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Old 04-18-2012, 11:01 AM   #1
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Grounding steel drain pipe


In a 1950s home the electrical is being redone. Wallboard was removed in the kitchen and there is a kitchen sink drain/vent line (seems to be 1" to 1-1/2" pipe) in the wall which is made of steel. It runs down into the concrete slab and up through the roof. There is an old electrical outlet (which will be removed and replaced) next to it which has a 14/2 cable and a separate small ground conductor running to it. With a meter I measure 50V between the steel pipe and the steel housing of the receptacle. Once the old receptacle is removed and a new one is installed, where and how will the drain pipe be grounded? I am sure there are more steel drain pipes used in this house but not all of them are open and exposed. Will it be sufficient to ground this one steel drain/vent line? If yes how and with what conductor size?

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Old 04-18-2012, 11:05 AM   #2
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Grounding steel drain pipe


If it is in the slab, it is already grounded. Disregard what you saw on the meter. Rookie mistake.

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Old 04-18-2012, 11:17 AM   #3
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Grounding steel drain pipe


Anytime a wall is open and that old steel pipe is exposed it's best to take the time to replace it.
At some point it is going to fail and your going to be stuck having to rip out a whole bunch of stuff to get at it.
As soon as I moved into the house I own the old steel drain line collaped, the steel supply line but out rusty water and were almost totaly plugged up on the inside and had leaked where it ran into the slab.
Replaced all if it with Pex and PVC, no more rust, way better flow, and the drains run faster.
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Old 04-18-2012, 11:53 AM   #4
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Grounding steel drain pipe


The reason why I even measured it was because I felt little shocks when I grabbed the steel pipe while lugging a cord into the outlet and my hand touched the steel box of the outlet. This shouldn't be the case, right?
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Old 04-18-2012, 01:13 PM   #5
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Grounding steel drain pipe


That is because you were plugging something in, then grabbing a hold of something that was not at the same potential. Basically your body became the path to ground, due to the outlet was not properly grounded to begin with. I would be checking back at the panel to make sure that it is correctly installed, then start checking the other outlets to see if they were jury rigged like the one outlet you were messing with, and correct them.
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Old 04-18-2012, 04:00 PM   #6
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Grounding steel drain pipe


I guess this is my point. The steel pipe should have the same potential as the box of the outlet. Even without plugging something in I can feel the 50V difference between the two steel parts. A new main and sub panel is being put in. How should the drain be grounded now.

Someone mentioned to take it out and replace it. I can only get to a certain portion f it though. The part that continues up through the roof I can't remove. So there would still be steel pipe left that I assume will need to be grounded.

I understand that steel drain lines are usually centrally grounded but only the piece in the wall is currently exposed. The old main panel and the box the cable runs to looks fine. No ground fault there.
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Old 04-18-2012, 04:07 PM   #7
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Grounding steel drain pipe


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Originally Posted by Jaxx View Post
I guess this is my point. The steel pipe should have the same potential as the box of the outlet. Even without plugging something in I can feel the 50V difference between the two steel parts. A new main and sub panel is being put in. How should the drain be grounded now.

Someone mentioned to take it out and replace it. I can only get to a certain portion f it though. The part that continues up through the roof I can't remove. So there would still be steel pipe left that I assume will need to be grounded.

I understand that steel drain lines are usually centrally grounded but only the piece in the wall is currently exposed. The old main panel and the box the cable runs to looks fine. No ground fault there.
Your "understanding" that steel(cast iron?) drain pipes are usually grounded is news to me.
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Old 04-18-2012, 06:24 PM   #8
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Grounding steel drain pipe


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Originally Posted by brric
Your "understanding" that steel(cast iron?) drain pipes are usually grounded is news to me.
They are, when they are in contact with Earth. Otherwise if in a slab and no contact, I would think then that you would have to use a Ufer.
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Old 04-19-2012, 01:17 AM   #9
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They are, when they are in contact with Earth. Otherwise if in a slab and no contact, I would think then that you would have to use a Ufer.
A ufer is probably nothing that can be used in this case because the slab is all done, correct?

Measured from the same steel outlet box to the main cold water line there are also over 40V difference. 0 difference between the cold water line and the drain/vent line.

Doesn't this seem like the water and drain system are not grounded (connected to the electrical system ground) anywhere, keeping in mind this is a 1950s house?
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Old 04-19-2012, 08:16 AM   #10
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A ufer is probably nothing that can be used in this case because the slab is all done, correct?

Measured from the same steel outlet box to the main cold water line there are also over 40V difference. 0 difference between the cold water line and the drain/vent line.

Doesn't this seem like the water and drain system are not grounded (connected to the electrical system ground) anywhere, keeping in mind this is a 1950s house?
No, means that your meter is stating "Phantom" Voltage. Put a 40w light bulb on the circuit to load it, and bet that 40-50 volts will disappear.
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Old 04-19-2012, 11:35 AM   #11
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Grounding steel drain pipe


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Originally Posted by Jaxx View Post
The reason why I even measured it was because I felt little shocks when I grabbed the steel pipe while lugging a cord into the outlet and my hand touched the steel box of the outlet. This shouldn't be the case, right?
this should definitely not be the case. unless the insulation on the cord was damaged or something, no one should be feeling any shocks when grabbing metal pipe. just because the pipe is touching the concrete doesn't mean it has a good ground. pipe could be coated, outside could have rusted, etc. this decreases the effectiveness of the ground connection.

all the metal pipe should be bonded. you may need to add a bonding clamp to the pipe and run a bonding jumper to an effectively grounded component.
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Old 04-19-2012, 07:05 PM   #12
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Grounding steel drain pipe


You need to find out whether either the steel outlet box or the drain pipe was energized as opposed to not grounded. If one was neither grounded nor energized then touching it would not give you a shock.

If the outlet box was not adequately grounded, phantom voltage could play a role and would count towards energizing the outlet box while the drain pipe may well have already been adequately grounded.
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Old 04-19-2012, 09:24 PM   #13
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Grounding steel drain pipe


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all the metal pipe should be bonded. you may need to add a bonding clamp to the pipe and run a bonding jumper to an effectively grounded component.
Are you saying that DWV plumbing should be bonded to earth?

I think the whole problem is this 1950's house had a three prong receptacle added and it was improperly "grounded" with a wire to a drain pipe.
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Old 04-19-2012, 10:39 PM   #14
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Grounding steel drain pipe


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all the metal pipe should be bonded. you may need to add a bonding clamp to the pipe and run a bonding jumper to an effectively grounded component.
Where would I run the bonding jumper to? To the new electrical box using 12 gauge wire? It's a kitchen small appliance circuit. Or would it need to be run to the sub or even main panel?
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Old 04-19-2012, 11:04 PM   #15
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Grounding steel drain pipe


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Are you saying that DWV plumbing should be bonded to earth?

I think the whole problem is this 1950's house had a three prong receptacle added and it was improperly "grounded" with a wire to a drain pipe.
to answer your question, sort of. like a million other things in the code, there is a catch. 'other metal piping' that is 'likely to be energized' needs to be bonded. obviously open to interpretation. i'm more a fan of the informal note associated with the code section which states 'bonding all piping and metal air duct within the premises will provide additional safety'.

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