Motor Ground Faults & Testing

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lifefloat

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First post here, and not a big social media user but I have an issue that I'd like some good feedback on from the electrical community at large.

Here's the specs:

Single phase motor. 1 HP. Dual voltage 120/240. Motor running at 240V.

Here's the installation:

Boat lift. Typically two motors controlled by a manufactured controller containing contactors to shift motor direction.

Controller does not require a neutral.


Here's the issue:

After a year or two some of these installations are developing ground faults at the motors. GFCI circuit breaker does it's job and opens. I'm not sure why the lifetime is so brief for some of these motors. Is is abuse to the motor and possible insulation is lost on the motor windings resulting in a case ground fault? Is is environmental factors like moisture or debris in the motor? Lack of use and the motor develops internal corrosion issues? Cheap motors? Owners applying corrosion block to external case? These all seem like probable reasons for potential ground faults but tough to verify unless totally obvious issues exist.

It is impractical to disassemble a small motor like this in the field to look for gremlins. Overall the motors are pretty well protected the way they are installed in the application. At the risk of answering my own question, can we probably attribute this issue to mis-use of the motor causing premature failure?

BTW if the GFCI protection is removed 99.9% of the time the motor(s) run completely in spec.

Any suggestions for general testing guidelines?

Thanks to anyone who has any helpful insight or feedback to this matter.
 
Is is abuse to the motor and possible insulation is lost on the motor windings resulting in a case ground fault? Is is environmental factors like moisture or debris in the motor? Lack of use and the motor develops internal corrosion issues? Cheap motors? Owners applying corrosion block to external case?
Most likely all or some of the above. Looks like you are caught between a rock and a hard place. Even though the controller has no neutral, I would bet that the GF occurs because the 240V source xfmr has a ground reference. Plus the GFCI device is a people protector and designed with a very low current pickup point (5 MA?) and can trip if you look at it the wrong way :angel:
Maybe a redesign of the circuit using an isolation xfmr may help but without knowing the circuit and what the code regulations require with regard to personnel safety (shock prevention) one hesitates to make any recommendations. I would be curious to know what the meg-ohms reading would be if you took a 500V megger and measured between the motor winding and ground on a tripping circuit vs a good one.
I am sure this problem is not unique and there are solutions out there. Maybe someone with more experience in this area can chime in.
 
lifefloat said:
BTW if the GFCI protection is removed 99.9% of the time the motor(s) run completely in spec.
Click to expand...

This is pretty much immaterial to your situation. It can lead you to chase things that aren't a problem while ignoring the real issue, current is flowing where it shouldn't be.

A standard protective device is looking for line current greater than it should. For the most part a GF device is looking for line current lower than it should be.
A standard GF device does not ever measure current on the ground wire. The typical GF device compares the current leaving the breaker versus what comes back into it. If the difference is great enough the GF device figures the current is flowing on an unintended path.
 
jim dungar said:
This is pretty much immaterial to your situation. It can lead you to chase things that aren't a problem while ignoring the real issue, current is flowing where it shouldn't be.

A standard protective device is looking for line current greater than it should. For the most part a GF device is looking for line current lower than it should be.
A standard GF device does not ever measure current on the ground wire. The typical GF device compares the current leaving the breaker versus what comes back into it. If the difference is great enough the GF device figures the current is flowing on an unintended path.
Click to expand...

So are you stating that the ground wire or earth is not the unintended path?
 
I'm not sure if a boat lift requires a personnel type GFCI or not, probably does. If so, one issue may be the exposure to the elements and the fact they are likely seldom used. This ends up creating a situation where the motor gets warm when used, then cools off and moisture condenses on it, then just sits there for a while. Eventually it infiltrates through insulation and seals and gets to where a GFCI will see the leakage.

The way to prevent it is to have motor heaters keeping everything warm all of the time. But users tend to not like seeing the power bill for that. Even though it's typically low power, it's constant. So it's a trick to get the user to weigh the benefits against the costs.
 
Boat lift GFI

Boat lift GFI

What brand motors are you using, are they sealed or open on the ends. If you are using sealed motors make sure the capacitor cover seals are intact and pointing up when possible. The sealed motors have 4 drip holes with rubber plugs in the case, when installed the hole on the bottom should be opened. I hope this helps
 
ATSman said:
So are you stating that the ground wire or earth is not the unintended path?
Click to expand...
Are you suggesting they are intended?

There could be exceptions, but for circuits built to the NEC, current flowing out of a protective device is intended to be returned via another conductor of its circuit, not via a ground wire or earth.
Except for some protective devices that measure current on ground paths (e.g. HRG systems), GF devices primarly function on the concept of 'what goes out the sensor, must come back through the sensor'.
 
Just as a guess, I would suspect some kind of corrosion due to humidity, and maybe salt if it is on the ocean.

