I have a air compressor that runs of 3 pole breaker. Recently, I changed motor, 230-460v, but after wiring?

Question

It, it just trips breaker. I checked all volts to the three wires, all at 120, but once connected, volts drop. Why?

Answer 1

Okay, you need to make sure you wired the 3 phases in the correct order and on the correct taps in the motor. It might say 230-460v but a motor needs to have multiple connection options to achieve that range. If you mixed up the wires it could trip the breaker. You might even have damaged the motor in that process.

If you misswire a compressor, and it runs backwards it will damage the compressor. It may have a protective design that trips the breaker before this can happen.

Inside your panel starting from the top breaker is A phase, next down is B phase (both breakers left side to right side) Then C then A then B then C. It's possible that your breaker is not positioned to align with ABC in that order. It might be CAB or BCA. Inside the motor you should have L1 L2 and L3 which need to be ABC.



Also you mentioned nothing about wattage or amperage.

Are you sure that your motor is not too powerful for the circuit? If so, don't just change the breaker. Your wire might be too small for more amps.

Wattage/voltage = amps. Your voltage is not 120 to the motor, it operates on the 3 phases together so you need to measure between two phases to get the actual voltage. You might only have 208v, which is typical for 3 phase systems (even though the single phase voltage is 120).

Normally that wouldn't trip a circuit though. But being under-powered will increase the amp draw which could explain the trip. The nameplate on the motor should have a range of volts and Kw. Power stays the same no matter what voltage. To find amps, do [kW x 1000/V] You normally rate the breaker at least 125% of whatever the actual max amps for your particular configuration is (but not higher than the closest typical amperage).

In other words, if the nameplate says 7.8kw then do 7800/230 (=33.9). So if the motor draws 34 amps, then you need at least 42.5 amps, so you would have a 50 amp breaker and number 8 THHN if it's in conduit, or number 6 if it's romex or UF.



(it's obviously not a wye system, not that it matters, because you read 120 from each phase to ground... in a wye system, the center phase is the neutral so there is no voltage to ground. A delta system has 3 true phases and an isolated neutral.)

Answer 2

Have a qualified professional electrician service the installation. Either the wiring in the motor is for a different voltage or the breaker has a problem. It could be worn out or the wrong size for the new motor. From your description you have a 208/120 volt system.

Answer 3

Silly question, but are you sure you're running off a three-phase panel and that your 3-pole is hitting all three phases? Some residential three-phase panels have slots where you don't get true three-phasing. Did you change the existing motor from 230 to 460 by installing a new transformer or was it already pre-enabled by jumping or reconfiguring? If you reconfigured existing, are you SURE you reconfigured correctly?

Answer 4

You have 120 to center tap or phase to phase? If it's phase to phase, I've sure never worked with it. I dunno what the heck you have. It sure looks like a 3 phase, 4 wire wye. Check phase to phase and let us know. At least then I can tell if you have a wye or delta config. Wye should show 277 to ground and delta will show 0 depending on if it is tapped or not. I suspect you've gone 1-3-2 or some other permutation. Let us know what you have phase to phase (it should be 480) and phase to ground (277 or 0).



Just tell us phase to phase voltage and phase to center tap voltage. Right now it sounds like 120/208Y.