Motor Branch Circuit Protection

[mstrlucky74]

So the branch circuits are to be protected against short circuit, ground fault and overload. Breakers or fuses protect against the SC & GF. I'm not clear on what protects against overload. I read somewhere that the overload is located in the motor controller or it's integral to the motor.

1. What's the motor controller?
2. Would the thermal toggle switch below be considered overload protection?
3. Would the combo starter disconnect be considered overload protection?
4. Are all motors required to have overload protection in one form or another?

https://www.schneider-electric.us/e...sible-disconnect-switch-combination-starters/

https://www.grainger.com/product/1H...f6NJqMq8jDof_QYq1LHhQtmnSkKBRt1caAvsUEALw_wcB

 

[infinity]

So the branch circuits are to be protected against short circuit, ground fault and overload. Breakers or fuses protect against the SC & GF. I'm not clear on what protects against overload. I read somewhere that the overload is located in the motor controller or it's integral to the motor.

1. What's the motor controller?
2. Would the thermal toggle switch below be considered overload protection?
3. Would the combo starter disconnect be considered overload protection?
4. Are all motors required to have overload protection in one form or another?

https://www.schneider-electric.us/e...sible-disconnect-switch-combination-starters/

https://www.grainger.com/product/1H...f6NJqMq8jDof_QYq1LHhQtmnSkKBRt1caAvsUEALw_wcB

1- A starter or VFD would be two examples.
2- Yes.
3- Typically yes.
4- Almost all, as an example I don't think that a clock motor requires it.

 

[mstrlucky74]

1- A starter or VFD would be two examples.
2- Yes.
3- Typically yes.
4- Almost all, as an example I don't think that a clock motor requires it.

Thanks. For continuous duty motor you size the conductors to 125% of the FLC table 430.248 or 250. Once you get the ampacity you don't use the 310 section table, you use a table in 430 for conductor size?

 

[ActionDave]

Thanks. For continuous duty motor you size the conductors to 125% of the FLC table 430.248 or 250. Once you get the ampacity you don't use the 310 section table, you use a table in 430 for conductor size?

Where is there a conductor ampacity chart in art 430?

 

[mstrlucky74]

Where is there a conductor ampacity chart in art 430?

I guess there isn't one. Was just going off top of my head from what I thought I remember reading in past. Maybe it was the OCPD I was thinking of.

 

[ActionDave]

I guess there isn't one. Was just going off top of my head from what I thought I remember reading in past.

There's not.

You use the tables in 430 to get your conductor ampacity and to size your ground fault/short circuit. You use 310.15 for your wire sizes 99% of the time. You use the nameplate on the motor to size your overloads.

 

[infinity]

Dave's reference basically sends you to T310.15(B)(16). For motor circuits be aware of 240.4(D).

 

[mstrlucky74]

There's not.

You use the tables in 430 to get your conductor ampacity and to size your ground fault/short circuit. You use 310.15 for your wire sizes 99% of the time. You use the nameplate on the motor to size your overloads.

Got it. I thought nameplate was also used for the OCPD(breaker etc.)

 

[infinity]

Got it. I thought nameplate was also used for the OCPD(breaker etc.)

No, nameplate for overload protection, the tables in the NEC for conductor size and OCPD size.

 

[mstrlucky74]

No, nameplate for overload protection, the tables in the NEC for conductor size and OCPD size.

ty

 

[Jraef]

That particular toggle switch does NOT have an OL heater in it. You CAN get ones that have it, but that one does not.

All motors must have protection from overload. SOME small (typically fractional HP) motors come with built-in thermal overload protection so the control device, such as that toggle switch, do not need to provide it externally. IF the motor has thermal overload protection, it MUST state it on the nameplate, usually using the words “Thermally Protected”, or sometimes abbreviated as just “TP”, or words / abbreviations to that effect. It that is not CLEARLY designated or readable on the motor nameplate, you must assume it needs external.

On small things like the aforementioned clock motor, it will often say it is “impedance protected”, which means it can be totally stalled and not be overloaded.

 

[mstrlucky74]

That particular toggle switch does NOT have an OL heater in it. You CAN get ones that have it, but that one does not.

All motors must have protection from overload. SOME small (typically fractional HP) motors come with built-in thermal overload protection so the control device, such as that toggle switch, do not need to provide it externally. IF the motor has thermal overload protection, it MUST state it on the nameplate, usually using the words “Thermally Protected”, or sometimes abbreviated as just “TP”, or words / abbreviations to that effect. It that is not CLEARLY designated or readable on the motor nameplate, you must assume it needs external.

On small things like the aforementioned clock motor, it will often say it is “impedance protected”, which means it can be totally stalled and not be overloaded.

Thanks.