Running a 230 Volt single phase motor on 208 3 phase

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I have a End User of our Equipment having 208 3 phase added. The motor on the equipment is 230 V single phase. He wants to leave the motor as is and use the 208. My concerns are running the motors under voltage drawing to much current and when running the motor not running to full capacity. Should this be done?
 

Besoeker

Senior Member
Location
UK
I have a End User of our Equipment having 208 3 phase added. The motor on the equipment is 230 V single phase. He wants to leave the motor as is and use the 208. My concerns are running the motors under voltage drawing to much current and when running the motor not running to full capacity. Should this be done?
I suppose it depends on the motor loading. If it isn't running close to its maximum rating, you might get away with it on 208V. But bear in mind the 208V supply will have tolerance limits and if you are at the lower end of that limit the 230V motor would have to cope with very significant undervoltage.

If the motor is 230V, single phase it probably isn't very big. How much would it cost to replace it with a motor rated for the proposed voltage and avoid the risk/uncertainty?
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
I have a End User of our Equipment having 208 3 phase added. The motor on the equipment is 230 V single phase. He wants to leave the motor as is and use the 208. My concerns are running the motors under voltage drawing to much current and when running the motor not running to full capacity. Should this be done?

We have some customers that are doing this. The supply voltage is 215-218. Motors have been running fine for a couple of years. You need to know what the delivered voltage is before making a final decision.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
I don't think it would be a problem for most fractional HP motors like this either. But if it is more than a motor, IE a machine with a control system relying on a transformer for control circuit power that might need addressing.
 

kwired

Electron manager
Location
NE Nebraska
I would agree with HvLv,
I have seen enough 230V motors run on 208V that I would not be overly concerned.

Same here - as long as motor is not sized right at required horsepower of the driven load or if supply voltage is not at lower end of tolerance range of 208 volts it will probably be fine.
 

Rick Christopherson

Senior Member
One thing to consider, is that if it is a dual voltage motor, you would be well served to reconfigure it for 120 volt operation. Then it will receive its rated voltage.
 

hurk27

Senior Member
I have run into problems with high torque applications such as air compressors did one as instructed by the owner and the motor lasted a whole month before it burned up, even though the overloads or over current protection didn't trip it still took out the motor, so all I can say is to make sure you cover it in a disclaimer in your billing or you could end up buying a motor, and keep in mind there is no room for any voltage drop.

A motor design to run on 208 will have a 200 VAC rating.
 

broadgage

Senior Member
Location
London, England
It will probably be OK especialy if the nominal 208 volt supply is on the generous side.

Could be a problem though in hot conditions, or of the motor is heavily loaded, or if the 208 volt supply is actually only about 200.
 

ramsy

Roger Ruhle dba NoFixNoPay
Location
LA basin, CA
Occupation
Service Electrician 2020 NEC
208 boost.gif
Exhibit 210.17 Circuitry for an autotransformer used to derive a 240-volt system
for appliances from a 208Y/120-volt source, in accordance with 210.9, Exception

Taken from 2005 NFPA-70 Handbook
 

kwired

Electron manager
Location
NE Nebraska
A very basic, long term, inexpensive way to fix the problem.

For common sized fractional hp motors - may cost as much as motor. I generally say let it run as long as it may run, and replace with motor rated to operate on 208 volt when time comes. (It seldom seems to come BTW).
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
For common sized fractional hp motors - may cost as much as motor. I generally say let it run as long as it may run, and replace with motor rated to operate on 208 volt when time comes. (It seldom seems to come BTW).
I agree, but would expand the criteria to include more than fractional HP motors.

I have seen plenty of pump and compressor motors 1 to 5 HP 230V that run a long time on 208V. Starting switches fail more often than any thing else. I will add that our voltage is always around 215V.
 

kwired

Electron manager
Location
NE Nebraska
I agree, but would expand the criteria to include more than fractional HP motors.

I have seen plenty of pump and compressor motors 1 to 5 HP 230V that run a long time on 208V. Starting switches fail more often than any thing else. I will add that our voltage is always around 215V.

Same here. My point was that using an autotransformer to correct voltage may cost just as much or even more than replacing a small motor, maybe even up to about 2 hp.

I run into problems with starting switches or capacitors more often on 240 volt systems than I do on 208 volt systems. Probably has more to do with the fact there are more single phase motors on single phase systems than there is on 208 volt systems.
 

Besoeker

Senior Member
Location
UK
Same here. My point was that using an autotransformer to correct voltage may cost just as much or even more than replacing a small motor, maybe even up to about 2 hp.
That's what I was getting at in post #2.
Replacing the motor also has the merits of fewer bits and fewer connections.
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
Reading the posts in this thread, and many others on this forum; there is a lot of time and effort spent on finding ways around a particular problem. In most cases, including this one, I think one only has to ask themselves:

Is the equipment rated for the installed use and conditions.

In this case, and often times, no. Therefore, you have two options here. Provide the properly rated motor, or provide the proper voltage to the motor you have. From a good engineering perspective, these are the only choices.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Think about what is entailed in replacing a single phase motor with a three phase. New motor, new starter with overloads, disconnecting means, more wires even if they are smaller. Talk about added parts to fail. A buck boost requires no more than what is already there for the original motor. Just hook it up. Nothing special. Longevity would be similar to any transformer.

Most of the time I do not worry about it, other than informing the owner and giving them the options, but if the demand on the motor is heavy a properly sized BB is an easy long term fix.
 
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