in the grounded conductor if the supply system is 3-wire, 3-phase ac with

one conductor grounded.

430.37 Devices Other Than Fuses — In Which Conductor.

Where devices other than fuses are used for motor overload protection, Table 430.37 shall govern the minimum allowable number and location of overload units such as trip coils or relays.

430.38 Number of Conductors Opened by Overload Device.

Motor overload devices, other than fuses or thermal protectors, shall simultaneously open a sufficient number of ungrounded conductors to interrupt current flow to the motor

430.39 Motor Controller as Overload Protection.

A motor controller shall also be permitted to serve as an overload device if the number of overload units complies with Table 430.37 and if these units are operative in both the starting and running position in the case of a dc motor, and in the running position in the case of an ac motor.

430.40 Overload Relays.

Overload relays and other devices for motor overload protection that are not capable of opening short circuits or ground faults shall be protected by fuses or circuit breakers with ratings or settings in accordance with 430.52 or by a motor short-circuit protector in accordance with 430.52.

Exception: Where approved for group installation and marked to indicate the maximum size of fuse or inverse time

circuit breaker by which they must be protected, the overload devices shall be protected in accordance with this marking.

430.42 Motors on General-Purpose Branch Circuits.

Overload protection for motors used on general-purpose branch circuits as permitted in Article 210 shall be provided as specified in 430.42(A), (B), (C), or (D).

(A) Not over 1 Horsepower. One or more motors without individual overload protection shall be permitted to be connected to a general-purpose branch circuit only where the installation complies with the limiting conditions specified in 430.32(B) and 430.32(D) and 430.53(A)(1) and (A)(2).

(B) Over 1 Horsepower. Motors of ratings larger than specified in 430.53(A) shall be permitted to be connected to general-purpose branch circuits only where each motor is protected by overload protection selected to protect the motor as specified in 430.32. Both the controller and the motor overload device shall be approved for group installation with the short-circuit and ground-fault protective device selected in accordance with 430.53

(C) Cord-and-Plug-Connected. Where a motor is connected to a branch circuit by means of an attachment plug and a receptacle or a cord connector, and individual overload protection is omitted as provided in 430.42(A), the rating of the attachment plug and receptacle or cord connector shall not exceed 15 amperes at 125 volts or 250 volts. Where individual overload protection is required as provided in 430.42(B) for a motor or motor-operated appliance that is attached to the branch circuit through an attachment plug and a receptacle or a cord connector, the overload device shall be an integral part of the motor or of the appliance. The rating of the attachment plug and receptacle or the cord connector shall determine the rating of the circuit to which the motor may be connected, as provided in 210.21(B).

(D) Time Delay. The branch-circuit short-circuit and ground fault protective device protecting a circuit to which a motor or motor-operated appliance is connected shall have sufficient time delay to permit the motor to start and accelerate its load

430.43 Automatic Restarting.

A motor overload device that can restart a motor automatically after overload tripping shall not be installed unless approved for use with the motor it protects. A motor overload device that can restart a motor automatically after overload tripping shall not be installed if automatic restarting of the motor can result in injury to persons.

430.44 Orderly Shutdown.

If immediate automatic shutdown of a motor by a motor overload protective device(s) would introduce additional or increased hazard(s)

to a person(s) and continued motor operation is necessary for safe shutdown of equipment or process, a motor

overload sensing device(s) complying with the provisions of Part III of this article shall be permitted to be

connected to a supervised alarm instead of causing immediate interruption of the motor circuit, so that corrective action or an orderly shutdown can be initiate

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IV. Motor Branch-Circuit Short-Circuit and Ground-Fault Protection

430.51 General.

Part IV specifies devices intended to protect the motor branch-circuit conductors, the motor control apparatus, and the motors against overcurrent due to short circuits or ground faults. These rules add to or amend the provisions of Article 240.

The devices specified in Part IV do not include the types of devices required by 210.8, 230.95, and 590.6.

The provisions of Part IV shall not apply to motor circuits rated over 600 volts, nominal.

Informational Note No. 1: For over 600 volts, nominal, see Part XI.

Informational Note No. 2: See Informative Annex D, Example D8.

430.52 Rating or Setting for Individual Motor Circuit.

(A) General. The motor branch-circuit short-circuit and ground-fault protective device shall comply with 430.52(B) and either 430.52(C) or (D), as applicable.

