Motor SCGF protection

[Jippy]

Help settle a discussion here. If a motor is fused with time delay fuses at the motor disconnect, this will provide motor short circuit protection. Must you still size your feeder circuit breaker in the panel at 250% of FLA due to the starting inrush current or must you simply match the time delay rating of the fuse?

 

[tony_psuee]

Re: Motor SCGF protection

Jippy,

The 250% is the maximum allowable size for an inverse time breaker by NEC, Table 430.52. You could choose a smaller size as a design consideration, but can not exceed that value unless you meet one of the exceptions.

Tony

 

[bphgravity]

Re: Motor SCGF protection

I personally would sized it to the maximum permitted to avoid any possible nuisance tripping.