Spark from Drain cleaner to Cast Iron main drain


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Old 10-16-17, 02:52 PM
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Spark from Drain cleaner to Cast Iron main drain

Not sure where to begin, I went to help my grand mother clear out her main drain. The main drain is located in the basement. The home is a bit old, as the main drain is cast iron. I plugged the auto feed drain cleaner I rented from home depot into a non-grounded GFCI outlet. As soon as the cable from the machine hit the cast iron cleanout, it arched. The GFCI outlet did not trip nor did the breaker.

Not knowing what to do, I thought for some reason the pipe has electricity (I’m not a professional), I turned off a few breakers from the panel including the power for the basement where the non-grounded GFCI i used is located. I tried again, after turning off a few breakers and plugged into an outlet that has a ground and the issue did not occur, no arch/spark.

Im assuming and could be completely off, but maybe the pipe does not have any electricity flowing. Im thinking the cast iron main drain is acting as a ground, when I plugged the rental drain cleaner into the non-grounded outlet, it treated the cast iron pipe as a ground? My grandmothers ground from the fuse box is connected maybe 5-6ft to a clamp that’s on a water pipe.

I will go back to perform more test. I have checked the machine I rented and its not defective. I would appreciate any advice or if anyone ran into this issue before. Thank you!
 
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Old 10-16-17, 03:10 PM
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Im thinking the cast iron main drain is acting as a ground, when I plugged the rental drain cleaner into the non-grounded outlet, it treated the cast iron pipe as a ground?
Yes that is what happened. But the question is raises is where did that stray voltage come from and why did it not trip the GFCI. It's possible the motor or cord on the rental machine was damaged and caused a small short. The GFCI still should have tripped. It's also possible the ungrounded circuit is wired incorrectly with the 3-prong GFCI receptacle. If there is a bootleg ground somewhere it might have caused this situation.
 
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Old 10-16-17, 03:17 PM
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Thank you for the reply! Just so I understand, you believe the GFCI outlet might be wired incorrectly?

Thinking way out there, due to something i read online. I believe the issue is the cast iron pipe acting as a ground but could the issue but a live wire touching the pipe or another wiring issue (neutral) somewhere else in the house? Right now,
 
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Old 10-16-17, 06:11 PM
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Also make sure that the current grounding clamp from the fuse box is in fact not interrupted and does connect to the drain line. If any pipe repair was done in the past, it's possible a PVC or ABS pipe may have been substituted after the grounding clamp.
 
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Old 10-17-17, 03:00 PM
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Thank you! I will check that as well. I know there is PEX lines under the faucet in the bathroom. I plan on posting the solution for others that might run into this situation.

Questions: I would love to duplicate the problem with the drain cleaner and cast iron main drain pipe but I want to avoid renting the machine again. Is there anyway I can test this issue without having to rent the machine again? I want to make sure the issue gets resolved.
 
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Old 10-17-17, 07:35 PM
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A simple VOM meter should tell you.
 
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Old 10-19-17, 11:32 AM
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Use your voltage meter to test with one probe on the cast iron and one probe in the receptacle slot(s). For example you should have around 120V between the hot slot and the iron pipe and very close to zero volts between the iron and the other two slots. You could also test some other circuits to other exposed metal surfaces in the house like copper plumbing or the range top to look for unusual readings. It's also a strong symptom if you every feel electric tingles in the shower or when using water like washing dishes. If the lights in the house get dimmer or brighter for no reason that's also an important clue.

There are a couple other situations that can cause a problem like this like a heating element in the water heater leaking current into the plumbing or sometimes a broken neutral wire in your electrical service entrance or the service entrance at a neighbor's house. Sometimes that stray current can travel along a city water system into a neighboring house.
 
 

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