Anyone care to size this mot...

[jamurr65]

Hi guys and gals, Im looking to replace the motor starter and overload for this motor its on a mid 1960s Saylor-Beall vertical air compressor. The motor is wired for 240 and I have it on a 40amp breaker. The wiring is temporary just to get it running to see if it pumps air so if it needs to change its no big deal.

 

[matt_i]

NEMA size 0 is good for 3hp @ 240vac. Make sure the one you get has coil voltage of 240vac. You will have to consult the chart for overload heaters unless you happen to find one with infinitely adjustable trip current.

You can probably find an IEC contactor for less (its smaller, not built like a tank) but will work. If you are testing why bother with the overload section. If it doesn't start, you switch off the voltage and don't let it sit there humming with a locked rotor.

 

[jamurr65]

It did start and run for about 5 minutes, everything seemed good pump and motor were very smooth and there was a big flash/arc at the contacts. Further investigation into the contacts, they are shot and looked like it had been doing this for a while...all black and burnt looking around the contacts.

 

[TRWham]

You'll probably need a NEMA size 1 for single phase 3 hp application, but check the rating for the particular starter you find. I would use a 2 pole DP starter like a Square D 8911. An 8911DPSG12V09 will work with B28 overload, but you may find it is easier to find a larger (30 or 40 A) 8911 starter for less money. I bought a new 40A 8911 for $135 on Amazon last year. If you apply a 3 phase starter with an electronic overload relay you will need to wire the overload so the current passes through all 3 legs otherwise it will trip prematurely. Heaters will not care.

If you ever lose that motor, I think you will find that 215 frame dual voltage motors are rather expensive for a 3 hp, and you'll probably want to consider a straight 240V (or spread 208-230V) 184 or 182 frame motor as a replacement. It will not impact the choice of starter but the mounting may need some rework.