grounding question

OK, i did my homework on this one, but still have some questions

I understand the NEC code for grouding:

"A metal underground water pipe in direct contact with the earth for 10 feet or more (including any metal well casing effectively bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joints or sections or insulating pipe) to the points of connection of the grounding electrode conductor and the bonding conductors."

My question is as follows: Is there any problem with grounding TWO separate outlets to the SAME galvanized water supply pipe?

Basically, I have a lot of Knob and Tube wiring in my place. I'm grounding some existing outlets by pigtailing a ground wire to the metal box, and running a ground wire to my galvanized water supply pipe. I know that the supply lines are all galvanized, and underground, so i am sure that this meets the NEC code above.

Finally, does the bug-eye tester check for an actual ground, or does it just make sure the wires are in the right spots? (i.e., will it read as 'open ground' if i run a ground wire, but that ground wire doesnt run to the ground?

 

The proper way to run a ground is to run it to the ground bar in the panel. If you are ging to run a ground wire why not just run new nmb cable and have the circuit off the old K&T.

 

i didnt want to fish new NM... question remains, does my grounding method provide any additional safety at all?

also, what about the bug eye tester?

 

If its temporary, just use a gfi. IMO its not ok to simply run a ground wire from the nearest water pipe to use as an equipment ground.
i base this opinion on 250-130 (C)(1), It refers you to 250-50. If you read 250-52(A)(1) it says "........Interior metal water piping located more than 5' from the point of entrance to the building shall not be used as part of the grounding electrode system.........."
So my opinion is; you cant use the water pipes to ground a non-grounded branch circuit unless you run the wire to within 5' of the entrance.
If the case is that your running them all the way back to within 5', I dont see a problem with it.

 

Guevara,

I know that you are going to find this quite hard to believe, but your method of grounding not only provides no additional safety, it provides significant additional danger. No grounding at all is safer than what you have done!!

You have made a fundamental and dangerous misinterpretation of the NEC. You quoted an article that applies to the grounding electrode system, and then applied it to the equipment grounding system. These two systems operate on two completely different set of principles, serve two completely different purposes, and are covered by two completely different set of codes.

No, do not use the plumbing for the equipment grounding system. Yes, use the plumbing for the grounding electrode system.

Note: The panel grounding bar is part of both systems. And code does allow you to use the first five feet of the plumbing to ground equipment, but only if that five feet is also connected to the panel with a grounding electrode conductor. Essentially, by connecting the equipment grounding conductors to this section of pipe, you are indirectly connecting it to the grounding bar in the panel via the wire from there to the panel. This confines the dangerous condition to just these five feet of pipe, a hazard the NEC finds acceptible.

 

Is that directed towards me or Guevara?

 

It's directed toward the person it's addressed to.

 

John:
I've been in the business for 26 years and am asking for clarification where you suggest to Guevara that there is "significant additional danger" from using the H2O as a grounding means within the residence.

I understand your intrepretation of the code but I do not understand what this "significant danger" would be. If there is
a fault current present within the first 5' of the water line, that
fault current would be present throughout the H2O system.

I would suggest that grounding to the H2O system anywhere, is
better than no ground at all.

Thanks,
SF_Elect.

 

I don't think so. Current doesn't wander around. It only heads for lower potential. And it isn't going to find that by wandering around the house.

There are multiple problems with using random spots on the plumbing as ground.

• First and foremost is the fact that the pipe does not have zero resistance. So a few tens of thousands of amps of fault curent flowing through the plumbing is enough to raise the voltage of the kitchen faucet to dangerous levels, even though the pipe has very low resistance, and even though the breaker will trip pretty soon (but not soon enough).
• Second is incredible risk created if the plumbing is not actually connected to the panel ground. In this case, a fault can raise the voltage of the pipe to darn near 120 volts (since the earth is a pretty poor conductor). At least if you connect an EGC near the GEC, you can see whether or not this hazard exists.
• Third is the hazard created if somebody replaces (or has already replaced) a section of that metal pipe anywhere with PVC or PEX. In this case, that kitchen faucet will definitely go to the full 120 volts in the event of a fault.
• Fourth is the risk to the next plumber (or homeowner) who is working on the plumbing, once he cuts through the pipe and disrupts the electrical path. He may himself become the electrical path.

Please do not use random locations of the plumbing as equipment grounds.

 

John is absolutely correct in his expalnation!

 

Well, I guess we will have to agree to disagree:

All of the if scenarios are possibilities......only.....and anything
catastrophic CAN happen. I could give perhaps a 1/2 dozen more.

The thing is that you have to make an assumption that there is
bonding, and grounding as required. I certainly would check for
that in advance of using H2O piping for ground.

