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Old 11-19-2008, 02:49 AM   #1
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How to test pond pump motor for current leakage?


A pond pump went bad in the backyard, and kept tripping the gfi. I replaced the pump and everything is fine.

Is there any way to test the defective pond pump (just to learn, since I am done) to find out the cause of the problem, such as current leakage, etc?

A gfci needs about 4-6 milliamps to trip. My Fluke t5 doesn't go that small.

The pond pump only draws about .7 amps.

How can I test for the motor problem in milliamps or for current leakage? I hope I am asking the right questions since this is out of my field; I do residential electrical, not motor stuff...

Thanks

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Old 11-19-2008, 06:06 PM   #2
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How to test pond pump motor for current leakage?


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Originally Posted by Timster View Post
A pond pump went bad in the backyard, and kept tripping the gfi. I replaced the pump and everything is fine.

Is there any way to test the defective pond pump (just to learn, since I am done) to find out the cause of the problem, such as current leakage, etc?

A gfci needs about 4-6 milliamps to trip. My Fluke t5 doesn't go that small.

The pond pump only draws about .7 amps.

How can I test for the motor problem in milliamps or for current leakage? I hope I am asking the right questions since this is out of my field; I do residential electrical, not motor stuff...

Thanks
If your fish are behaving strangely, this could be a sign!

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Old 11-19-2008, 06:39 PM   #3
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How to test pond pump motor for current leakage?


No, there are no fish; the racoons ate them already. The GFCI is behaving strangely by tripping, and I already know it is the pond pump; the pond pump has been replaced and the problem is solved.

Thanks for trying.

Can anyone suggest a forum that may be able to answer this question?

Thanks guys.
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Old 11-19-2008, 07:52 PM   #4
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How to test pond pump motor for current leakage?


The only accurate way I know of is by the use of a meg-ohmmeter, commonly called a megger.

This instrument will apply a DC voltage, usually 250, 500, or 1000 volts to the power leads (in this case, the hot and neutral cord prongs), and it'll measure the current coming back up the ground (in this case, the ground cord prong). The test voltage is usually double the operating voltage.

This test is useful for finding defective equipment (that trips GFIs), and also to ensure a bit more safety before energizing a high current circuit. For example, if you turn on a 2000 amp breaker (common for me), and the wire insulation is skinned off somewhere in the conduit, the resulting explosion will very likely require a trip to the local ER......or maybe the morgue. A megger will ensure that the circuit is free from any faults.

The el-cheapo type (perfectly fine for this type of testing) will cost about $400 or so. They can likely be rented for alot less though.

Rob
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Old 11-19-2008, 08:34 PM   #5
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How to test pond pump motor for current leakage?


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The only accurate way I know of is by the use of a meg-ohmmeter, commonly called a megger.

This instrument will apply a DC voltage, usually 250, 500, or 1000 volts to the power leads (in this case, the hot and neutral cord prongs), and it'll measure the current coming back up the ground (in this case, the ground cord prong). The test voltage is usually double the operating voltage.

This test is useful for finding defective equipment (that trips GFIs), and also to ensure a bit more safety before energizing a high current circuit. For example, if you turn on a 2000 amp breaker (common for me), and the wire insulation is skinned off somewhere in the conduit, the resulting explosion will very likely require a trip to the local ER......or maybe the morgue. A megger will ensure that the circuit is free from any faults.

The el-cheapo type (perfectly fine for this type of testing) will cost about $400 or so. They can likely be rented for alot less though.

Rob
wow! A megger! I know that is usually used for large commercial applications like your 2000 amp stuff ; I had no idea, of course, that they would measure voltage differences so small.

I have spent more than that on other tools. I guess a fluke megger should be added to my collection now, or the el cheapo one...

I'll have to find uses for it in residential electrical problems, too, if possible. I will now research it. I know there are some megger threads on electriciantalk.com, so I will read them.

Thanks for the answer!
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Old 11-19-2008, 09:49 PM   #6
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How to test pond pump motor for current leakage?


Quote:
Originally Posted by Timster View Post
A pond pump went bad in the backyard, and kept tripping the gfi. I replaced the pump and everything is fine.

Is there any way to test the defective pond pump (just to learn, since I am done) to find out the cause of the problem, such as current leakage, etc?

A gfci needs about 4-6 milliamps to trip. My Fluke t5 doesn't go that small.

The pond pump only draws about .7 amps.

How can I test for the motor problem in milliamps or for current leakage? I hope I am asking the right questions since this is out of my field; I do residential electrical, not motor stuff...

Thanks
Start by looking for 30kohms or less between the motor hot lead and the motor shell with an ohmmeter.

