Burning up single phase induction motors

Discussion in 'General Electronics Chat' started by truta11, Aug 12, 2014.

  1. truta11

    Thread Starter New Member

    Aug 12, 2014
    I recently had my pool pump motor fail. It's a 230 V single phase capacitor start motor on a Hayward Superpump II. I went to start it one day and it wouldn't turn, but would just hum. I couldn't find any faults with the centrifugal switch or the supply voltage, and the rotor turned freely by hand, so I changed the start capacitor. Changing the start capacitor made the motor turn briefly, then it returned to humming and then began to smoke. I don't know the exact age of the motor, but it probably has several years on it. I figured that its time had come and bought a new motor from the local pool store.

    The new pump was a knock off, a 1.5 hp labeled White River. The sticker on it indicated that it came wired from the factory for 230 V operation, and I double checked per the schematic on the housing. I'm fairly certain that I wired it correctly. Ground to the ground screw, one leg to the line 1 terminal, and the other leg to the line 2 terminal. Upon energizing the motor, it turned very slowly and noisily and then tripped the breaker, within 3 seconds or so. I checked the rotor and found that it turned freely, so I reset the breaker and tried again. Once again, it turned slowly and noisily and tripped the breaker, this time with accompanying smoke, and again within 3 seconds or so.

    I removed the pump and checked my supply voltage again. I checked both legs and the total voltage both before and after the breaker, both with the breaker on and off. I found everything to be correct, for no load at least. I had 240 volts total with 120 V in each leg both before and after the breaker with the breaker on, and no voltage after the breaker with it off. There was a switch in the circuit that would disconnect one leg to power off the motor. I did have phantom voltage present with the switch in the off position, but I assume that would disappear if I checked with a load present or with a low impedance meter, which I do not have. Since the switch only disconnected one leg, I removed the switch from the circuit for safety reasons and plan to replace it with a double pole switch to disconnect both energized legs when I turn the pump off.

    So here are my questions: I assume that there must be a problem with my electrical supply, that manifests itself only under load. Either that or I just got extremely unlucky. Unlucky happens from time to time. What could possibly cause two motors to get smoked on the same circuit after mere seconds of operation? How can I test the circuit under load to discover any such problems? I've thought of using 100 W lightbulbs in series, so that they drop 120 V each on a 240 V circuit, but that would be a purely resistive load. What else should I test to ensure that when I install my next replacement motor that it doesn't get smoked as well?

    Other information: The motor is on a 20 A 230 V GFCI circuit breaker made by Square D on a subpanel outside by the pool. The subpanel is on a 60 A 230 V breaker on the main panel in the house. As far as I know there are no junction boxes anywhere else in the circuit. I detected no shorts between the subpanel and the wire terminals that would connect to the motor.

    Thanks, and sorry for the long post.
  2. MaxHeadRoom


    Jul 18, 2013
    It sounds like you did everything right, you could try just the two 100w lamps in parallel on their own on the circuit to see if anything happens, voltage wise etc, but I suspect it will show OK.
    If the new motor had the Cap connected properly it should have ran OK.
    On a motor where the shaft is accessible, one test is to quickly give the shaft a spin and it should go into run if it is the cap or switch.