208 volt rewire to 220

[derbuechsenmacher]

I have a new to me series 1. The motor us presently wired for 208v 3ph. I will be using a VFD to get my 3phase. I’ve not been able to find anything about changes to the motor to be able to use 220 instead of the current 208 it is set for. Any suggestions

 

[MyLilMule]

I am not an electrician.

But (I did stay at a Holiday Inn Express once) from what I have gathered myself, there is no difference to the motor wiring for low voltage 3 phase situations (240/220/208) and only would need to be changed for high voltage (480v).

It has to do with the phases of each leg. Single phase 240 is two 120 volt legs that are 180 degrees out of phase. The difference in potential between the two 120 volt legs is 240 volts.

3 phase is 120 degrees out of phase. And although each leg is 120 volts to neutral, because they are 120 degrees out of phase, the difference in potential is not 240 volts. The difference in potential between one leg and the next is only 208 volts.



It's a bit more complicated than that and a some of it is over my head. But this was the best explanation I was ever given.

Bottom line, there's no change to the motor. I've never used a VFD before, so there may be something that needs to be done there to adjust the voltage to 208? I don't know if it would even be necessary.

I don't make any assertions that any of this is correct and am open to feedback from those much more qualified than me on where I am wrong.

 

[Ulma Doctor]

There is no need to change anything.
A 208 motor will run on 220 or 230v..
If you are putting a VFD on the mill, the VFD will control voltage , amperage, and frequency.
As long as you set the VFD’s parameters correctly, your motor will operate as intended without further modification.

 

[rabler]

I believe a 230 volt VFD will allow you to enter the motor's nameplate voltage, i.e., 208 volts, and will adjust it's output accordingly. They have to derate the RMS voltage when under 60Hz for correct operation, so running a 208V 3 motor on a VFD with a 240 input will work OK if the motor voltage and amperage are entered into the VFD.

edited: @Ulma Doctor types faster.

 

[Ulma Doctor]

P.S.
208V is a transformer output , usually used in industrial settings

 

[benmychree]

As I understand it, it is OK to run higher voltage on 208 V motors up to 240 V, the amps drawn under higher volts will lower under the same loads.

 

[Dabbler]

Run it for a while. If you have heating problems, then you can add an autotransformer to change the voltage. this is a mod that you should only do if you run into problems. It will cost$$$ and takes a bit to do it, but it is quite easy - the *second* time you do it....

 

[Ulma Doctor]

Do not add a transformer between the VFD and the motor, magic smoke will come from the VFD

 

[Dabbler]

Do not add a transformer between the VFD and the motor, magic smoke will come from the VFD

You are 100% right. But:

An autotransformer (or 3, actually) does NOT interfere with the operation of the VFD. This is the solution that the TECO folks gave me for fixing a similar problem. The motor amperage has to be adjusted to the correct (different) value. It is a last resort thing when you get motor heating due to high loads and over current due to the voltage difference.

As I said in the above post - only if you have motor heating problems is this worth it.

 

[Ulma Doctor]

If the transformer(s) is(are) supplying the VFD , i would agree .
The VFD directly controls the motor without other input or output