120/240 compressor on 120/208 1Ø

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olly

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Berthoud, Colorado
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Master Electrician
I have a 120/240 single phase compressor that I need to wire into120/208 single phase. An old electrician mentor told me that motors are tough and that it wouldn't hurt it the motor. Does anyone object to that?
 
olly said:
I have a 120/240 single phase compressor that I need to wire into120/208 single phase. An old electrician mentor told me that motors are tough and that it wouldn't hurt it the motor. Does anyone object to that?
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The manufacturer might. The current would be appreciably more.

Look for the acceptable voltage range on the motor's nameplate itself.
 
The motor may be tough but it will run at the voltage limit per NEMA. Low voltage is more amps which is more heat, shorter life.
And the ac may not start, or start Unser pressure.
Does it have an unloader?
 
curt swartz said:
The motor uses a single voltage. If it can be wired for 120 or 240 you can connect it to 120 on the 208Y/120 system and it will care what the phase to phase voltage is.
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A motor for a 208 system is rated 200 v, a 240 system is 230 on the nameplate.
A really old motor is “220”
 
olly said:
I have a 120/240 single phase compressor that I need to wire into120/208 single phase. An old electrician mentor told me that motors are tough and that it wouldn't hurt it the motor. Does anyone object to that?
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I don't object. Most motors will run on the lower voltage. Look closely at the nameplate and see if it says something like "usable at 208V".
 
Compressors tend to run their motors to the actual limit. I would check my actual voltage and, if it's close to 208 and, as ptonsparky states, the compressor is critical, I would add a buck-boost transformer.
 
oldsparky52 said:
If it's not too far from the panel, I might just run it on 120V.
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At 1.5 HP it gets marginal to run a motor at 120V on a 20A circuit, 2HP it's maddening dealing with tripped circuit breakers. Before I upgraded to a 3 HP Rockwell Unisaw, I used a Delta contractors saw with a 1.5 HP motor wired for 120V, when doing a lot of ripping it would trip the breaker so plug it into another circuit & go back to ripping, it got tiresome but never changed the voltage, even though there was and still is the correct heater coil sitting in the starter can.
 
This discussion evokes a side question:

Why are dual-voltage 3ph motors rated at 208-230/460, but not 208-230/416-460? :unsure:

To wit:

1695860304169.jpeg
 
If 120/208 exists in the building, installing a 200-volt three phase motor on a 208-volt three-phase circuit seems like the obvious solution. It'll provide the best all around performance -- starting torque, simplicity, (no start switch, start winding or capacitor(s)) longevity, everything.


LarryFine said:
... Why are dual-voltage 3ph motors rated at 208-230/460, but not 208-230/416-460? ... :unsure:
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Because there are several million 208-volt services installed, and several dozen 416-volt? Motor manufacturers aren't aware of any compelling reason to rate their products for use on services that almost don't exist?
 
LarryFine said:
This discussion evokes a side question:

Why are dual-voltage 3ph motors rated at 208-230/460, but not 208-230/416-460? :unsure:

To wit:

View attachment 2567695
Click to expand...
Most 10hp motors or less have been usable at 208V since the last decade of the 20th century. I think manufacturers added the 208 to the nameplate to cut down on the number of calls to the help line.
 
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