Resistance Check on a Pool pump Motor

[Little Bill]

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.

 

[ptonsparky]

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?

 

[Little Bill]

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.

 

[ptonsparky]

3-4 sounds close enough for the windings without going into a lot of detail. Megging it would have shown your ground fault.

 

[Little Bill]

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.

 

[kwired]

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.

 

[Little Bill]

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.

 

[kwired]

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.

 

[Little Bill]

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.

 

[kwired]

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.

 

[Mystic Pools]

We don't repair motors anymore, in fact for years. We don't even replace residential backyard motors either. We replace the entire pump which gives the homeowner a new warranty.

Once the bearings go on motors, it usually damages the bearing race the shaft rides on. Even if that's all good and you can replace the bearings, a new motor shaft is needed, possibly a new impeller, volute-now the cost is going up for the repair. By that point your more than halfway to a new pump.

The pump manufacturers have gotten smart over the last few years and they know their competition. They design replacement pumps to match up to existing plumbing of the competitors for an easy swap. Little downtime for a homeowner especially when parties are in the works.

The commercial motors I have worked on in the past, are sometimes worth repairing. 5-15 HP pumps can be $6K-$10K

 

[kwired]

We don't repair motors anymore, in fact for years. We don't even replace residential backyard motors either. We replace the entire pump which gives the homeowner a new warranty.

Once the bearings go on motors, it usually damages the bearing race the shaft rides on. Even if that's all good and you can replace the bearings, a new motor shaft is needed, possibly a new impeller, volute-now the cost is going up for the repair. By that point your more than halfway to a new pump.

The pump manufacturers have gotten smart over the last few years and they know their competition. They design replacement pumps to match up to existing plumbing of the competitors for an easy swap. Little downtime for a homeowner especially when parties are in the works.

The commercial motors I have worked on in the past, are sometimes worth repairing. 5-15 HP pumps can be $6K-$10K

For a pool guy in a metro area, makes sense. No pools guys within 100 or even 150 miles from me, closest thing is spa dealers that also do some above ground pools. Service calls to drive 100 miles makes the complete pump cost seem like nothing I imagine.

I don't fully get what you mean with bearing race being damaged. I replace a lot of ball bearings in various motors, wearing of end housings where the outer portion of bearing sits is the biggest thing that wears out besides the bearing itself, motor shafts are almost always fine. If you are talking about a sleeve type bearing then the shaft can be an issue sometimes, but the sleeve is the softer material and is usually what wears the most. I don't think motors with that kind of bearing are typically used on this kind of equipment though, mostly limited to blower motors up to about 1 HP or other motors under 1/6 HP.