Plus or minus voltage allowance for motor

[tld38]

Hi everyone! Have received many good comments in the past. I have a single phase exhaust fan for commercial kitchen. motor is 115/230-Capacitor start motor. 19.6 amps/9.8@230.Iwired for 115V. Ran #10,s Have 30 amp 2HP rated switches, One for disconnect@motor and one at hood. Voltage at panel is 114V. voltage at motor is 112V. voltage drop meets 3% allowance per NEC.(less than3.6V) This motor is fed from a sub-panel. I have 114V on phase A,118V. on phase B. Went to service and found same voltage from each phase. Amps=21.2 under load. I tried to look up model # under Granger supply to see if there is a plus or minus allowance for this motor. Problem is , Exhaust runs all day for customer, but at some point the integral thermal overload kicks out. Has to cool down, then can be re-started. Breaker never trips. I want to swap phases so motor will have specified operating voltage on nameplate. Motor is rated cont. duty with 1.15 SF. I,m thinking motor is bad. Company that installed this told me the problem is on my end. Thanks much!!

 

[John Valdes]

Could you have run 240 volts? Thats what I would have done.
Are you measuring the voltage with or without load. If the values above were taken without load you are to low for the load.

I agree with the motor manufacturer. Either get that low voltage where it needs to be (check transformer taps) or change to 240. Do you have 240 or 208? If you have 208, make sure the motor is rated for 208 and not 240. Some are rated for both. Be sure.

 

[stew]

check the current on this motor while in operation. if the current value does not exceed the nameplate rating then the problem is with the thermal or high ambient temp. All motors that are NEMA rated are rated to operate at rated temperature +/- 10% rated nameplate voltage. If this is a belt driven unit you may have a bearing problem,wrong pulley size etc. The current is the best way to tell what is causing your problem.

 

[hurk27]

I have found that many of these motors are sized right at the load of the fan/blower it drives without any head room, the slipage caused by just being 1 volt lower then the rated low voltage is enough to put it over current rating of the motor thus the reading of the 21.2 amps instead of the 19.6 FLA the name plate states. puting the motor on the higher voltage phase might bring this up enough to over come this but if the voltage drop of the circuit is high enough to drop below the 115 volt rating then other mesures would have to be made like buck boost or changing the circuit to 240 volts.

 

[stew]

what is the service factor on the nameplate? 1.0,1.15,1.25?

 

[stew]

sorry i just reread your post. at 1.15 service factor you should be able to see 22.5 amps without having the thermal tripping. sounds like a defective thermal to me.

 

[LarryFine]

Could you have run 240 volts? Thats what I would have done.

Absolutely, whenever possible, even if it means using a contactor.

 

[tld38]

Hi John! Thanks much for your comment. I posted another question regarding this motor. Thanks again!!

 

[tom baker]

If the motor and overload are not in the same location, use a ambinent temperature compenstated over load heater. this is especially important if the motor is in a very hot location.