SERVICE FACTOR
SERVICE FACTOR
(OP)
I have moticed exhaust fan motors with HP ratings from 2 on down with service factors of 1.35. I then see return and supply fan motors with a HP rating from 7.5 to 20 with service factors at 1.15. Is there a general rule for the service factor to be higher in motors with a smaller HP? Would the application be the case?





RE: SERVICE FACTOR
Mtr companies do derate like this. They could sell the same mtr as a 1.0 hp with a 1.15 sf. Get what I am saying? We are talking about production runs. With larger mtrs(400+) they give you the option of a 1.0 sf or 1.15 sf. Copper wire could be a major part of the cost in a larger mtr, but not so much in a smaller mtr. I could be proved wrong though, it may be application.
RE: SERVICE FACTOR
1HP down to 1/2HP SF=1.25
1/3HP down to 1/4HP SF=1.35
RE: SERVICE FACTOR
You are right, small motors are manufactured with higher Service factors (1.25 to 1.5 or larger) as compared to motors (2 HP and up), 1.0 to 1.15 SF.
The reason has to be the volume of materials involved and the cost reduction for massive production of reduced stock of designs covering a broader range of applications.
RE: SERVICE FACTOR
RE: SERVICE FACTOR
Compressors are another area they play with HP labeling. One I see a lot is the "5 HPSPCL" which is just a 3 HP motor relabeled as a 5 special.
RE: SERVICE FACTOR
RE: SERVICE FACTOR
I have always seen lower HP motors have a larger SF than a larger one (according to NEMA this is the case) but there is likely an exception somewhere.