vacuum pump motor replacement

[Mr. Serious]

I have a commercial customer I did some work for before. Last week they had the electric motor fail on their vacuum pump, and they searched online and found a new pump&motor combo unit that just bolts up to their tank. They have two choices, a 1HP unit that exactly replaces what they had, or a 1.5 HP unit.

1 HP 1-phase, 115/230 volts, 10.0/5.0 amps. Model number 7Z779
1.5HP 1-phase 115/230 volts, 15.2/8.2-7.6A. Model number 7Z782

Looks like the length, height, and inlet/outlet specifications match up well enough that either one could work.

Customer wants me to replace the pump, but also maybe add additional overload protection. I'm not sure what to do.

They have 3-phase power, 120/208Y. So, the original motor was running on 208 volts instead of the 230 it was rated for. The j-box at the motor location has two black #12 wires, but the circuit breaker is a 3-pole 30-amp breaker. I would want to at least change this to 20-amps. But is there anything else you would do? Should I plan on wiring the new motor for 115 instead of 230 because the voltage would match better? I probably would have to re-purpose one conductor as a neutral, all the way back to the panel. Or put a small auto-transformer?

And, is there anything else I should do to better protect the motor? The other thing I notice is that this room is very dusty. They have a vacuum pump and a compressor. The motors are inside a small closet where they are somewhat protected, but it's still dusty. The dust is probably what caused this to fail.

 

[ActionDave]

With 3 phase available I would look into changing to a new 3 phase motor.

If you stay with single phase it should run on 208V. That is what I would start with anyway. I'd go with the 1.5 hp either way. It shouldn't be a hard to get a new motor rather than a pump and motor, just match the frame number.

Changing to a smaller breaker won't do anything to protect the motor. The old motor likely died from neglect.

 

[Mr. Serious]

OK. I was supposed to post this on Thursday evening after I looked at the customer site, and I didn't take the time to do it until today, Monday morning. The customer just called again. They are ready to move forward with it, so they have ordered the 1HP motor and pump, the exact unit they had before. They will install it tomorrow, so my job will just be to go there on Wednesday and hook up the electrical. I told them I'd change it to a 20A breaker instead of 30A.

 

[drcampbell]

... The dust is probably what caused this to fail.

Not the undervoltage? Was the motor so caked with dust that it couldn't "breathe"?
Was this a premature failure? If not, there might be little point in looking for the cause.
A motor starter with appropriate calibration will protect the motor. They're not difficult or expensive.
I would also install a three-phase motor whenever three-phase power is available.
Make sure it's turning the right direction.

 

[Jraef]

You only need external OL protection if the motor is not "Thermally Protected", which should show on the nameplate.

If the motor is not specifically designed to run on 208V, what happens is that you lose torque, and that makes the motor have to work harder to do the job, thus increasing temperature and shortening its life. If you go with the 1-1/2HP motor, the added capacity of the motor can help compensate for that. That's how I would go if they are amenable.

 

[retirede]

You didn’t state what the vacuum application is, but if it’s a closed system, some pump designs can’t start will full vacuum on the inlet. If that the case, make sure the control that ensures unloaded starting is functioning properly.

If it’s just a vacuum cleaner, disregard the above.