Wiring 480 motor off 277 lighting contactor

[Tonythetiger]

I recently pulled 480v off the top of a 277 / 480 volt lighting contactor to run a couple fans, now one off the light circuits seems to be shorted, and trips the breaker, is this coincidence or wont it work correctly because these were 3 individual 277 light circuits?

 

[kwired]

Might be as simple as you added too much load to the existing circuit?

Might be starting current of motors is too high for existing overcurrent device?

If you have all three phases at the lighting contactor, you have what you need to run 480 volt single or three phase motor, whether existing circuit can take the added load is not easy to answer without more details.

 

[ptonsparky]

I recently pulled 480v off the top of a 277 / 480 volt lighting contactor to run a couple fans, now one off the light circuits seems to be shorted, and trips the breaker, is this coincidence or wont it work correctly because these were 3 individual 277 light circuits?

Various reasons.

#1 is you didn’t do it correctly.

We have no idea what sized motors. We do not know how big your breakers are. We do not know your lighting load. We do not know if you actually have the three phases at the contactor.

Most likely not not due to the 277 light circuits. Take the motors off.

 

[growler]

I recently pulled 480v off the top of a 277 / 480 volt lighting contactor to run a couple fans, now one off the light circuits seems to be shorted, and trips the breaker, is this coincidence or wont it work correctly because these were 3 individual 277 light circuits?

Take the motors off.

Are these three individual breakers supplying power to a three phase motor? You do understand that if one breaker trips it can let the motor single phase and burn up the fan motors.

I agree to take those motors off the contactor circuit.

 

[kwired]

Are these three individual breakers supplying power to a three phase motor? You do understand that if one breaker trips it can let the motor single phase and burn up the fan motors.

I agree to take those motors off the contactor circuit.

so can a blown fuse in other setups.

We need more details.

OP might have a three pole lighting contactor but for some reason have L1, L2 and L2 supplying the line terminals - three phase motor will always single phase if that is so. That is just one of many possible problems he may have with his setup.

 

[growler]

We need more details.

OP might have a three pole lighting contactor but for some reason have L1, L2 and L2 supplying the line terminals .

I agree that more details are needed.

He should be able to test for three phase with a volt meter. L2 to L2 will read 0 volts.

I'm suggesting that he would either need a three phase breaker or handle ties not only to protect the motor and for safety.

It would probably be hard to make this work legally.

 

[kwired]

I agree that more details are needed.

He should be able to test for three phase with a volt meter. L2 to L2 will read 0 volts.

I'm suggesting that he would either need a three phase breaker or handle ties not only to protect the motor and for safety.

It would probably be hard to make this work legally.

Motor needs overload protection regardless.

If small enough motor, it may be able to be on same circuit as the lighting, 1/2 HP 480 three phase motors only have FLA of around an amp, 10 HP around 12-14 amps, but may need a 25 or 30 amp breaker to allow them to start - that without additional lights loading the circuit.

If need to increase OCPD to allow for starting - now you possibly create code violations for the lighting part of the circuit.

 

[Tonythetiger]

These motors draw .5 amps, on a 20 breaker, tapped off top of lighting contactor to motor starter w/ appropriate overloads in place, i think i will just have to pull the wires in from somewhere else. I just wondered if it would affect the lights at all, being they were 3 separate
Circuits.

 

[kwired]

These motors draw .5 amps, on a 20 breaker, tapped off top of lighting contactor to motor starter w/ appropriate overloads in place, i think i will just have to pull the wires in from somewhere else. I just wondered if it would affect the lights at all, being they were 3 separate
Circuits.

May or may not have code issues with how you did what you did, but as long as you had all three phases involved there is no reason they shouldn't have worked if in proper working condition. Lights shouldn't have been effected either, they ultimately all tie to same three conductors before you get to the source anyway.

Did you try to run motor with lights off/lights with motor off?

Maybe you mis-wired the motor leads or have a ground fault somewhere in what you added?