Motor on wired for wrong voltage.

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arnettda

Senior Member
Will a motor wired for 120 volts run with 240 volts applied to it? The motor is dual rated. I have a customer that replaced a pump motor in his hot tub. He said the spa store bench tested it and it ran. He installed it and it runs but makes a horrible noise. It is a Loud growl or rumbling noise.Not a locked rotor hum noise. The motor spins and draws roughly 64 amps on each phase. It is 1.5 H.P. motor. I could not remove cover to see if it was wired correctly with out draining the tub.
 

arnettda

Senior Member
Did you change the winding connection for 120V (actually it will be 115V)?

I did not try to run the installed motor on 115v only the 220 volts that supplied it from the control board. I was unable to get to the motor dog house or wiring terminal to see if it wired right without removing the motor.
I could use a test cord and see what it does on 115 volts. I did not think of this when I was there.
 

Besoeker

Senior Member
Location
UK
Will a motor wired for 120 volts run with 240 volts applied to it? The motor is dual rated. I have a customer that replaced a pump motor in his hot tub. He said the spa store bench tested it and it ran. He installed it and it runs but makes a horrible noise. It is a Loud growl or rumbling noise.Not a locked rotor hum noise. The motor spins and draws roughly 64 amps on each phase. It is 1.5 H.P. motor. I could not remove cover to see if it was wired correctly with out draining the tub.
I can see that being terminal, no pun intended.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
Will a motor wired for 120 volts run with 240 volts applied to it? The motor is dual rated.
No. It will smoke.
I have a customer that replaced a pump motor in his hot tub. He said the spa store bench tested it and it ran. He installed it and it runs but makes a horrible noise. It is a Loud growl or rumbling noise.Not a locked rotor hum noise. The motor spins and draws roughly 64 amps on each phase. It is 1.5 H.P. motor. I could not remove cover to see if it was wired correctly with out draining the tub.
Is it a two speed motor? Connecting the high and low together will have this effect.
 

arnettda

Senior Member
I have to agree with both.
Owner drained hot tub and pulled the motor. It was wired for wrong voltage. Wired it for 240V and worked all right when we bench tested it with water in the pump. I will let you know if motor fails soon.
 

arnettda

Senior Member
I take you did not try and run for very long the first time. If it didn't smoke or smell bad when it was wired up wrong it might be alright. Magnet wire can be pretty resilient in the face of adversity.

No, roughly only a minute or until to much water started to run out of the pump.
 

robertmorkel

Member
Location
India
1) The motor will run slower.
2) The torque developed will drop to about 25% of its full voltage rating.
3) This decrease in torque can make the motor stall when trying to start under a heavy load.
4) There may be drastic speed fluctuations due to load variations.
5) The motor current will double if the load remains constant.

I can understand how these issues could cause severe problems in some applications, but perhaps not in the application I am looking at. I want to use a squirrel cage motor rated at 1/20 HP, 240 volts, 0.5 amp in a direct drive fan application.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
If you run a motor at double its rated voltage, then it will draw a _huge_ amount of magnetizing current.

The increased magnetizing current will cause huge bearing loads and will make the motor sound really bad. There are probably also magnetic effects that directly make noise as well. The bearing loads will quickly (but not instantly) lead to bearing failure.

The increased magnetizing current will cause the wind temperature to rise very quickly. If the winding temperature is allowed to get too high, the magnet wire insulation will fail. Again this is _not_ instant.

If you catch the problem quickly, then the motor will likely survive the experience.

Robertmorkel, you are asking about a different situation, a motor operated at half rated voltage. For a properly sized fan load, this may not be a problem. Fans do not require much starting torque and are nice steady loads. The biggest issue is to make sure that the current drawn by the motor is less than or equal to the rated full load current.

Note: the torque of the motor does not drop when you reduce the supply voltage. Rather the _peak available torque_ will drop. The actual output torque will depend upon the applied load and the (now modified) torque/speed curve of the motor.

-Jon
 

kwired

Electron manager
Location
NE Nebraska
such fan motors as suggested are often PSC or shaded pole motors - they intentionally lower voltage to such motors for speed regulation purposes. When such a fan has less speed it demands less torque so input current is naturally lower to begin with. The synchronous speed of the motor doesn't change if the frequency remains the same. By supplying it with undervoltage it allows for more slip because there isn't enough torque to keep it at/near synchronous speed though.
 

kwired

Electron manager
Location
NE Nebraska
Owner drained hot tub and pulled the motor. It was wired for wrong voltage. Wired it for 240V and worked all right when we bench tested it with water in the pump. I will let you know if motor fails soon.
Chances are it will survive, may have taken a little off total life but nothing too significant, especially if it has internal thermal protection, and many of these small single phase motors usually do.
 
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