Lets share @ElectroStores.org

And that is the determining factor in the first place…the premise we work from.

Let’s start with the worst one: PSCC (Prospective Short Circuit Current):-

If it has been determined that our new panel is rated the same or higher then the PSCC at that point of the installation than we are halfway there.

This must have special consideration the closer we are to the main distribution transformer to the site…even more so in an industrial environment.

Now the easier one: Current carrying capacity of all the conductors. The cable feeding our panel has to have over current protection (the correct overcurrent) protection.

And this is the crux of the matter: Everything downstream from this cable must also be protected, thus if you intend to use smaller wires for whatever reason in the panel…a circuit breaker (fuse) is the only solution.

If those smaller wires start from the entry point of the panel so be it…a circuit breaker is required.

If only the control wires will be smaller than an isolator is adequate and only the control wires be protected by a circuit breaker (fuse).

And so the confusion is addressed because all codes/regulations dictate that all panels must have an isolator…this is the minimum requirement.

If it so happens that the required circuit breaker also qualifies as an isolator then we got happiness…two flies with one stone.

Please note: An isolator has minimum requirements in terms of safety. It has much to do with the mechanical connections and the distances of the contacts when in OFF position, so PLEASE confirm that the circuit breaker qualifies as an isolator AND the correct type of isolator for the application.

It is required by the standards that a symbol be printed on the product to indicate its function(s). See here for symbols.