I have a situation at work with a 10hp 600 volt motor driving a centrifugal pump. The 1.15 service factor of the motor allows us 125% for overload heater values, but can I continuously operate the motor at 125% of its nameplate value? In this case nameplate current is 9.4 amps, so 125% is 11.75 amps. The discharge valve of the pump is throttled back because wide open causes the motor to draw beyond its nameplate value. Thanks.
I could be wrong but from what I have understood in the past the "service factor" is the percentage the motor can be overloaded for a SHORT DURATION without causing damage to the motor.. So really that motor will put out ( 10 * 1.15)= 11.5 horsepower ( 15% overload) for a short duration with no damage to the motor.. The overload heater being at 125% of nameplate FLA is just a MAXIMUM value of the setting of the overload heaters, not the percentage of how much you can overload the motor..
BTW, some overload heaters allow for the 125% rating.. you just size them to what your motor FLA is and thats it...should say somewhere on the overload or starter somewhere..
I pulled this definition from my old Cox's Electricians Guide to AC Motor Controls: service factor- the number by which the horsepower rating is multiplied to determine the maximum safe load that a motor may be expected to carry CONTINUOUSLY at its rated voltage and frequency." Just curious if there any other thoughts out there.
I picked up a handbook just now .. " IPT's electrical Handbook" and it says:
"Multiplying nameplate power by the service factor reflects how much the motor may be overloaded, PREFERABLY for brief periods"... So I guess you could overload the motor continuously but it would shorten the life of the motor, as it is technically being run in an overloaded condition??!!