One Circuit Multiple Motors

[mkgrady]

I need to wire three 2 HP motors with one circuit available to serve them. The motors and circuit are three phase 480 volts. The circuit is #12 wire on a 20 amp breaker. FLA of each motor is 2.7 so the circuit appears to be large enough. The motors will not be run continuous. These motors will be protected against overload by way of the starter heaters. Will the starters also protect against short circuit and ground fault? Or do I need to use fused disconnects at the motors and fuse them at 250% of FLA for each motor? How do I fuse at 6.75 amps? NEC 430 has so much in it. I could use some help with this. Thanks

 

[Dennis Alwon]

Some overloads are capable of ground fault or short circuits. Look at 430.40

 

[augie47]

It will make little difference, but note that for other than selection of overload devices, the value in the Tables is used for other calculations, so your 2 HP motor at 480 volts would be figured at 3.4 amps. Your maximum GFSC device for a Inverse time breaker would be 15 amp, or for a dual element fuse 6 amp.
If your overload device does not incorporate GFSC protection, you would need to comply with the above for the maximum fuse or breaker.
You might also note any manufacturers instructions that accompany your overload device as they often list a maximum fuse for protection of that device.

 

[mkgrady]

Thank you Dennis and Augie. Very helpful

 

[Cow]

I've used some sweet little din rail mount manual motor protectors from Allen Bradley and Eaton that work great for this.