(B) All Motors. The motor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor

(C) Rating or Setting.

(1) In Accordance with Table 430.52. A protective device that has a rating or setting not exceeding the value calculated according to the values given in Table 430.52 shall be used.

Exception No. 1:Where the values for branch-circuit shortcircuit and ground-fault protective devices determined by Table 430.52 do not correspond to the standard sizes or ratings of fuses, nonadjustable circuit breakers, thermal protective devices, or possible settings of adjustable circuit breakers, a higher size, rating, or possible setting that does not exceed the next higher standard ampere rating shall be permitted.

Exception No. 2: Where the rating specified in Table 430.52, or the rating modified by Exception No. 1, is not suffıcient for the starting current of the motor:

(a) The rating of a nontime-delay fuse not exceeding 600 amperes or a time-delay Class CC fuse shall be permitted to be increased but shall in no case exceed 400 percent of the

full-load current.

(b) The rating of a time-delay (dual-element) fuse shall be permitted to be increased but shall in no case exceed 225 percent of the full-load current.

(c) The rating of an inverse time circuit breaker shall be permitted to be increased but shall in no case exceed 400 percent for full-load currents of 100 amperes or less or 300 percent for full-load currents greater than 100 amperes.

(d) The rating of a fuse of 601–6000 ampere classification shall be permitted to be increased but shall in no case exceed 300 percent of the full-load current.

Informational Note: See Informative Annex D, Example D8, and Figure 430.1.

(2) Overload Relay Table. Where maximum branch-circuit short-circuit and ground-fault protective device ratings are shown in the manufacturer’s overload relay table for use with a motor controller or are otherwise marked on the equipment, they shall not be exceeded even if higher values are allowed as shown above.

(3) Instantaneous Trip Circuit Breaker. An instantaneous trip circuit breaker shall be used only if adjustable and if part of a listed combination motor controller having coordinated motor overload and short-circuit and ground-fault protection in each conductor, and the setting is adjusted to no more than the value specified in Table 430.52.

Informational Note: For the purpose of this article, instantaneous trip circuit breakers may include a damping means to accommodate a transient motor inrush current without nuisance tripping of the circuit breaker.

Exception No. 1: Where the setting specified in Table 430.52 is not suffıcient for the starting current of the motor, the setting of an instantaneous trip circuit breaker shall be permitted to be increased but shall in no case exceed 1300 percent of the motor full-load current for other than Design B energy effıcient motors and no more than 1700 percent of full-load motor current for Design B energy-effıcient motors. Trip settings above 800 percent for other than Design B energyeffıcient motors and above 1100 percent for Design B energy effıcient motors shall be permitted where the need has been demonstrated by engineering evaluation. In such cases, it shall not be necessary to first apply an instantaneous-trip circuit breaker at 800 percent or 1100 percent.

Informational Note: For additional information on the requirements for a motor to be classified “energy efficient,” see NEMA Standards Publication No. MG1-1993, Revision,Motors and Generators,Part 12.59.

Exception No. 2: Where the motor full-load current is 8 amperes or less, the setting of the instantaneous-trip circuit breaker with a continuous current rating of 15 amperes or less in a listed combination motor controller that provides coordinated motor branch-circuit overload and short-circuit and ground-fault protection shall be permitted to be increased to the value marked on the controller

(4) Multispeed Motor. For a multispeed motor, a single short-circuit and ground-fault protective device shall be permitted for two or more windings of the motor, provided the rating of the protective device does not exceed the above applicable percentage of the nameplate rating of the smallest winding protected.

Exception: For a multispeed motor, a single short-circuit and ground-fault protective device shall be permitted to be used and sized according to the full-load current of the highest current winding, where all of the following conditions are met:

(a) Each winding is equipped with individual overload protection sized according to its full-load current.

(b) The branch-circuit conductors supplying each winding are sized according to the full-load current of the

highest full-load current winding.

(c) The controller for each winding has a horsepower rating not less than that required for the winding having the highest horsepower rating.

(5) Power Electronic Devices. Suitable fuses shall be permitted in lieu of devices listed in Table 430.52 for power electronic devices in a solid-state motor controller system, provided that the marking for replacement fuses is provided adjacent to the fuses.

