Motor service factor

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john d

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Is it ok to run a motor in the service factor? I have a motor with a name plate rating of 7.8 amps. It is set up on the load correctly and runs 8.6 amps. Is it ok to run a motor like this?
 
If the service factor for this unit is 1.15 you are just below the maximum. Running a motor using the service factor will accelerate the rate at which the insulation will age by a significant amount. Thats not to say that the unit will fail rather quickly ,just that it will fail faster than if it were below those levels. One question would be is what is the type of laod on this and is it continous?Does the motor cycle and therfore have the time it needs to cool? As long as you dont let the smoke out of the case you are good to go lol.. Joe
 
Increase the horsepower or if it is a belt driven unit you can change the pully size to slow down the blower to bring your current down. Is this a three phase motor and what HP and service factor?
 
The motor is a 3 HP 3phase with a 1.15 service factor running on 240v. The name plate shows 7.8 amps at 240v. The nec 430-250 indicated 9.6 amps. Does table 430-250 already add in a service factor? We size our wire for 430-250 then add 25% i thought for voltage fluxuations, but if it is legal according to the nec to run in the service factor our wire size should be amps + S.F. + 25%.
 
Being a motor shop guy for over 18 years I have often wondered why the NEC tables never seem to match most manufacturers nameplates. I think the have taken nameplate ratings from several manufacturers and averaged them.They dont take a rating and add 15 % or in some cases 20 or 25 % to get the table figures. Unless someone on here was on that codemaking section we may never know how its derived. You are required by code to multiply the table amounts by 1.25 to get your minimum current ampacity. If you want to add 15% first and then multiply by 1.25 so much the better but it is not required by code.
 
john d said:
This is what we got after the air balancing was done to get the correct amount of air. [CFM]
Click to expand...

Maybe at one time someone adjusted the air flow so the motor would not be overloaded. Now it is back to the original value. I would run motor until it quits (if you can afford downtime when it quits) and plan to replace it with larger motor, maybe even have motor on hand to reduce down time when it does quit. Otherwise I would plan to replace soon.

If motor is in airstream it will probably last longer than if it is not in airstream.
 
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