Thermally Protected 1 HP Well Pump

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powerplay

Senior Member
I have ran across an 1 HP Well Pump that is supposed to read 2.1-3.1 ohms across 2 wire line leads normally, but have read 3.6 ohms. I can imagine a lower resistive reading as being compromised insulation within the winding, but a higher value would be a corroded connection inside the well?

When the water hose was kinked, and no water is flowing through, would the pump motor temporarily hard wired have gotten hot enough to burnt out the motor?...or would the thermal protection have tripped and protected the motor protected the motor? Apparently the "thermal protection" is a kind of a clutch/ratchet that disengages when too hot.

Thanks again!
 

powerplay

Senior Member
For temporary measures, an motor controller wasn't used and the installer had connected the Well Pump to 240 volt line voltage with an dryer plug and receptacle which was plugged in when water was needed. There was no control box, but the motor was "thermally protected", and I was wondering if that would protect against motor burning out from an kinked hose?
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
If the motor nameplate or data sheet definitely says "Thermally Protected" on it, that means it has a Klixon thermal cutout embedded in the stator windings in series with the circuit feeding power to them. When the windings themselves reach a specific temperature, far below the thermal damage curve of the insulation, the Kilxon snaps open and cuts power to the motor. When it cools down, it snaps back and the motor re-starts if the control circuit allows it to, which is the case most of the time because there is no direct interface of the Klixon to the controls. If your motor has this feature, you do NOT need another external OL relay. So to answer that part of your question, YES, the motor would have protected itself.

Secondly, if it is a centrifugal pump of any kind (as most water well pumps are), kinking the hose would NOT have caused it to overheat, in fact it would have UNLOADED the motor. Load on a centrifugal pump is directly related to flow. No flow, no load.

Lastly if you were in fact using a standard VOM to look at winding resistance, I agree with ptonspary with regards to the meter readings; almost totally meaningless. About the only value in taking a standard VOM meter to an AC motor winding is to tell you if it is completely open or completely shorted, and even the completely shorted is difficult to tell. For anything else you need a Megohmeter, or better known as a Megger, which charges up to hundreds of volts to determine if the insulation is compromised. So when the data sheet for your pump said 2.1 - 3.1 ohms, there were providing that info for a motor shop who would be testing it at 300VDC (for a 240V motor), not 9VDC from the little battery in your VOM. If you have a concern for the seals etc., you can rent a Megger in many areas, but you may need help in learning to use it properly if you've never done it. If you did take those measurements with a Megger, then your theory on a corroded connection may be possible. But it could also just be a manufacturing issue as well. When they give resistance values, it's typically for the purpose of establishing MINIMUM resistance, not maximum.

(I had to look up what a "dutch ratchet" was, Google seems to think the only possibility is a supplier of mechanic's tools in the Netherlands ;) )
 
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kwired

Electron manager
Location
NE Nebraska
Were you reading resistance of the windings at the pump motor or through the extension leads running down the well casing. They will add resistance to your measurement. Some places this can be 2-300 feet or even more of conductor.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
If there is a thermal device in the windings you are much better off, they usually fail to the safe side. A klixon that is typically mounted in the pecker head or the control box will care less how hot the motor is. Submersible require a minimum amount of water flow to cool them. Blocked discharge can and has melted the plastic drop pipe allowing the pump to drop even further. Fun stuff from what I understand.
 

powerplay

Senior Member
If the rubber water hose had being kinked on several occassions preventing water flow, am i clear in understanding that the Klixon would prevent damage as in this Grundfos 1 HP thermally protected motor if in the stator windings? ...or not sensitive enough to protect the motor if no water was flowing past in this case and the power was turned on more than once?
 

gndrod

Senior Member
Location
Ca and Wa
Model?

Model?

I have ran across an 1 HP Well Pump that is supposed to read 2.1-3.1 ohms across 2 wire line leads normally, but have read 3.6 ohms. I can imagine a lower resistive reading as being compromised insulation within the winding, but a higher value would be a corroded connection inside the well?

When the water hose was kinked, and no water is flowing through, would the pump motor temporarily hard wired have gotten hot enough to burnt out the motor?...or would the thermal protection have tripped and protected the motor protected the motor? Apparently the "thermal protection" is a kind of a clutch/ratchet that disengages when too hot.

Thanks again!

The Grundfos model type was not mentioned. (SQN,SQE, MS3 MSE 3....etc) There are temperature, flow rate control wiring in different models from Grundfos with metric conversion adaption needed. The submersible permanent magnet pumps are not capable of being deep well tested as far as I know.
 
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