(6) Self-Protected Combination Controller. A listed selfprotected combination controller shall be permitted in lieu of the devices specified in Table 430.52. Adjustable instantaneous-trip settings shall not exceed 1300 percent of full-load motor current for other than Design B energy-efficient motors and not more than 1700 percent of full-load motor current for Design B energy-efficient motors.

Informational Note: Proper application of self-protected combination controllers on 3-phase systems, other than solidly grounded wye, particularly on corner grounded delta

systems, considers the self-protected combination controllers’ individual pole-interrupting capability.

(7) Motor Short-Circuit Protector. A motor short-circuit protector shall be permitted in lieu of devices listed in Table 430.52 if the motor short-circuit protector is part of a listed combination motor controller having coordinated motor overload protection and short-circuit and ground-fault protection in each conductor and it will open the circuit at currents exceeding 1300 percent of motor full-load current for other than Design B energy-efficient motors and 1700 percent of motor full-load motor current for Design B energy-efficient motors.

Informational Note: A motor short-circuit protector, as used in this section, is a fused device and is not an instantaneous trip circuit breaker.

(D) Torque Motors. Torque motor branch circuits shall be protected at the motor nameplate current rating in accordance with 240.4(B).

430.53 Several Motors or Loads on One Branch Circuit.

Two or more motors or one or more motors and other loads shall be permitted to be connected to the same branch circuit under conditions specified in 430.53(D) and in 430.53(A), (B), or (C). The branch-circuit protective device shall be fuses or inverse time circuit breakers.m

(A) Not Over 1 Horsepower.

Several motors, each not exceeding 1 hp in rating, shall be permitted on a nominal 120-volt branch circuit protected at not over 20 amperes or a

branch circuit of 600 volts, nominal, or less, protected at not over 15 amperes, if all of the following conditions are met:

(1) The full-load rating of each motor does not exceed 6 amperes.

(2) The rating of the branch-circuit short-circuit and groundfault protective device marked on any of the controllers is

not exceeded.

(3) Individual overload protection conforms to 430.32

(B) If Smallest Rated Motor Protected.

If the branchcircuit short-circuit and ground-fault protective device is selected not to exceed that allowed by 430.52 for the smallest rated motor, two or more motors or one or more motors

and other load(s), with each motor having individual overload protection, shall be permitted to be connected to a

branch circuit where it can be determined that the branchcircuit short-circuit and ground-fault protective device will

not open under the most severe normal conditions of service that might be encountered.

(C) Other Group Installations. Two or more motors of any rating or one or more motors and other load(s), with each

motor having individual overload protection, shall be permitted to be connected to one branch circuit where the motor

controller(s) and overload device(s) are

(1) installed as a listed factory assembly and the motor branch-circuit short-circuit and ground-fault protective device either is provided as part of the assembly or is specified by a marking on the assembly, or

(2) the motor branch-circuit short-circuit and ground-fault protective device, the motor controller(s), and overload device(s)

are field-installed as separate assemblies listed for such use and provided with manufacturers’ instructions for use with

each other, and

(3) all of the following conditions are complied with:

(1) Each motor overload device is either (a) listed for group installation with a specified maximum rating of fuse, inverse time circuit breaker, or both, or (b) selected such

that the ampere rating of the motor-branch short-circuit and ground-fault protective device does not exceed that

permitted by 430.52 for that individual motor overload device and corresponding motor load.

(2) Each motor controller is either

(a) listed for group installation with a specified maximum rating of fuse, circuit

breaker, or both, or

(b) selected such that the ampere rating of the motor-branch short-circuit and ground-fault protective device does not exceed that permitted by 430.52 for that individual controller and corresponding motor load.

(3) Each circuit breaker is listed and is of the inverse time type.

(4) The branch circuit shall be protected by fuses or inverse time circuit breakers having a rating not exceeding that specified in 430.52 for the highest rated motor connected

to the branch circuit plus an amount equal to the sum of the full-load current ratings of all other motors and the

ratings of other loads connected to the circuit. Where this calculation results in a rating less than the ampacity of the

supply conductors, it shall be permitted to increase the maximum rating of the fuses or circuit breaker to a value

not exceeding that permitted by 240.4(B).

