Grounding water and gas pipes. Why?

[puma guy]

I had the electrical service updated at a rent house a few years ago, new main box and weather head and mast, etc to meet code. The inspector insisted that two separate grounding cables and rod be installed on the 100 amp box. The electrician made the change w/o charging me after I bought the second grounding rod. I had no major problem with it though I mentally questioned the necessity. Fast forward. My brother has a house from the same era, same neighborhood, built in the 1950's and is having his service updated. He had estimates from several electricians and was told the city now requires that the water pipe and the gas pipe be bonded/grounded as well. I can't for the life of me figure what purpose or advantage grounding a pipe coming out of the same soil the bonding rod is in would be. I know some people used water and gas pipes as grounds in older houses that's the case here.

[RJGold]

As my dad says, "...ain't no reason, it's company policy...".

I would guess the grounding requirements are being updated to account for the fact that the gas and water feeds to houses are most likely non-metallic these days.

The part that's hard to understand is that you and your brother are being saddled with the newest code because you're having work done now. Your service lines may very well be metallic underground and would actually serve as grounds. Hence my dad's quote above. To keep from having to make decisions on any individual circumstances, the governing entity just says thou shalt do it this way from this point forward.

My two cents...

[Paul's Shield]

Maybe the friction or static charge it could create. any two different substance rubbing against each other could cause static friction. I could understand the gas line, but the water pipe I would have no clue why?

[Jim Beaux]

Insurance companies are pushing stricter code standards (wouldnt ya know it? ). The grounding/bonding requirements are necessary if the house has plastic plumbing.

[dave_in_austin]

How does one ground a PVC water pipe?

[Jim Beaux]

How does one ground a PVC water pipe?

You dont ground PVC, you ground the in house metal plumbing fixtures (and washing machine) that are insulated from making ground because of underground PVC service lines.

[dave_in_austin]

So when the statement was made that "city now requires that the water pipe and the gas pipe be bonded/grounded" it does not apply to the pipe, but rather the fixtures? Does this mean that every fixture in the house has to be individually bonded/grounded? I am interested in this because I am considering some remodeling and do not want to get trapped into bringing everything up to code if that will require driving a grounding rod at every metal plumbing fixture.

[Keith B]

Ground potentials can exist between various items even if they are in the same soil. This means if you have a voltage fault that exists in a circuit that looses it's main ground, the new path to ground may be the plumbing. If you somehow get across the circuit and the plumbing then the electricity will pass through you to ground. That is just one scenario. Bonding the pipes and electrical ground together means there is no chance of a new path to ground being established.

I built a house back in 1990 and did all of the wiring myself. While I totally met code for the house wiring, I made a mistake in forgetting to bond my radio tower to the power entrance ground. I ran the wire when I installed the tower, but somehow forgot to connect it to the power entracne. A couple of years latrer I had a lightning strike that hit the tower, but looked for a better ground and found it by going from the tower, through my equipment and to the electrical ground (path of least resistance). I lost several radios, a computer, a television and garage door opener that were all on the one circuit.

Here is a good basic explanation on why you should bond your grounds http://en.wikipedia.org/wiki/Electrical_bonding" onclick="window.open(this.href);return false;

[philip964]

Apparently in very large spread out buildings like airports, a potential can build up between grounds at least that is what I was told.

I always assumed the pipes were grounded to the ground rod so that the pipes going into the earth would assist the ground rod in case it ever failed to make a good ground.

[puma guy]

The water and gas lines are both metallic (galvanized for the H2O and black pipe for gas.) I had to have two separate ground rods on my rent house per the inspector's requirement. I had a new main box and there was an existing add on sub-panel with a 220v breaker for Central A/c. My electrician had separate ground cables from each box tied to one rod and the inspector insisted there be two rods. The rods were probably no more than 18" apart.
I've never heard of grounding individual fixtures but I am no expert. I guess you could ground each fixture since the supply lines these days are most often plastic hoses. All the fixtures in these old houses have metallic supply lines.
I guess he'll know for sure tomorrow when he has the work done.

[jimlongley]

OK, for what it's worth, I used to do grounding for the phone company, professionally. Ground potential can change over "shockingly" short distances (pun intended, first used in the 90s) and potential differences can do more than just lead to shocks and problems like Keith's (and not the first time I have heard that tale of woe) but low voltage potential differences can lead to electrolytic corrosion with pipes and ground rods almost literally melt away.

Bonding ALL of the grounds together is the best idea, using the largest practical ground wire. In the engineered applications that I dealt with quite often, the specific gauge wire was part of the calculation, depending on the joules of energy anticipated to be dissipated. And yes, I really used to talk like that.

For a typical household, #6 wire is probably the maximum, but also the minimum, required, although over shorter distances smaller gauge, like #8 or #10 would be ok.

Another thing to consider is the type of power you expect to need to dump to ground. All of this bonding is most effective at DC or low, as in household 60 Hz, frequencies. If you're a ham radio operator, or a cable TV provider, or any number of other things, effective DC to 60Hz ground might not be effective for your purpose.

And don't ever run a protective ground through a metallic conduit. Any metallic object, including a clamp, can act as a "choke" blocking certain frequencies from getting from the source to ground. A bunch of years ago I investigated a situation where our customer had noise affecting a digital switch (long story) and discovered that they had the ground cable for the switch run through a conduit, due to a misinterpretation of the building code, and once the situation was corrected, the noise went away.

[Pawpaw]

Although I have not researched it, I wouldn't be surprised to find the requirement to ground water and gas lines is intended to keep electricity (from lightning) out of your house.

It is a fact that lightning can strike the ground and electrify buried cables, injuring or killing someone 10 miles away. When I was in the Air Force, the rule was that if there was a thunderstorm within 20 miles of the base, all work on buried cables stopped.

The pipes that carry both gas and water are coated to prevent the salts in the ground from corroding them. This coating must work as an insulator, also. Perhaps not a good insulator, but an insulator nonetheless.

High voltage from a lightning strike could electrify your stove or other gas appliance. What if you happened to be in the shower when the event happened?

[Jim Beaux]

Im far from being an expert on this subject, but I am under the impression that a separate ground for each fixture is a no no. They have to all be bonded to a common ground.

I assume that it may have something to do with different potentials generating electrolysis. (Two dissimilar metals immersed in water creates a current which would accelerate corrosion.) This could rapidly deteriorate the anode in the hot water heater and then the corrode the tank.

Check the codes before you do anything or you may be looking at spending more bucks then you planned.

[MasterOfNone]

I suspect this is partly to address the unknowns from the past. Because it was common practice in the past to use the water line as a ground, that rental house could have such ground connections inside. Short of dismantling the whole house, you never know. And without digging up the service line, you don't know how far that water line goes into the ground before becoming plastic. So it gets grounded as a rule just to be safe.

[Keith B]

2008 National Electrical Code Section 250.52 increased the requirement to 2 metallic condcutors when using ground rods. This is to maintain the proper amount of earth contact, especially in dry or rocky soil. The rods must be properly spaced and bonded topgether with the proper AWG wire per the NEC. Here are a couple of articles:

http://ecmweb.com/bonding-amp-grounding ... -part-6-12" onclick="window.open(this.href);return false;

http://fyi.uwex.edu/mrec/files/2011/04/ ... EC2010.pdf" onclick="window.open(this.href);return false; (Electrode discussion starts on page 24)