FLA vs SFA

[ILCML]

on a (for example) 2HP 3phase 208-230/460v motor data sheet, it has 'none' listed under the SFA, would it be because they didn't test for it, or it's the same as the FLA? I can't imagine why they wouldn't list it. I couldn't get an acceptable answer out of the reps I deal with, and would rather get your opinions anyways.

 

[DickDV]

Sounds like a motor with a 1.00 service factor

 

[ILCML]

I thought the same, but was told that the SFA is NOT equal to the FLA x SF, that there was more to it than a simple calculation...

 

[waross]

If no figure is given I would assume a service factor of 1.
From the Cowern Papers on the Baldor Motor site

Service Factor Amps
This is the amount of current the motor will draw when it is subjected to a percentage
of overload equal to the service factor on the nameplate of the motor. For example,
many motors will have a service factor of 1.15, meaning that the motor can handle a
15% overload. The service factor amperage is the amount of current that the motor
will draw under the service factor load condition.

http://www.baldor.com/pdf/literature/PR2525.pdf

respectfully

 

[jraef]

NEMA MG-1 does not require SFA to be on the nameplate. Service Factor, yes, but only if it is over 1.0. So if there is no mention of SF or SFA, then the motor is a 1.0SF. Either that, or it is an IEC design, and there is no such thing as Service Factor in the IEC world. Doubtful though in your case because it would be unusual to see a 208V rating on an IEC motor.

Service factor is supposed to be a temporary overload capability. Many motor manufacturers are reluctant to put SFA as a separate parameter on the nameplate because users have interpreted that as an endorsement of running a motor into the SF on a continual basis.

 

[ILCML]

thank you guys!

 

[rovineye]

There can be a relationship between SF and ambient rating as well. A motor may have a 1.15 SF at 40 Deg C, and the same motor could be rated at 1.0 SF at 50 Deg C ambient. Same motor design, just differnt nameplates depending on application.

 

[aolalde]

Service factor(SF) applies to output power (HP).
The current at SF load is related to the efficiency(EFF), power factor(PF) and line voltage(Vll). Note that EFF and PF change with every change of load. Then:

SFA = SF*HP/[SQRT(3)*Vll*EFF*PF]

For exact calculation of current, the EFF and PF curves vs Load for the specific motor are required.

 

[friend81]

suppose if that motor has a 1.15SF then the SFA can also be 15% more than the FLA or is there any other calculation?

(Thanks ILCML actually i was about a start a thread for a same kind of query regarding relation between SFA & SF%)

 

[jraef]

aolalde just gave it to you!