(5) The branch-circuit fuses or inverse time circuit breakers are not larger than allowed by 430.40 for the overload

relay protecting the smallest rated motor of the group.

(6) Over current protection for loads other than motor loads shall be in accordance with Parts I through VII of Article 240.

Informational Note: See 110.10 for circuit impedance and other characteristics.

(D) Single Motor Taps. For group installations described above, the conductors of any tap supplying a single motor

shall not be required to have an individual branch-circuit short-circuit and ground-fault protective device, provided

they comply with one of the following:

(1) No conductor to the motor shall have an ampacity less than that of the branch-circuit conductors.

(2) No conductor to the motor shall have an ampacity less than one-third that of the branch-circuit conductors, with a minimum in accordance with 430.22, the conductors to the motor overload device being not more

than 7.5 m (25 ft) long and being protected from physical damage by being enclosed in an approved raceway or by use of other approved means.

(3) Conductors from the branch-circuit short-circuit and ground-fault protective device to a listed manual motor

controller additionally marked “Suitable for Tap Conductor Protection in Group Installations,” or to a branchcircuit protective device, shall be permitted to have an

ampacity not less than one-tenth the rating or setting of the branch-circuit short-circuit and ground-fault protective device. The conductors from the controller to the motor shall have an ampacity in accordance with 430.22. The

conductors from the branch-circuit short-circuit and ground-fault protective device to the controller shall

(1) be suitably protected from physical damage and enclosed either by an enclosed controller or by a raceway and be

not more than 3 m (10 ft) long or

(2) have an ampacity not less than that of the branch-circuit conductors.

430.54 Multimotor and Combination-Load Equipment.

The rating of the branch-circuit short-circuit and ground-fault protective device for multimotor and combination-load equipment shall not exceed the rating marked on the equipment in

accordance with 430.7(D).

430.55 Combined Overcurrent Protection.

Motor branch circuit short-circuit and ground-fault protection and motor overload protection shall be permitted to be combined in a

single protective device where the rating or setting of the device provides the overload protection specified in 430.32.

430.56 Branch-Circuit Protective Devices — In Which Conductor.

Branch-circuit protective devices shall comply with the provisions of 240.15.

430.57 Size of Fuseholder.

Where fuses are used for motor branch-circuit short-circuit and ground-fault protection, the fuseholders shall not be of a smaller size than required to accommodate the fuses specified by Table 430.52.

Exception: Where fuses having time delay appropriate for the starting characteristics of the motor are used, it shall be permitted to use fuseholders sized to fit the fuses that are used.

430.58 Rating of Circuit Breaker.

A circuit breaker for motor branch-circuit short-circuit and ground-fault protection shall have a current rating in accordance with 430.52

and 430.110.

V. Motor Feeder Short-Circuit and Ground-Fault Protection

430.61 General.

Part V specifies protective devices intended to protect feeder conductors supplying motors against overcurrents due to short circuits or grounds.

Informational Note: See Informative Annex D, Example D8.

430.62 Rating or Setting — Motor Load.

(A) Specific Load. A feeder supplying a specific fixed motor load(s) and consisting of conductor sizes based on 430.24 shall be provided with a protective device having a

rating or setting not greater than the largest rating or setting of the branch-circuit short-circuit and ground-fault protective device for any motor supplied by the feeder [based on

the maximum permitted value for the specific type of a protective device in accordance with 430.52, or 440.22(A) for hermetic refrigerant motor-compressors], plus the sum

of the full-load currents of the other motors of the group.

Where the same rating or setting of the branch-circuit short-circuit and ground-fault protective device is used on

two or more of the branch circuits supplied by the feeder, one of the protective devices shall be considered the largest

for the above calculations.

Exception No. 1: Where one or more instantaneous trip circuit breakers or motor short-circuit protectors are used for motor branch-circuit short-circuit and ground-fault protection as permitted in 430.52(C), the procedure provided above for determining the maximum rating of the feeder protective device shall apply with the following provision: For the purpose of the calculation, each instantaneous trip circuit breaker or motor short-circuit protector shall be assumed to have a rating not exceeding the maximum percentage of motor full-load current permitted by Table 430.52 for the type of feeder protective device employed.

Exception No. 2: Where the feeder overcurrent protective device also provides overcurrent protection for a motor control center, the provisions of 430.94 shall apply.