If it's more than 30k you can check for voltage dependent leakage (maybe due to moisture) by putting 120v (through an isolation transformer if you have one) into the motor hot lead through a 10k, 2w resistor and ground the motor shell.
If there is 40v or more across the resistor, you've found the problem.
If no 40v then the problem may have been elsewhere.
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Old 11-19-2008, 11:09 PM   #7
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How to test pond pump motor for current leakage?


Wow, yoyozit that is going way over my head with that information... I guess this is the right forum for this question, ha ha

This is just a $40 water pump with a plastic watertight housing; I am just curious to find where/how it is tripping the gfi in my personal time.

If there is a tool that will help me do this, and assist in residential service calls, etc., it would be great. I am researching meggers right now. If there is something out there that can save me time, it would be great...

If there is a tool that could have told me whether the gfi is bad or not, instead of pulling the pump motor plug and waiting to see if the gfi trips again, carrying the plug to another gfi to see if it trips, opening up boxes and checking for moisture problems, checking for open neutrals, etc...

Any links to a potentially helpful diagnostic tool would be greatly appreciated.

I am doing more service calls lately than remodels probably due to economic conditions than others; but work is work.

I guess I am rambling...
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Old 11-20-2008, 08:38 AM   #8
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How to test pond pump motor for current leakage?


Quote:
Originally Posted by Timster View Post
If there is a tool that will help me do this, and assist in residential service calls, etc., it would be great. I am researching meggers right now. If there is something out there that can save me time, it would be great...

Any links to a potentially helpful diagnostic tool would be greatly appreciated.
Fluke makes a clamp-on meter for sensing differential current, just like a GFI does. Dunno' how long it will take to pay for itself.

A megger checks insulation resistance. With a GFI all you're interested in is whether the leakage current is more or less than ~4mA.

There is also reactive leakage current which a megger will not pick up because it applies DC to the thing you're testing.
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Old 11-23-2008, 09:54 PM   #9
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How to test pond pump motor for current leakage?


I would start with a standard ohm meter set at about 20K or so depending on what your meter has for settings. With the pump unplugged use the meter between the ground lug and the (power or return/neutral, doesn't matter too much if it is the power of return since internally of the motor they are connected in the windings). If the meter picks up a continuity (any reading but open) there is leakage and will most likely trip a good ground fault breaker. There are other ways the breaker can trip from a motor but I have found this to be the most common failer and easiest to test for.

PS just a note / Don't touch the metal part of the leads with your hands as this will be picked up on the meter and give a false bad reading on the motor.
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Old 11-24-2008, 10:44 PM   #10
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How to test pond pump motor for current leakage?


Thanks mopar and yoy.

Yeah, hindsight being 20/20, I guess it is not worth it to know 'exactly' how many milliamps caused a $40 water pump to fail; but at least I know it failed.

I bought a cheap multitester, and I like the idea mentioned of setting it on ohms at 20k. But this cheap $20 multitester is very frustrating since the numbers are flying all over the place.

Therefore, I am going to pick up a fluke multitester (around $200?) and then go from there, learning how to use it in smaller stuff.

I guess I really just need to know how to test 'good or bad' since there is no need to quantify the extent of good or bad in my work.

I don't know how anyone can use those $20 multitesters (but I know you guys can).

... Anyways, I am now going to take my grinder and grind away the plastic housing and look at the inside of the bad water pump, for fun.
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Old 11-24-2008, 10:51 PM   #11
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How to test pond pump motor for current leakage?


If the number are all over the place. Perhaps your fingers are touching the lead ends?? It will read body resistance as well as slight current from you body and freak out the meter. Also some meters have to be zeroed. Touch the leads together (zero ohms) and then you would push a zero cal button if equipped so it will reference the resistance correctly
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Old 11-25-2008, 12:56 AM   #12
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How to test pond pump motor for current leakage?


Thanks Mopar.

I have done everything right with this multitester, and perhaps I may have gotten a bad one; it won't even register the plugged in pump at 120 volts on the 200v setting (did I do that wrong?), while my Fluke T5 hits a stable 120v (actually the broken pump hits a stable 121v on a non-GFCI circuit)... but the cheap multitester registers no volts, however...

Probably shouldn't have picked up such a cheap multimeter from the local hardware store, I guess, but my friend that fixes appliances for a living, swears by his, but he has a different model, and he says his is way better (after I bought mine)...

On a side note, my friend (appliance guy) says he has never been busier, since everybody wants to fix their appliances now, rather than buy another new one; I guess he has a recession proof business model.

But I digress... I thought all cheap multitesters were the same; I was wrong, so I am going to go with a Fluke, and start learning.

Thanks again guys.
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Old 11-25-2008, 03:26 PM   #13
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How to test pond pump motor for current leakage?


If it's good it's a Fluke!

Almost any working multimeter will do what you need, even one that has a sensitivity of 1000Ω/volt.

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