The only real solution is likely to be a motor that is designed to take this kind of abuse.

ETA: There are some products that are called vapor phase corrosion inhibitors that might help. maybe put some in the motor junction box.
 
jim dungar said:
Are you suggesting they are intended?

There could be exceptions, but for circuits built to the NEC, current flowing out of a protective device is intended to be returned via another conductor of its circuit, not via a ground wire or earth.
Except for some protective devices that measure current on ground paths (e.g. HRG systems), GF devices primarly function on the concept of 'what goes out the sensor, must come back through the sensor'.
Click to expand...

Jim, the one important fact that you are overlooking is if this is a grounded system per the NEC (neutral grounded) then the only other path back to the source during the fault has to be thru a ground path (wire or earth.)
 
ATSman said:
Is is abuse to the motor and possible insulation is lost on the motor windings resulting in a case ground fault? Is is environmental factors like moisture or debris in the motor? Lack of use and the motor develops internal corrosion issues? Cheap motors? Owners applying corrosion block to external case?
Most likely all or some of the above. Looks like you are caught between a rock and a hard place. Even though the controller has no neutral, I would bet that the GF occurs because the 240V source xfmr has a ground reference. Plus the GFCI device is a people protector and designed with a very low current pickup point (5 MA?) and can trip if you look at it the wrong way :angel:
Maybe a redesign of the circuit using an isolation xfmr may help but without knowing the circuit and what the code regulations require with regard to personnel safety (shock prevention) one hesitates to make any recommendations. I would be curious to know what the meg-ohms reading would be if you took a 500V megger and measured between the motor winding and ground on a tripping circuit vs a good one.
I am sure this problem is not unique and there are solutions out there. Maybe someone with more experience in this area can chime in.
Click to expand...

I am stuck between a rock and a hard place here. Thanks for seeing that.

The x former is grounded. The motors are grounded. The whole thing is grounded. The fault is occurring at the motor specifically and is it likely environmental conditions that are causing the GFCI circuit breaker to see a slight imbalance on the current flow.
 
jim dungar said:
This is pretty much immaterial to your situation. It can lead you to chase things that aren't a problem while ignoring the real issue, current is flowing where it shouldn't be.

A standard protective device is looking for line current greater than it should. For the most part a GF device is looking for line current lower than it should be.
A standard GF device does not ever measure current on the ground wire. The typical GF device compares the current leaving the breaker versus what comes back into it. If the difference is great enough the GF device figures the current is flowing on an unintended path.
Click to expand...


Agree totally.
 
Rlytle said:
What brand motors are you using, are they sealed or open on the ends. If you are using sealed motors make sure the capacitor cover seals are intact and pointing up when possible. The sealed motors have 4 drip holes with rubber plugs in the case, when installed the hole on the bottom should be opened. I hope this helps
Click to expand...

Motors are typically AO Smith sealed motors. And yes they do have the rubber drip plugs on the case. Additionally the cap is pretty much positioned top facing. But those cap seals could be an entry point for moisture or debris I agree 100%. I will inform the mechanical installers of the equipment of the importance of the rubber seals on the case and pay better attention to those myself.

Thanks
 
petersonra said:
Just as a guess, I would suspect some kind of corrosion due to humidity, and maybe salt if it is on the ocean.

The only real solution is likely to be a motor that is designed to take this kind of abuse.

ETA: There are some products that are called vapor phase corrosion inhibitors that might help. maybe put some in the motor junction box.
Click to expand...

These installations are here in Florida where the humidity is out of control. And they are all exposed to salt air. Pretty much the worst place you can put an electric motor. A big thanks goes out to the NEC for making GFCI protection a requirement on these installations in 2005. I understand the reason it made it into the code cycle and stuck but it makes my life hell that a totally sound installation potentially becomes and issue due to a grain of salt inside the motor winding.
 
Thanks to all that have replied to my dilemma concerning the motor ground faults.

I looks like the best solution is to mitigate any possible environmental contamination to the motors and hope that the end user understands the same.

Wash down rated motors may be a solution, or a redesign by the mechanical contractor to protect the motors currently in use.

Another thing that may bear some relief to my issue is discarding the GFCI protection altogether. Not sure if I can sell that one to an inspector but consider the following:

NEC Article 210.8 (C) states GFCI protection for outlets not exceeding 240V. This is pretty clear.

If you look at the NEC Handbook at this same article though, the editor's note mentions "GFCI protection for must be provided for boat hoists supplied by 15-or 20-ampere branch circuits rated 240V or less".

What if you fused it at 30-ampere based on Table 430.22(E) Duty-Cycle Service. Continuous rated motor, varying duty at 200% of motor nameplate.

Two motors 6.1 A each @ 240V.

Article 430.55 Combined Overcurrent Protection allows for one single protective device for this application provided it is a time inverse fuse.

Or am I grasping at straws here?
 
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