Motors overload as fuse

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hhsting

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Can fuses be used as overload only No short circuit ground fault over current protection for motors? 430.32, 430.33, 439.35 does not say it.
 
Fuses and breakers react differently than motor overloads. So, from my understanding, no you cannot use fuses as overloads.

Please correct me if I am wrong.


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hhsting said:
I dont get it. Post #1 question i dont see any reply
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Well, your sentence structure leaves a lot to be desired.
I think you’re asking if fuses can serve as ONLY OL protection, but not short circuit or ground fault protection.

In my opinion, the answer is no.
 
retirede said:
Well, your sentence structure leaves a lot to be desired.
I think you’re asking if fuses can serve as ONLY OL protection, but not short circuit or ground fault protection.

In my opinion, the answer is no.
Click to expand...

Correct. Ok. So then fuses can serve as OL and SC or GF protection or just SC or GF protection No OL for motors?
 
hhsting said:
Can fuses be used as overload only No short circuit ground fault over current protection for motors? 430.32, 430.33, 439.35 does not say it.
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Can fuses be used as OL protection? Yes, they can, in fact many people do that for smallish motors.

The problem is that fuses come in standard sizes, and the rules for motor protection require some relatively narrow protection limits, so finding the EXACT sizer fuse that you need to fit within those limits and still allow for not clearing on inrush gets increasingly difficult as you go up in size. But again, yes, people do it sometimes (especially OEMs looking to be as cheap as possible). The other problem is poses, especially for the end user, is that if the EXACT size fuse that you need is not available when your motor is down, then there is a tendency for people to just put in something larger that fits the fuse holder, or worse yet, a piece of pipe or a bolt.
 
My point is that if the fuse(s) is(are) sized properly as OL protection, they will be providing defacto short circuit and ground fault protection. At least for the portion of the circuit downstream of the fuse(s).

A lot of unknowns here, so YMMV.
 
retirede said:
My point is that if the fuse(s) is(are) sized properly as OL protection, they will be providing defacto short circuit and ground fault protection. At least for the portion of the circuit downstream of the fuse(s).

A lot of unknowns here, so YMMV.
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Agreed. I can't think of a scenario where the fuse is sized to provide proper OL protection but not SC and GF. This is before my 2nd cup of coffee, but I'll state that it's impossible.
 
hhsting said:
Correct. Ok. So then fuses can serve as OL and SC or GF protection or just SC or GF protection No OL for motors?
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  • You need OL, SC, and GF protection for motors, as specified in NEC.
  • Fuses (or any OCPD) can provide one or more of those functions.
  • It is often desirable to split the needed functions among multiple devices so that it properly protects the installation while also minimizing nuisance trips
 
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