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switched electric motor spontaneously comes on when switch is off

switched electric motor spontaneously comes on when switch is off

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  #1  
Old 08-02-11, 04:42 PM
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Question switched electric motor spontaneously comes on when switch is off

I've been using this switch to control my swimming pool electic pump since we bought the house used twelve years ago. This week (shortly after a heavy storm) the pump started coming on while the switch for the pump was turned off. The pump starts, works for 15 seconds or so then acts like there has been a power dip and slows down, then the motor stops and hums. The only way to stop it is by using the circuit breaker in the house's main electrical box. I opened the switch box outside and inspected it. It is an aluminum outdoor box. There was some white powdery corrosion but not all that much. Switch looked OK, no evidence of arcing. So, I replaced the switch. No change to the problem. I don't get how the power can get past the switch to turn on the electric motor. It's like a one horsepower motor. I thought it was 220, but when I removed the switch I found it to be 110. Now, I'm stumped and not sure what to do next. I only have a couple days to deal with it before the swimming pool will go sour and I'll have 20,000 gallons of green water. Any ideas what I should do in order to diagnose the problem. I do have another electric pump as a spare for the pool. I have not installed it yet because I doubt that the electric pump is the problem. However, I can install the backup pump if you think it is worthwhile to do so. I'm clueless as to what to do next.
 
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  #2  
Old 08-02-11, 06:02 PM
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Are you sure it is not wired 240VAC? The pump could have been wired 240, with only one of the legs switched off. If that is the case, there could be a short somewhere between the switch and pump going to ground and letting 120VAC pass through to the pump.
 
  #3  
Old 08-02-11, 09:18 PM
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Are you sure it is not wired 240VAC? The pump could have been wired 240, with only one of the legs switched off. If that is the case, there could be a short somewhere between the switch and pump going to ground and letting 120VAC pass through to the pump.
But then when he would turn the switch on it would trip the breaker.
 
  #4  
Old 08-03-11, 12:34 AM
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OK, those two suggestions are helpful. There is another box next to the one that has the switch. The power also goes to that box which is unused. It's for a pool light that has never worked since we have been here. I'll open the other box and see if it has water in it or any evidence of a short. I'll try to rule out a short there, too. Thanks and I'm still workin' on figuring out where there may be a short with the ground wire. I appreciate both posts from caddymac and Justin Smith. Any additional posts will be appreciated. Thanks!
 
  #5  
Old 08-03-11, 05:47 AM
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Originally Posted by Justin Smith View Post
But then when he would turn the switch on it would trip the breaker.
Yes, in theory. If there is enough impedance in the fault, the breaker may not trip.
 
  #6  
Old 08-03-11, 10:59 AM
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I honestly don't think that if it's not enough to trip the breaker that it would be enough to start (let alone sustain) the motor.
 
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Old 08-03-11, 11:43 AM
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The OP says it began after a storm so I would be looking for an electronic control, maybe a timer.

Don't know if it is time for a radical solution yet but if I had the problem I would probably make a diagram of existing wiring, remove the wiring, and wire from scratch with new parts and wire.

IMHO sometimes fixed is more important then why.
 
  #8  
Old 08-03-11, 12:10 PM
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Thanks Ray, I appreciate your input. There's no timer or other electronic contol devices that I'm aware of. I'm going to work on it later today. First I'm going to check out the ground wire in both outside boxes. They are both on/off switches but I think the ground is shared between the two switchs. There is one other unused outlet inside for that circuit. It is a 220 circuit but the switch that was in there is for only 110. The line goes through the brick back wall of the garage, then to the two outdoor boxes and a leg over to the old pool light that does not work. I'll post up again after I check these little things. I like your idea about fixed is more important than why. That's especially true when there's twenty thousand gallons of water that will get nasty in a few more days lol.
 
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