motor short circuit /grd fault

[papa]

A while back I did a job as directed by employer that I have questioned whether it was code complyent.

3 , #6 thhn c. ran from a 60 amp 480 volt breaker , with # 10 grd.to a 60 amp N/F disconnect , tapped in a trough to # 10 ran to 4 manual motor starters ,then on to 4, 3 hp 3 phase motors. See anything wrong?

 

[ptonsparky]

I think it will depend on the manual motor starters. Did they provide short circuit protection?

 

[papa]

I think it will depend on the manual motor starters. Did they provide short circuit protection?

no, only thermal overload protection

 

[augie47]

430.52 would require a 15 amp breaker or a 10 amp fuse as the maximum GF-SC protection.

 

[Jraef]

430.52 would require a 15 amp breaker or a 10 amp fuse as the maximum GF-SC protection.

Yep. If they are NEMA style thermal only manual motor starters, then you must "group fuse" them as augie47 says.

Most of the IEC style MMS units are already UL listed for group fuse installations all by themselves because they have the short circuit instantaneous trips built-in. That may be where they got the idea, but it sounds like they extended the concept to something not suitable for use like this.

 

[mull982]

Yep. If they are NEMA style thermal only manual motor starters, then you must "group fuse" them as augie47 says.

Are you saying that one fuse can provide the short circuit protection for all 4 motors as opposed to having a fuse or short circuit protection for each of the 4 motors individually? Is this mentioned in 430.52?