ISA/FSA info....

[mrcaptainbob]

I have a 240 motor that I'd like to know the amps draw. (This is different than the motor on the waste oil furnace...). It has two call outs, the first is ISA 10.5 and the second is FSA 11.5. Since I can see no other 'amps' info, I presume these to be the amps reading, the smaller number is the running load, the larger is the starting load. Am I correct in assuming that that's the total amps draw for both legs? So it's actually (to start) 11.5/2 amps per leg? (5.75A)

[HayZee518]

is that isa and fsa information in the amps box? fla means full load amps, lra is locked rotor amps. normally a motor that starts draws 130% more than name plate amps, then settles down as its rated speed is reached. I looked in a Baldor engineering spec sheet and didn't see anything related. what type and manufacturer is the motor? can you submit a picture of the nameplate data?

[mrcaptainbob]

Motor info....

Hmmm, this error could either poor spelling on my part, or just a bad memory from the barn to the house! I do believe you are correct, HayZee. That does answer my question, but I'll post a picture later. One more thing.....would that amp load be across both legs? That is, each leg draws half of that load? Thanks for the help. Again.

[HayZee518]

the amp draw on any leg would be the same, not halved. a single phase 240 volt motor operates on two phases, each 180 degrees out of phase with the other, so theoretically the amps in each winding would be zero. each pole shift would cancel the other but because it happens so fast, 120 times a second you will read fla on each phase or wire. in the case of a three phase motor, you have a reversal occurring every 120 degrees of a full cycle of 360 degrees. because it occurs three times per cycle, you need a correctional value which is the cube root of 3 which is 1.732. if you took a three phase motor apart and connected it to a three phase source and turned it on and placed a ball bearing inside the stator, the bearing would rotate along the stator iron, trying to catch up to the rotating field.
any motor MUST satisfy a complete cycle of 360 degrees. the sinusoidal waveform that you observe on an oscilloscope starts at a zero reference, goes up to ninety degrees, then down to the zero reference or 180 degrees, then below the reference to 270 degrees and back up to zero or 360 degrees, a full cycle.