Conductor size calculation- Motors

[595sparky]

I'm a 4th yr app. and I have questions about conductor sizing Using 430-150 ,430-52 (min. amp.x125%) and Table 430-52. When calculating maximum rating of branch-circuit short-circuit devices when starting current is an issue do conductors need to be sized to values obtained using 430-52?( NOT TO EXCEED)

 

[iwire]

Re: Conductor size calculation- Motors

Hi Sparky.

I am not sure if I understand what you are asking here.

But it sounds to me you are asking if you need to size the conductors to the short circuit ground fault protective device.

If that is the question the answer is no.

430.52 is only for finding the size of the Motor Branch-Circuit Short-Circuit and Ground-Fault Protective Device.

Conductor sizing is based on the tables in the back of 430.

It is possible to be code compliant and have conductors connected to breakers that are rated much less than the breaker size.

An extreme case could have 14 awg on a 60 or 70 amp breaker.

The motor overload devices protect the conductors from being overloaded.

If that is not what you where asking sorry.

Bob

 

[eric64]

Re: Conductor size calculation- Motors

Motor branch circuit conductors are sized using articles in part II of 430. 430.21 for example states branch circuit conductors shall have an ampacity of not less than 125% of the motors full load current(Table 430-150). Table 430.52 is used only for the rating of short circuit and ground fault devices. There are exceptions to the values in table 430-52 that pertain to upsizing the device to account for a higher starting current. This only applies to the device and not the conductor sizing. Hope this helps