Breaker sizing

[pmason0]

So installing a new compressor, 5 hp 3 phase, the motor shows amps 15.4-14.7 would a 20 amp enough or should I bump it up to a 30 amp breaker? Is there a normal % of head room you should have?

Maybe we should have some stickies be created for general rules, see the other thread on how many outlets per breaker is a good rule of thumb.

 

[mayday0017]

Doesn't sound like a real 5hp motor to me... Not sure what braker to run either as I know little to nothing about 3 phase

5hp is typically 20-25ish amp (roughly)

 

[Aceman]

I'd start with a 20 amp breaker. I always go 125% of the NEC motor HP tables, and then pick the next size up breaker.

The tables say 15.2 amps for a 240 3 phase motor x 125%=19 amps

 

[pmason0]

Aceman, thanks, that was what I as thinking, rounding up, going up the 20 thinking it was 15.2.
mayday, as I understand 3 phase motors are less amperage as they are to be more efficient.

 

[Stuart in MN]

Doesn't sound like a real 5hp motor to me... Not sure what braker to run either as I know little to nothing about 3 phase.

A 230vac three phase 5hp motor has a full load amp rating of about 15.2 amps.

Personally, I'd go with a 30 amp breaker, 20 amp is cutting it a little close. [I have a page out of an old Square D circuit breaker catalog with recommended trip ratings that I use as a cheat sheet.]

 

['04 Cummins]

With an inverse time circuit breaker (standard breaker), max overcurrent protection is 250% of full load current, then increase to next standard size (NEC Table 430.52). 15.2 x 2.5 = 38, so actually max breaker would be 40 amp, though I would go with a 30.

 

[mayday0017]

A 230vac three phase 5hp motor has a full load amp rating of about 15.2 amps.

Learn something new every day, I know nothing about 3 phase

 

[930dreamer]

X2 on the 30 amp. I started two 5 hp 3 phase motors(loaded) together and the amp clamp showed 142 amps for a second.

 

[pmason0]

Thanks for all the feedback, just ordered the 30amp, damn those 3 pole breakers are expensive.