I am just installing a 5 Hp 1750 RPM 220 DeVair compressor and the Baldor motor amp rating is 23. Does this mean that it consumes 23 amps running? I was wondering what amperage it might draw at startup. Is a 30 amp breaker adequate for this machine?

The general rule for motors is 1.25 x FLA for circuit ampacity. It will possibly draw 6x as much current during startup but the time-current curve of the breaker should handle that unless there are specific instructions that would overrule.

According to the Canadian code ( its the same as yours ) the proper wire size is for 30 amps so a # 10 will do but rule of thumb is to go 1 size up so a #8 is better . But for a single phase all types motors a 60 amp circuit breaker is required .
If the compressor is controled by a pressure switch on repeated starts it is starting against a head pressure and will draw more current plus as the motor heats up it also will draw more current

Dan

A 30 amp breaker should work fine. To answer your question, yes, the Baldor motor will pull 23 amps when the driven device (air compressor) is taking 5 HP. Inrush currents can be very high on startup, but most magnetic circuit breakers will handle it fine. If the compressor isn't using all 5 HP, current draw will be less.

Couple of things: make sure you get a breaker with a common internal trip (usually says so on the steel bar connecting the toggles). Also, circuit breakers aren't designed to be switches. I know too many people who use the circuit breaker to turn their air compressors on and off. Works in a pinch, but after too much abuse they'll either fail early or won't trip when they're supposed to. Either let the air compressor do the cycling, or get another form of disconnect between the breaker and the compressor. Magnetic starters (aka contactors) are the best way to go, but a cheap Square D nonfused disconnect works just fine too.

-Dave

Thanks for the info. I have a mag starter and a isolation switch and I am going to put in a 50 amp. breaker as I have room in my panel.

The 50 amp will allow some component meltdown before it kicks, in my opinion. RonW

Amp ratings on circuit breakers aren't like horsepower - more isn't necessarily better. A circuit breaker's job is to prevent short circuits and overloads, which lead to fires. You only want to go with an amp rating that is as high as the largest draw on the circuit. Since you will be running a 23 amp motor, (basically the same as a 25 amp motor), you wouldn't want to put in a 25 amp breaker because you're running the ragged edge. Chances are just as good that the breaker would trip than hold. So, you go one size up, to a 30. This means you can draw your 25 amps with no nuisance trips, but will also prevent your _properly-sized_ conductors from becoming a fire hazard if you were to develop a short circuit at the compressor, or anywhere after the circuit breaker.

If you go with a 50 and the motor becomes overloaded or stalled (if the bearings seize, for instance), it will sit there and smoke and may even start on fire, and your breaker will never trip. This isn't what you want, either.

What gauge wires are you running for this motor, by the way? I would suggest 10 AWG at the minimum. (Wire sizing IS like horsepower, however - bigger is better.)

-Dave

Wire is #10 and is stranded rather than solid. Compressor will always be turned off when no one is around. Other compressor which I have had for 23 years is on a 60 amp fused switch by the panel and was installed by an electrician. Needed a second compressor for more air for glass beading and sandblasting. I wondered at first if I could run both off the fused switch, but if they both came on at the same time, then fuses would blow due to start up loads. So I looked at the panel and there is room for a 220 breaker and I had a spare 50 amp so it should work. Thanks for the imput.

To use the 50A breaker and not have fire hazard will require #8 Cu wire.

The circuit breaker protects the motor and the wire. 50A breaker will not adequately protect the motor unless there is a seperate overload device.

.......motors. Wire size must have an ampacity greater than the breaker's rating. Set the 50A breaker aside, JMO, Rod.

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1957 C-600 Cab-over carhauler w/390-4V, 2-speed rear-end
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MCGC member #75

"There will ALWAYS be an FE in my LiFE"

"Compressor will always be turned off when no one is around". It may be turned off when you are not around, if you do not forget. But the world does not work that way. You have to plan for it to always be turned on when nobody is around. You have to plan on a line breaking so that the compressor runs indefinately trying to keep up. Do that, and you might be safe. Nice to use the stuff you have lying around, but a 30 amp breaker is about fifteen bucks. It is just asking for it to go bigger.

The guys are right, over-sizing the breaker is not good- it's job isn't to NOT trip, it's to trip at an increased, abnormal load. I'd also suggest changing out the 60 amp on the other compressor to the appropriate size-especially if it's 23 years old and has worked quite a bit. I'm fortunate, as my friend runs the warehouse of a large local electrical contractor, have quite a few sparkys to draw on. The big Ingersol compressor is on a 30, the 3-phase Bridgeport and big South Bend lathe are on 30's with static phase converters, two 50 amp welder-only outlets, and 20 amp 110's all around the shop. BTW, three-phase stuff can be a great deal- mills, lathes, and such that don't start under load work pretty well with an inexpensive static converter, just a little down on power, and compressors can be converted to single phase- I got a great deal on the good Ingersol T-30 ($200) as it was used-cherry but 3-phase, found a new Baldor 5hp single phase motor on epay for $175 and bought one of the "rectal itchin's" lunch and a case of beer, I switched out the motor, and he put in the new box, breaker, pulled the wire, and re-configured the starter to single- about 2 hrs. time

Just make sure your insurance is up to date and that it covers everything in your shop when it burns down.

You asked and these guys gave you good advice. If you choose to ignore it then be prepared to suffer the consequences. It really is that simple.

Doug
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Size the wire to the motor.  Size the breaker for the wire. Over loads protect motors. Breakers protect the wire. Breakers are not an on/off switch/overload protection and were never designed to be one. John

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