230 volt motors on 208V?

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olc

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I know it is an old question.
Bldg will have 208V.
The owner is buying some 230V-3ph equipment. The equipment has motors (and heat in one case).
Best bet to size a 208X240 transformer for the 3 items (or one transformer each)?
Or run on 208V?

208X240 transformers are not common. Use a 240X208?
 
olc said:
I know it is an old question.
Bldg will have 208V.
The owner is buying some 230V-3ph equipment. The equipment has motors (and heat in one case).
Best bet to size a 208X240 transformer for the 3 items (or one transformer each)?
Or run on 208V?

208X240 transformers are not common. Use a 240X208?
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Check the nameplates for operating frequency.
 
Not much experience with straight 230V motors running on 208V, what I saw was problems. They were reefer truck compressors on a long (500'+) run of wire with no upsizing for voltage drop. That building had 480V so there were more options to correct the problem.

I think most xfmrs 15kva or larger can be back-fed w/o problems. You'll want to see if you need a neutral on the 240V side.
 
olc said:
I know it is an old question.
Bldg will have 208V.
The owner is buying some 230V-3ph equipment. The equipment has motors (and heat in one case).
Best bet to size a 208X240 transformer for the 3 items (or one transformer each)?
Or run on 208V?

208X240 transformers are not common. Use a 240X208?
Click to expand...

There's about an eightyfive percent or better chance that your motors are either rated for 208V or will run on 208V. Most motors in the last twenty years are made to run at either 240V or 208V. Also a 230V motor on a 208V system where the actual voltage is around 215V is within operating range.
 
How close the motor is loaded to it's rating can have some impact here also. Many cases I'd say just connect it and it will probably last a very long time. If it is something that is constant load and near motor rating - maybe better think about it harder. If a general purpose type motor that is easy to replace with what is needed, either replace it or have one ready for when you do toast the existing motor. If it has 1.15 SF but not running into SF for load - it probably still lasts a long time.
 
kwired said:
How close the motor is loaded to it's rating can have some impact here also. Many cases I'd say just connect it and it will probably last a very long time. If it is something that is constant load and near motor rating - maybe better think about it harder. If a general purpose type motor that is easy to replace with what is needed, either replace it or have one ready for when you do toast the existing motor. If it has 1.15 SF but not running into SF for load - it probably still lasts a long time.
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Pretty much my thoughts, but we're not working on his CYA application. For us, the 208 most likely runs on the high side and would be in the operation range of the plus/minus 10% for the motor.
 
ptonsparky said:
Pretty much my thoughts, but we're not working on his CYA application. For us, the 208 most likely runs on the high side and would be in the operation range of the plus/minus 10% for the motor.
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The part that makes me a bit leery also is that the OP says the owner is “ buying some equipment”.

Not knowing how old, what condition, and how hard will it be to find replacement motor for the equipment would make me cautious.
 
NEMA has a motor spec +/- 10% on voltage. Overvoltage for a motor above 10% saturates the windings and the current increases. So a low supply on a 208 volt system may get you in trouble. New motors are dual rated 200/230.
 
jumper said:
The part that makes me a bit leery also is that the OP says the owner is “ buying some equipment”.

Not knowing how old, what condition, and how hard will it be to find replacement motor for the equipment would make me cautious.
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Or where from. The 230V, non standard for you, ought to be considered.
 
208V is right at the bottom end (-10%) of supply voltage specs of a 230V motor; anything significantly less than 208V will cause problems. Straight-rated 230V motors (not 208-230) are made for a 240V system anyway, accounting for voltage drop at the service and on customer wiring giving ~230V at the equipment. Yes, a 'hot' (higher than nominal) voltage on a 208V service, say 216V, and conductors sized for very little (3% or less) voltage drop at the motor's FLA will probably work ok, but if your install has 205V at the panel and with VD you have 197V at the motor, especially one that cycles a lot, is running at its maximum load, or have a long run of minimally sized wire feeding it, you are going to have problems.

If you have a transformer in there somewhere, depending on what other loads are coming from your panel, you might be able to adjust the taps to get closer to 230V rather than buying a step-up transformer.
 
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