The main problem I have with this is that on an application level,
the level of the real world that we live in on a day to day basis,
the same considerations that you mention would also apply to the grounded wall of electrical conduit. It can be cut, damaged, interrupted, improperly made up, fittings loose, resistive. Etc, etc. etc. It is steel, and copper is a better, less resistive, metal,
but it is considered an acceptable and safe grounding path.
When it gets a fault current on it, every grounded part in the system has a fault current on it until the breaker trips. So
your therory, simply does not pan out. The electrician in that case
may become the path to ground rather than the plumber.

If a plumbing line is defective, it leaks water and you can see it.
If a electrical conduit is "leaking electrons" you cannot see it. So
in some ways using the plumbing electrode is safer than the grounded wall of the conduit. At least it gives a visible indication
of it's being defective.

One last thing, when the first 5' of the water pipe ground has a fault current on it, the entire system has the fault current on it.
Test it out if you don't believe me. No, current doesn't "wander
around" but it is potential difference (to ground) throughout the entire system. Otherwise, your example of the kitchen faucet just doesn't hold water.

Anyhow, great talking to ya.....all food for thought.

 

I agree with the statement that conduit has the same drawbacks as copper or galvanized waterline in reguards to its mechanical continuity. It is far more likely for a water line to be replaced with a piece of pvc somewhere down the road but I doubt if someone will cut into a piece of conduit and replace it with pvc pipe. But if the conduit system becomes energised it is less of a hazzard in that there is far less exposed energised parts to contact accidently. If a conduit became energised in a bed room and it was not electrically continuous what are the hazzards? The screw holding the wall plate is the only exposed energised part.

Now if I ground my garbage disposal to a water line below my sink and the copper or galvanized waterline has been repaired with plastic somewhere down the line. What are the new hazzards? The entire stainless sink and faucet are energised and contact with any grounded apliance and the sink would be deadly. It is not uncommon to load a dishwasher with one hand and be reaching into the sink with the other.

I know these all sound like outrageous scenerios but it can happen, and my 9 yr old daughter and her 5yr old brother like to help with the dishes and I am not going to take any shortcuts that may endanger their lives.

I know it sounds like I am preaching but if its worth doing it's worth doing right. safety is no place to skimp.

 

There have been two posts in the last few months of people being zapped in their shower that were traced back to a local ground to the water pipe. 'nuff said.

 

My closing comments:

Grounding at the point within 5' of the entry of the H2O to the
residence is probably not a bad idea. Keep in mind, though, that the underground lateral is, little by little being replaced by PVC so the real ground is more and more the derived system (ufer or rod)
not the H2O.

We can go on all day here, scenario after scenario.......it is at best a judgement call, and dealing with inspectors in the city of SF week in and week out (one of the tougher jurisdictions in the U.S. ), they are not of one mind either.

So go ahead, do it your way.....it is always interesting to me when
someone trys to prove a point by talking about protecting childern or zapped in the shower. I could bring in as many situations that are equally dramatic just to prove my point.
I'm not going to.

Using a copper water pipe ground is still, by far my preferred method. Anywhere in the system. I like the use of the conductive wall of the copper, the fact that it is filled with a somewhat conductive fluid, and most of all when I apply the
appropriate measurements, I get a great ground reading. That,
to me serves my customer.

 

Dont forget this is a DIY forum. Yes, Im sure you would check for proper bonding, but if you didnt know to, you wouldnt.

Do you disagree with my interpretation given earlier in my first post? The way I read it, its illegal to use the pipe anywhere in the system (except the first 5'). Am I reading something wrong?

 

A DIY'er who doesn't know that there is a dielectric fitting along the water line will be in for a surprise. Codes are just a minimum requirement. As restated here countless times, backstabbing cheap outlets meets code.

 

Let me see if I have this straight:
The grounding electrode system involves the process of bonding the panel ground bar to an acceptable ground (e.g. 1st 5' of water pipe, and/or grounding rods), while the equipment grounding system involves grounding equipment (mostly through the grounding of recepticles) to the ground bar in the panel.

Is this right?!?!?!

 

Grounding to a water pipe will make the potential of the water pipe the same as the potential as the ground wire. That will be throught the house. So if they ground wire would become energized, the whole water system in the house will be energized. Of course, there is resistivity and you loose some voltage at the "far end", but it's basically the same. However, the current will choose the path of least resistance, so if the current can more easily flow toward the "groudn" as opposed through a person that let's say touches a pipe, then it will flow that way. Some current will still flow through the person, but the majority won't. You have to remember that if there is no current flow you don't get shocked. Every time you touch something metallic that's grounded you're basically putting yourself in parallel with the "true" ground of the house electrical. If your resistance is 10 ohms, and the panel's resistance is 1 ohms, and there is a fault, then 1/10 of the fault current will try to flow through you, and 9/10 will flow through the ground pipe/rod. Generally though less curren will flow through you. But both you and grounding point will have the same voltage "applied". It's a simple electrical circuit.