Correct Capacitor Size?


Jun 24, 2011
Indio, CA
The cap on my Pentair 2hp SF 1.3 pump went bad. The repair company replaced the 35uf with a 30uf 370 VAC.

The cap is under the hump on top, so I guess that's a RUN Capacitor.

I have read online NEVER replace with one of lesser value as it could result in overheating, but its ok for one value higher .

and also

The motor engineers have done extensive testing on their products to determine the capacitor that is the most efficient for that particular motor. Under no circumstances should one substitute a capacitor larger than the original Our testing with over rated capacitors caused the motor to severely overheat and could result in a fire hazzard and or destruction of the motor. If you must in a dire emergency attempt to substitute a run capacitor, try to use one that is as close to or lower in mfd value than the original...Never install one that is a higher mfd value than the original.

and also

Run capacitors are designed for continuous duty, and are energized the entire time the motor is running. Single phase electric motors need a capacitor to energize a second phase winding. This is why
sizing is so critical. If the wrong run capacitor is installed, the motor will not have an even magnetic field. This will cause the rotor to hesitate at those spots that are uneven. This hesitation will cause the motor to become noisy, increase energy consumption, cause performance to drop, and cause the motor to overheat.

Before I contact them, I need to know did they screw-up? Or screw me? Which answer is correct?

I don't want to prematurely damage the pump or cause a fire. I live in the desert (120º), so the pump is already Dang hot from the sun.
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Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
I think your capacitor is fine. 30 vs 35 uf is not a big difference.

You don't cite where you copied that stuff about capcaitors from but I believe it is comments about industrial motors and not specifically pool pump motors.

@JamesW thoughts?


TFP Expert
Mar 2, 2011
Typically, you want to use the same exact uF rating. It might be ok because it's pretty close. I don't think that it's going to be a problem, but I would prefer to have the exact right one.

Bama Rambler

Mod Squad
TFP Expert
Bronze Supporter
LifeTime Supporter
Jun 22, 2009
SouthWest Alabama
Mfg's take into account the 10% variance in capacitor tolerances, so a 35mfd can be anywhere from 31.5mfd to 38.5mfd. and a 30mfd can be pretty close to the lower number if it's at rating or above. However, if it's 10% low then it's out of the mfg capacitor rating at 27mfd. If they tested the capacitor with an actual capacitance tester (which I always recommend even on new caps) and it showed 30mfd or above, then it's fine to use. If it showed less than 30mfd I would change it at my earliest convenience.