120/208V 3 Phase to 120/240V Single Phase
- Thread starter smithjo30
- Start date
- Occupation
- Licensed Electrician
Check the nameplate on the motor, there's a good chance it will say Usable At 208V.
To confirm, you're saying I could wire it as 3 phase 208V anyways?
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Or buck/boost transformer if it is not.
- Location
- Illinois
- Occupation
- retired electrician
No. It is a single phase motor, but a 240 volt motor may be suitable for operation at 208 volts.
No. If the motor says 230V, or 208V-240V on it, it could be powered by 208V/1P from the 208V/3P panel. It may run hotter and slower, however.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Says 115/208-230, so you can run it on the 208 you have.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
That nameplate was not from an OP, it was just an example of how a nameplate marked to indicate that the motor may be run on 208V 2-wire.
Cheers, Wayne
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Good point, Wayne. (I really shouldn't post before the coffee has hit.)
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
It shouldn't run slower, speed still based on frequency and number of poles in the motor. It will draw more current for same output load than it does if supplied by 240 volts.
Depends on the application. In theory it won't slow when just running with no load, but with load the increased slip can cause your motor to slow down, as well as heating up to the point where your windings are damaged. V=I/R, but there are more variables involved than just those.
I had a client want to hookup a straight 240V (Meaning nameplate ONLY said 240V) motor to 208V and test to see how it would go before converting a whole facility. The motors held up, but the production line was a few % slower, which caused all kinds of issues with their processes due to the timing of other functions. Ultimately, they decided it was best to replace the 240V motors with 208V-230V/460V to modernize as well as allow for future changes.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
V=I*R
Yikes, that's an embarrassing typo. Thanks.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I suppose depends on the application is true. Most general purpose ~1800 rpm motors are not normally slowing down, they just going to draw more current in order to do the same work. If running them at full output rating that is likely going to shorten life of the motor from the extra heating. If they have a service factor over 1.0 and you are not loading over rating that probably helps some but technically they are still overloaded to some extent.
If specifically marked 208-240 volts on nameplate they are designed for either, still will draw more on lower end of that rating, but likely will have a range in the nameplate amps to match upper and lower voltage rating as well.
A motor that has more of a limited duty cycle or is lightly loaded will likely last longer as well compared to one that runs continuously or near full rating for long periods.
So yes depends on the application.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Typical induction motors run slightly below synchronous speed, and if you drop the voltage than the motor will slow down slightly.
So a 4 pole motor running on 60 Hz will have a synchronous speed of 1800 RPM. This speed is a constant function of AC frequency and motor poles.
Under full load and full rated voltage, that motor might operate at 1750 RPM, meaning a 'slip' of 50 RPM. Slip is a non-linear function of load and applied voltage. Drop the voltage a 10% and the slip might increase to 55 or 60 RPM, for a new operating speed of 1740 or 1745 RPM. If you drop the voltage you can expect the motor to slow down at least slightly.
-Jonathan
So a 4 pole motor running on 60 Hz will have a synchronous speed of 1800 RPM. This speed is a constant function of AC frequency and motor poles.
Under full load and full rated voltage, that motor might operate at 1750 RPM, meaning a 'slip' of 50 RPM. Slip is a non-linear function of load and applied voltage. Drop the voltage a 10% and the slip might increase to 55 or 60 RPM, for a new operating speed of 1740 or 1745 RPM. If you drop the voltage you can expect the motor to slow down at least slightly.
-Jonathan
I'm.old school and have seen 240 volt single & three phase motors operate on 208 volts but like I .posted in an earlier post had customers that ran 240 volt motors on 208 volts but they had a shorter life span due to hot summer days where I often only measured 190 to 192 volts at load side of starters. On one search somebody recommend a maximum of 6% +/- on motors so a 240 volt motor even if marked suitable for 208 volts should never operate below 225.6 volts. If it was me I would install a buck boost transformer. They do not cost that much.At the hospital that I worked at several installs that were connected to 208 volts caused some kind of problem where company would not honor warranty until we jnstalled a buck boost transformer to raise the voltage close to 240 volts.