Electrical Sparks while drain cleaning????

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  #1  
Old 01-19-06, 01:58 PM
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Electrical Sparks while drain cleaning????

How did this happen?

Customer called this morning for a clogged kitchen sink drain. The piping was copper with a brass cleanout tee.

My drain cleaning machine *had* a GFCI end on it but it broke, I've been taking my chances with it ever since. I always wear gloves, rubber and thank goodness I had them on before what happened.

As soon as my cable hit the cleanout, it arched like you would of taken two 110 legs and connected them. The arc was super bright and I'm sure I could of fused my cable to the drain. It left burn marks on the cable where it touched.

Since this is the first time this has ever happened, I went to the truck and grabbed my $45 GFCI 3ft. cord. Plug it in, same result!!! How in the world was the drain cleaning machine working as a conductor of electricity through a GFCI? Nothing was wet, nothing is wrong with the machine. It's a small Spartan 81 where the drum is belt driven, not connected directly to the motor.

Totally amazed by what happened, I explained to the customer that possibly the outlet I connected to is wrong or there is a wire making contact with the copper stack heading to the second floor somewhere.....?

I ended up taking the GFCI 3ft cord and hooking my machine into the outlet that serves the washing machine and no problems after that. I also used the machine on the next job, different location like the 100's of times I've done before without electrical sparks involved.

I want to know how this could even happen when the machine *should* NOT be a conductor of electricity, whether a GFCI connected or not. I almost believe 100% that it is not my equipment, but something wrong with what I plugged into or the piping I was working on.

If you have any theory on this, I would appreciate some knowledge on this matter and if I need to have this customer call an electrician immediately to avoid electrocution.


Here is an image of the machine that was used.

 
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  #2  
Old 01-19-06, 02:07 PM
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It only happened in the ONE receptacle at that one location, right? Perhaps the grounding slot was connected to the hot wire at that receptacle? With your GFCI monitoring the hot/neutral, it would still pass the "ground" right around it. Does your machine have a 3-prong plug with ground? Was that receptacle already being used for other things by the homeowner?
 
  #3  
Old 01-20-06, 06:33 PM
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sorry for long post

I'm neither a plumber nor an electrician, BUT I had a similar situation. A halogen work light I was using while repairing a broken cast iron closet flange tipped and the metal guard arced continuously against the flange. I had to kick it away with my boot. There were small melt marks in the cast iron!!! This was slab construction, so the waste pipe was in the ground.

Light was plugged into a non-grounded GFCI receptacle. GFCI didn't trip. It's just looking for an alternate current path to ground other than the neutral. So where did this current come from?

Inspection and testing of the light and GFCI indicated that all was as expected. GFCI was wired correctly and tested correctly. Light equipment ground/case/guard were isolated from neutral and hot, neutral isolated from hot. No shorts in light cable or heavy duty extension cord.

BUT with the light plugged in, I was able to measure 120V between the metal guard and the cast iron pipe with a multimeter. No, folks, I didn't use my neon tester - but phantom voltage doesn't arc. I tried the same test using a different (non-grounded) GFCI receptacle on a different circuit. Same result.

Now I would expect a non-grounded conductive surface - such as the metal guard on the light to be at some voltage potential other than 0V. And then there's the matter of induced voltage. But are these enough to cause sustained arcing? I don't think so. Having recently received mild shocks off and on from other equipment using three prong plugs into a non-grounded GFCI - I stopped using tools that required an equipment ground all together until I could get to the service upgrade.

A month or so later, when I was doing the service upgrade, I found a possible cause. The service entrance single grounding electrode was the 50 year old badly rusted steel water pipe. The house had been repiped with pvc and the old pipe had been disconnected from the water meter about 40 feet away. The old pipe was not bonded to the water meter. All of the under slab steel pipe was still there - just bypassed. The actual grounding electrode conductor connection was underground (about 12") and was just a mass of rust. Just for kicks, I installed one of the new ground rods, and measured about 80V between the new rod and the existing grounding electrode conductor (main breaker off). I did use my neon tester this time, but it didn't light - but if I recall correctly, they don't fire until 90V or so... I connected a wire to the new ground rod and (very carefully) touched the wire to the existing grounding electrode conductor. I got an arc! Current/voltage check showed about 300ma @ about 50V RMS from existing grounding electrode conductor to new ground rod. Yikes!!!! The pro's here are probably laughing themselves silly, but I'll go on...

It appears that the whole service was floating with respect to "true" ground - the ground we walk on. I'm thinking that there was also an issue with the service neutral, because I can't imagine that the PoCo ground would be that far away. And I still don't completely understand the arcing. Anyway, when I replaced the service, the problem went away. Before I rewired the house, (and installed the new toilet) I tried the light vs closet flange test again (same light, same ungrounded GFCI just new service). Yes, I was a bit unnerved by it all... I still measured about 120V between the guard and the closet flange with my multimeter. This is simply a difference in potential and/or induced voltage - true phantom voltage - and I was not able to get it to arc again....

Lessons learned:

1. The equipment ground is there for a reason. If something has a grounding plug - it needs to be grounded.

2. Just because there is a ground, doesn't mean the ground is good.

3. There are some things in life I'll never truly figure out.

My (totally non-professional) theory in your case? Same as in mine. You didn't mention if the breaker tripped, so I'll assume that it didn't (If it did - that's a very different and very dangerous problem). I'm also going to assume that the first receptacle you used did not provide an appropriate equipment ground - but I can't imagine that your machine doesn't require one. Mac asked about this also. Maybe the second one didn't either? But served well anyway?

My theory is that there was a significant difference in electrical potential between your machine and the pipe. That is - the ground references were different. The primary reason for equipment grounds is to guard against that. Yes, they also help protect against internal failure, but an equipment ground is designed to maintain exposed conductive surfaces at 0V potential with respect to the primary electrical ground. Even if you were plugged in to a non-grounded receptacle using a "cheater" adapter or GFCI - that in itself does not completely explain the arcing you experienced. In short, the pipe you were working on wasn't electrically bonded to your machine. There's several ways that can happen - beyond cheater adaptors and age.

The most important part of my theory is that what you experienced implies that there may be an electrical problem somewhere that should be addressed. Someone could get hurt (or worse) eventually, unless it's identified and resolved. My advice - have your machine checked out. And if it checks out ok - call the homeowner and express your concerns. At the very least, you'll sleep better... ;-)
 

Last edited by rodek01; 01-20-06 at 06:42 PM. Reason: correct wording re pipe bonding
  #4  
Old 01-21-06, 08:08 AM
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Shocking plumbing situations

There is a requirement for the water lines to be bonded to the service. If you lose the neutral conductor then the water lines become a neutral. When something is disconnected or in this case connected by the contact, it will try to carry the load through your equipment. A plumber friend of mine was killed by such a situation. Next time, before you start, get your meter out and see if there is voltage from your equipment to what you are working on. You would be surprised. Neutrals + grounds can kill too!
 
  #5  
Old 01-21-06, 01:21 PM
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I wonder if that receptacle was a two prong at one point and some illegally bonded the ground to the neutral.
 
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