Motor disconnect and feeder protection device sizing

[rowelelectrical]

Hi..

Can anybody advise how can i size motor disconnect and feeder protection device? the motor size is 10HP.3PH,208V. Im getting confused in sizing it as per short circuit and ground fault protectiion, overcurrent and overloading.:-?

 

[don_resqcapt19]

Conductor sizing per 430.22, short circuit and ground fault protection per 430.52, and overload protection per 430.32.

 

[jim dungar]

Hi..

Can anybody advise how can i size motor disconnect and feeder protection device? the motor size is 10HP.3PH,208V. Im getting confused in sizing it as per short circuit and ground fault protectiion, overcurrent and overloading.:-?

Is this a circuit to a single motor?
Are you using breakers or fuses?
Are you using a motor controller with an overload relay (i.e. does it use heaters or thermal units)?
Where is your 'disconnect' in relation to your motor controller?

 

[poeboy]

there are many more factors involved, not just voltage & HP.

Distance from the source voltage, type of wiring method used, type of OCP, Service factor of the motor, Too many for my brain to recall them all.... the ones I listed above are just the most important to me.

If I recall most 10 HP @ 208 instead of 240 delta makes a major shift in conduit, wire, and OCP sizing.


then the nameplate ratings of the motor can be very different than what the code guidelines are in addition to keeping code in mind. The nameplate ratings are essential for final hook ups and settings. ....

This may help you make a decision.

http://www.electrician2.com/calculators/motor_ver_1.html

 

[augie47]

Take note from 430.6 that you use the Tables (in your case 430.250) for sizing everything except separate overload protection for which you use nameplate. Then follows Dons' instructions in Post #2.
Once you determine your values, if you would like a second look, post your values here.

 

[hbendillo]

Is this a fusible disconnect?

 

[jumper]

I would look at Example D8 in Annex D. It is for two motors, but the principles and code sections can be used for one.