Informational Note: See Informative Annex D, Example D8.

(B) Other Installations. Where feeder conductors have an ampacity greater than required by 430.24, the rating or setting

of the feeder overcurrent protective device shall be permitted to be based on the ampacity of the feeder conductors.

430.63 Rating or Setting

— Motor Load and Other Load(s).Where a feeder supplies a motor load and other load(s), the feeder protective device shall have a rating not less than that required for the sum of the other load(s) plus the following:

(1) For a single motor, the rating permitted by 430.52

(2) For a single hermetic refrigerant motor-compressor, the rating permitted by 440.22

(3) For two or more motors, the rating permitted by 430.62

Exception: Where the feeder overcurrent device provides the overcurrent protection for a motor control center, the provisions of 430.94 shall apply.

VI. Motor Control Circuits

430.71 General.

Part VI contains modifications of the general requirements and applies to the particular conditions of motor control circuits.

Informational Note: See 430.9(B) for equipment device terminal requirements

430.72 Overcurrent Protection.

(A) General.A motor control circuit tapped from the load side of a motor branch-circuit short-circuit and ground-fault

protective device(s) and functioning to control the motor(s) connected to that branch circuit shall be protected against

overcurrent in accordance with 430.72. Such a tapped control circuit shall not be considered to be a branch circuit

and shall be permitted to be protected by either a supplementary or branch-circuit overcurrent protective device(s).

A motor control circuit other than such a tapped control circuit shall be protected against overcurrent in accordance

with 725.43 or the notes to Table 11(A) and Table 11(B) in Chapter 9, as applicable.

(B) Conductor Protection. The overcurrent protection for conductors shall be provided as specified in 430.72(B)(1)

or (B)(2).

Exception No. 1: Where the opening of the control circuit would create a hazard as, for example, the control circuit of a fire pump motor, and the like, conductors of control circuits shall require only short-circuit and ground-fault protection

and shall be permitted to be protected by the motor branch circuit short-circuit and ground-fault protective device(s).

Exception No. 2: Conductors supplied by the secondary side of a single-phase transformer having only a two-wire (single-voltage) secondary shall be permitted to be protected by overcurrent protection provided on the primary (supply) side of the transformer, provided this protection does not exceed the value determined by multiplying the appropriate maximum rating of the overcurrent device for the secondary conductor from Table 430.72(B) by the secondary-to-primary voltage ratio. Transformer secondary conductors (other than two-wire) shall not be considered to be protected by the primary overcurrent protection.

(1) Separate Overcurrent Protection. Where the motor branch-circuit short-circuit and ground-fault protective device

does not provide protection in accordance with 430.72(B)(2), separate overcurrent protection shall be provided. The over

current protection shall not exceed the values specified in Column A of Table 430.72(B).

(2) Branch-Circuit Overcurrent Protective Device. Conductors shall be permitted to be protected by the motor branch-circuit short-circuit and ground-fault protective device

and shall require only short-circuit and ground-fault protection. Where the conductors do not extend beyond the motor

control equipment enclosure, the rating of the protective device(s) shall not exceed the value specified in Column B of

Table 430.72(B). Where the conductors extend beyond the motor control equipment enclosure, the rating of the protective

device(s) shall not exceed the value specified in Column C of Table 430.72(B).

(C) Control Circuit Transformer. Where a motor control circuit transformer is provided, the transformer shall be protected in accordance with 430.72(C)(1), (C)(2), (C)(3),

(C)(4), or (C)(5).

Exception: Overcurrent protection shall be omitted where the opening of the control circuit would create a hazard as, for example, the control circuit of a fire pump motor and the like.

(1) Compliance with Article 725. Where the transformer

supplies a Class 1 power-limited circuit, Class 2, or Class 3

remote-control circuit complying with the requirements of

Article 725, protection shall comply with Article 725.

(2) Compliance with Article 450.Protection shall be permitted to be provided in accordance with 450.3.

(3) Less Than 50 Volt-Amperes. Control circuit transformers rated less than 50 volt-amperes (VA) and that are an integral part of the motor controller and located within the motor

controller enclosure shall be permitted to be protected by primary overcurrent devices, impedance limiting means, or other

inherent protective means.

