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Thread: Resistance Check on a Pool pump Motor

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    Resistance Check on a Pool pump Motor

    What should the reading be (just approximate) on a good pool pump motor when measuring resistance/ohms? The motor is 230V single phase. I don't know much about motor types so all I know is that it is for a pool pump. It is a US motor brand.
    If you aim at nothing, you will hit it every time!

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    Depends on the motor type. Start windings can be twice that of the run. In the low ohms. Assuming single phase. Winding to winding should be in the Megaohms. Windings to ground in the mega to giga ohms. What do you have?
    Tom
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    Quote Originally Posted by ptonsparky View Post
    Depends on the motor type. Start windings can be twice that of the run. In the low ohms. Assuming single phase. Winding to winding should be in the Megaohms. Windings to ground in the mega to giga ohms. What do you have?
    I just checked from terminal to terminal, (well from wire to wire also before removing the wires) and I got near zero ohms. If I used the audible continuity setting it was zero, on ohms setting it was around 3 or 4 ohms. I figure I was reading through windings and switches so wasn't sure what I was actually reading.

    I know for sure it wasn't shorted. The call was for the 20A GFCI breaker tripping for all the equipment. I disconnected everything and connected them back one at a time. Breaker held until I put the pool pump back on so I knew it was the culprit. But wasn't sure if it had a ground fault or short. That's when I decided to measure the resistance.

    Since I wasn't sure of the readings, I decided to take out the GFCI breaker and replace it with a regular breaker just for a test. The motor ran on the regular breaker with no tripping. So I figured there was a ground fault somewhere in the motor. The back end of the motor where the terminals are was severely corroded. I advised the customer to have the pump motor replaced and I also put the GFCI breaker back in.

    Customer sent me a text saying replacing the pump motor fixed the tripping issue.
    If you aim at nothing, you will hit it every time!

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    3-4 sounds close enough for the windings without going into a lot of detail. Megging it would have shown your ground fault.
    Tom
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    Quote Originally Posted by ptonsparky View Post
    3-4 sounds close enough for the windings without going into a lot of detail. Megging it would have shown your ground fault.
    I forgot to mention that I also checked from terminals/wires to the motor housing. It was in mega ohms.
    I thought about megging the motor, but given the corrosion, I chose to just have them replace it.
    If you aim at nothing, you will hit it every time!

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    Quote Originally Posted by Little Bill View Post
    What should the reading be (just approximate) on a good pool pump motor when measuring resistance/ohms? The motor is 230V single phase. I don't know much about motor types so all I know is that it is for a pool pump. It is a US motor brand.
    I was going to say anything less than 10 ohms can probably be expected with no other information. Turn to turn short is hard to diagnose this way unless you know what resistance should be, because it isn't going to change that much with a turn to turn short. With three phase motors you at least should expect all windings to be the same but single phase motors main and aux winding may have different resistance so you can't necessarily compare them to one another.

    I had a spa pump one time that was tripping GFCI - problem was a leaking fitting was dripping onto motor. I cleaned it up and dried it out (and of course replaced leaky gasket in the fitting) and it was fine after that.
    I live for today, I'm just a day behind.

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    Quote Originally Posted by kwired View Post
    I was going to say anything less than 10 ohms can probably be expected with no other information. Turn to turn short is hard to diagnose this way unless you know what resistance should be, because it isn't going to change that much with a turn to turn short. With three phase motors you at least should expect all windings to be the same but single phase motors main and aux winding may have different resistance so you can't necessarily compare them to one another.

    I had a spa pump one time that was tripping GFCI - problem was a leaking fitting was dripping onto motor. I cleaned it up and dried it out (and of course replaced leaky gasket in the fitting) and it was fine after that.
    Along with age, this motor had been partially covered with water. Seems there was a leak in the plumbing and it flooded the area around the motor. HO said there was water up to over half way of the motor.
    If you aim at nothing, you will hit it every time!

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    Quote Originally Posted by Little Bill View Post
    Along with age, this motor had been partially covered with water. Seems there was a leak in the plumbing and it flooded the area around the motor. HO said there was water up to over half way of the motor.
    If you are accustomed to taking motors apart, it likely was able to be cleaned and dried and would have been fine.

    Centrifugal switches (stationary or moving parts) sometimes can be difficult to find if they are in bad shape and internal overload units can be harder to find also but most the rest of what is inside is easily cleaned up and ball bearings are relatively easy to replace if needed. Capacitors are usually easy to find if needed. Sleeve bearings aren't so easy to find replacements for, but ball bearings probably more common on this application. Not much else that can go wrong without damaging the motor winding itself.
    I live for today, I'm just a day behind.

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    Quote Originally Posted by kwired View Post
    If you are accustomed to taking motors apart, it likely was able to be cleaned and dried and would have been fine.

    Centrifugal switches (stationary or moving parts) sometimes can be difficult to find if they are in bad shape and internal overload units can be harder to find also but most the rest of what is inside is easily cleaned up and ball bearings are relatively easy to replace if needed. Capacitors are usually easy to find if needed. Sleeve bearings aren't so easy to find replacements for, but ball bearings probably more common on this application. Not much else that can go wrong without damaging the motor winding itself.
    I have taken them apart before, mostly for bearings. I took this service call on a "I'll squeeze you in" type thing. I really didn't have time. But the HO begged because they were having a pool party for their daughter's graduation. So I didn't even entertain the idea of taking anything apart. I just wanted to "git-er done", so I told them to have the pool store bring them another motor.
    If you aim at nothing, you will hit it every time!

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    Quote Originally Posted by Little Bill View Post
    I have taken them apart before, mostly for bearings. I took this service call on a "I'll squeeze you in" type thing. I really didn't have time. But the HO begged because they were having a pool party for their daughter's graduation. So I didn't even entertain the idea of taking anything apart. I just wanted to "git-er done", so I told them to have the pool store bring them another motor.
    There is no "pool store" anywhere nearby my neck of the woods, so I'd be trying to get the original to work first before giving in to a new replacement too easily.
    I live for today, I'm just a day behind.

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