Motor Fuses/430.42

[Jay_Gatz]

I'm being told that I can run a 2HP 480V motor on a dedicated 15A circuit with an unfused starter with appropriate sized overloads per 430.42. My understanding would be that I would still need to follow 430.52 for max overcurrent protection and fuse the motor at 3.4 x 1.75 = 5.95A. Does 430.42 override 430.52?

 

[tom baker]

Every motor requires overload protection and branch ckt protection.
Fuses are not required for branch ckt, short ckt and ground fault protection, but they offer better protection, IMO,than a ckt breaker. It depends on the cost of the motor, how critical it is as to fuses or cb.

 

[Jay_Gatz]

So I'm allowed to protect it with a 15A breaker even though it's way higher than dictated by 430.52?

 

[tom baker]

I need to look at Art 430 before I answer

 

[Dennis Alwon]

So I'm allowed to protect it with a 15A breaker even though it's way higher than dictated by 430.52?

I say it is allowed

430.52(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 short-circuit 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.

 

[augie47]

I agree with Dennis. The fact that 430.52 allows "next size up to standard values" and 240.6 shows 15 amps as the lowest standard breaker size allows you to do so. For "better' protection a lot of folks would prefer fuse protection with smaller fuses listed in 240.6 as standard.

 

[tom baker]

My Square D Motor Data Calculator shows a 15 amp thermal magnet breaker, and per Augie and Dennis its allowed.
Personally I prefer fuses, but you have to keep spare fuses of the correct size on hand. with a dual element TD fuse I can be sized slightly above the overload setting, and of course fuses are available in many more sizes than breakers.
Remember this, "the breaker protects the wire and the overload protects the motor. the breaker is correctly called the branch circuit, short circuit and ground fault protection device, in a short the current will be very high the breaker, even at 15 amps will open immediately.

But again its what do you want to spend to protect the motor? May not be cost effective to rewind a 2 hp motor.

For some good information on motor protection (and biased) refer to the Bussman Fuseology info https://www.eaton.com/content/dam/e...cal-literature/bus-ele-br-10757-fuseology.pdf

 

[don_resqcapt19]

240.6 is going to add 10 amps to the standard sizes of OCPDs in Table 240.6 in the 2023 code. Availability of 10 amp breakers may become an issue for circuits like this

 

[tom baker]

I almost added that some mfgs have 10 amp CBs, I have used 10 amp QOs from Square D

 

[don_resqcapt19]

I almost added that some mfgs have 10 amp CBs, I have used 10 amp QOs from Square D

yes, I have used them for PLC I/O power, but typically not a stock item for the supply houses we used.

 

[Jay_Gatz]

I appreciate everyone's help, I'm going to still push for a starter with fuses in it but I can now see that it is acceptable to just use the 15A breaker.