(4) Primary Less Than 2 Amperes. Where the control

circuit transformer rated primary current is less than

2 amperes, an overcurrent device rated or set at not more

than 500 percent of the rated primary current shall be

permitted in the primary circuit.

(5) Other Means. Protection shall be permitted to be provided by other approved means.

430.73 Protection of Conductors from Physical Damage.

Where damage to a motor control circuit would constitute a hazard, all conductors of such a remote motor control circuit that are outside the control device

itself shall be installed in a raceway or be otherwise protected from physical damage.

430.74 Electrical Arrangement of Control Circuits.

Where one conductor of the motor control circuit is grounded, the motor control circuit shall be arranged so that a ground fault in the control circuit remote from the motor controller will

(1) not start the motor and

(2) not bypass manually operated shutdown devices or automatic safety shutdown device

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VIII. Motor Control Centers

430.92 General.Part

VIII covers motor control centers in stalled for the control of motors, lighting, and power circuits.

430.94 Overcurrent Protection.

Motor control centers shall be provided with overcurrent protection in accordance with Parts I, II, and VIII of Article 240. The ampere rating or setting of the overcurrent protective device shall not exceed the rating of the common power bus.

This protection shall be provided by

(1) an overcurrent protective device located ahead of the motor control center or

(2) a main overcurrent protective device located within the motor control center.

430.111 Switch or Circuit Breaker as Both Controller and Disconnecting Means.

A switch or circuit breaker shall be permitted to be used as both the controller and disconnecting means if it complies with 430.111(A) and is one of the

types specified in 430.111(B).

(A) General.

The switch or circuit breaker complies with the requirements for controllers specified in 430.83, opens all ungrounded conductors to the motor, and is protected by an

overcurrent device in each ungrounded conductor (which shall be permitted to be the branch-circuit fuses).

The overcurrent device protecting the controller shall be permitted to be part of the controller assembly or shall be permitted to be separate.

An autotransformer-type controller shall be provided with a separate disconnecting means.

(B) Type.

The device shall be one of the types specified in 430.111(B)(1), (B)(2), or (B)(3).

(1) Air-Break Switch. An air-break switch, operable directly by applying the hand to a lever or handle.

(2) Inverse Time Circuit Breaker. An inverse time circuit breaker operable directly by applying the hand to a lever or

handle. The circuit breaker shall be permitted to be both power and manually operable.

(3) Oil Switch. An oil switch used on a circuit whose rating does not exceed 600 volts or 100 amperes, or by special permission on a circuit exceeding this capacity where under expert supervision. The oil switch shall be permitted to be both power and manually operable.

430.112 Motors Served by Single Disconnecting Means.

Each motor shall be provided with an individual disconnecting means.

-Table 430.52 Maximum Rating or Setting of Motor
Branch-Circuit Short-Circuit and Ground-Fault Protective
Devices

Note: For certain exceptions to the values specified, see 430.54.
1: The values in the Nontime Delay Fuse column apply to Time-Delay
Class CC fuses.

2: The values given in the last column also cover the ratings of non-adjustable inverse time types of circuit breakers

that may be modified as in 430.52(C)(1), Exception No. 1 and No. 2.

3: Synchronous motors of the low-torque, low-speed type (usually 450 rpm or lower), such as are used to drive reciprocating compressors, pumps,
and so forth, that start unloaded, do not require a fuse rating or circuitbreaker setting in excess of 200 percent of full-load current

;;;;;;

Table 430.247 Full-Load Current in Amperes, Direct-Current Motors
The following values of full-load currents
*are for motors running at base speed.

.........

Table 430.248 Full-Load Currents in Amperes, Single-Phase
Alternating-Current Motors
The following values of full-load currents are for motors running at
usual speeds and motors with normal torque characteristics. The volt
ages listed are rated motor voltages. The currents listed shall be per
mitted for system voltage ranges of 110 to 120 and 220 to 240 volts.

------

Table 430.249 Full-Load Current, Two-Phase
Alternating-Current Motors (4-Wire)
The following values of full-load current are for motors running at speeds
usual for belted motors and motors with normal torque characteristics.
Current in the common conductor of a 2-phase, 3-wire system will be
1.41 times the value given. The voltages listed are rated motor voltages.
The currents listed shall be permitted for system voltage ranges of 110 to
120, 220 to 240, 440 to 480, and 550 to 600 volts

......

