max rating of non-time delay fuse

[holiday]

is a 20 amp fuse the correct max rating of the initial non-time delay fuse for the branch -circuit short-circuit protection of a 1 hp 3 phase 208 volt squirrel cage motor

 

[George Stolz]

Re: max rating of non-time delay fuse

My guess: Since a 208 3? squirrel cage motor is rated by 430.250 (NEC-2002 430.150) at 4.6 amps, and per table 430.52 you fuse it at 300%, giving us a total of 13.8 amps.

A 15 amp fuse would be the more proper choice, in my barely educated opinion.

 

[kiloamp7]

Re: max rating of non-time delay fuse

Curious why you would use a non-time delay fuse for this. Why not a modern, time-delay fuse at appx. 175% ?

 

[tom baker]

Re: max rating of non-time delay fuse

A non time delay fuse often results in a larger fused disconnet, nusiance tripping, and they are hard to find. I'll size a time delay fuse at 125% or so.