breaker size for pump

[jrfbuildit]

I could use help in trying to size a proper breaker for a residential sewage pump. I was told by the plumber that the motor has a "start spike" of 29 amps and the running amps are around 5.8 to 6 amps. The pump is thermally protected. Where in the NEC can I find proper sizing of the breaker for this pump. (on a side note, the variation between the start amps and running amps seems broad to me. I would think that the start amps would be closer to 19 or so but I'm going by the plumbers word.) Thanks.

 

[suemarkp]

Article 430 for motors. Take the FLA and max breaker size is 250% of that unless it turns out to be too small (i.e. it trips on start up). Most motors (ones not under a huge load when starting) will be fine on a breaker sized at 125% of the FLA (which is what the wires get sized to). Even at 250%, you're just barely looking at a 15A breaker which is the minimum for a branch circuit so it is still allowed.

Don't worry about the start spike. Breakers will ride through most of those. You could probably put 29A through a 15A breaker for a few minutes before it would trip its thermal element.

 

[ActionDave]

The long answer is art. 430.31. The short answer is a 15 or 20A branch circuit will be fine.