Table 430.251(A)Conversion Table of Single-Phase Locked
Rotor Currents for Selection of Disconnecting Means and
Controllers as Determined from Horsepower and Voltage
Rating
For use only with 430.110, 440.12, 440.41, and 455.8(C).

-------

Table 430.250 Full-Load Current, Three-Phase Alternating-Current Motors
The following values of full-load currents are typical for motors running at speeds usual for belted motors and motors with normal torque
characteristics.
The voltages listed are rated motor voltages. The currents listed shall be permitted for system voltage ranges of 110 to 120, 220 to 240, 440
to 480, and 550 to 600 volts.

...........

--------

Table 430.251(B) Conversion Table of Polyphase Design B, C, and D Maximum Locked-Rotor Currents for Selection of
Disconnecting Means and Controllers as Determined from Horsepower and Voltage Rating and Design Letter
For use only with 430.110, 440.12, 440.41 and 455.8(C).

.........

NEC Example D8: Motor Circuit Conductors, Overload, Protection, and Short-Circuit and Ground-Fault

Protection (see 240.6, 430.6, 430.22, 430.23, 430.24, 430.32,430.52, and 430.62, Table 430.52, and Table 430.250)

Determine the minimum required conductor ampacity,

the motor overload protection,

the branch-circuit short-circuit and ground-fault protection, and

the feeder protection, for three induction-type motors on a 480-V, 3-phase feeder, as follows:

(a) One 25-hp, 460-V, 3-phase, squirrel-cage motor, nameplate full load current 32 A, Design B, Service Factor 1.15

(b) Two 30-hp, 460-V, 3-phase, wound-rotor motors, nameplate primary full-load current 38 A, nameplate secondary full-load current 65 A, 40°C rise.

Conductor Ampacity

The full-load current value used to determine the minimum required conductor ampacity is obtained from Table 430.250 [see 430.6(A)] for the squirrel-cage motor

and the primary of the wound-rotor motors.

To obtain the minimum required conductor ampacity, the full-load current is multiplied by 1.25 [see 430.22 and 430.23(A)].

For the 25-hp motor,

34 A × 1.25 = 43 A

For the 30-horsepower motors,

40 A × 1.25 = 50 A

65 A × 1.25 = 81 A

Motor Overload Protection

Where protected by a separate overload device, the motors are required to have overload protection rated or set to trip at not more than 125% of the

nameplate full-load current [see 430.6(A) and 430.32(A)(1)].

For the 25-hp motor,

32 A × 1.25 = 40.0 A

For the 30-hp motors,

38 A × 1.25 = 48 A

Where the separate overload device is an overload relay (not a fuse or circuit breaker), and the overload device selected at 125% is not sufficientto start the motor or carry the load,

the trip setting is permitted to be increased in accordance with 430.32(C).

Branch-Circuit Short-Circuit and Ground-Fault Protection

The selection of the rating of the protective device depends on the type of protective device selected, in accordance with 430.52 and Table 430.52.

The following is for the 25-hp motor.

(a) Nontime-Delay Fuse: The fuse rating is 300% × 34 A = 102 A.

The next larger standard fuse is 110 A [see 240.6 and 430.52(C)(1),

ExceptionNo. 1]. If the motor will not start with a 110-A nontime-delay fuse, the fuse rating is permitted to be increased to 125 A because this rating does not exceed 400% [see 430.52(C)(1), Exception No. 2(a)].

(b) Time-Delay Fuse: The fuse rating is 175% × 34 A = 59.5 A. The next larger standard fuse is 60 A [see 240.6 and 430.52(C)(1),

Exception No. 1]. If the motor will not start with a 60-A time-delay fuse, the fuse rating is permitted to be increased to 70 A because this rating does not exceed 225% [see 430.52(C)(1), Exception No. 2(b)].

Feeder Short-Circuit and Ground-Fault Protection

The rating of the feeder protective device is based on the sum of the largest branch-circuit protective device (example is 110 A) plus the sum of the full-load currents of the other motors, or 110 A + 40 A + 40 A = 190

A. The nearest standard fuse that does not exceed this value is 175 A [see 240.6 and 430.62(A)].