Bonded ground wires vs. earth ground wire

[Eigenvector]

I asked the electrician why there was such a difference between the two types of wires but never got an answer other than "It's code".

So when I had my earth ground installed in my panel, 2 ground rods ~4 feet apart with a 10 gauge wire connected between them and the panel.

At the same time he installed bonding for the hot, cold, and gas pipes - but for this he used like 5 twisted strand 10 gauge wires - it was a HUGE copper cable.

When I asked why the bonding got the big cables and the earth ground got the single 10 gauge he mentioned that 10 gauge is really all that is required for good solid ground and that's what code called for. But he didn't really explain why the bonding required such massive wires. It's not like I think he cheated me on the copper, I trust the company he works for and he did very good frugal work in the panel. I just kind of want to know - why the difference in size? If anything I would expect the situation to be reversed, the massive cable to the ground rods and the small wire to the pipes.

[Tom The Great]

I think code now requires 6 or more feet and should have not been smaller than 6awg coper, but I'm not beating up the details. ;)

IMHO:

I'm thinking you need to have the work looked at by a qualifed electrician. The information you gave seems 'weird'. The bonding of piping shouldn't require such thick cable. Unless you have some monster water equipement.

Ok, now for some information. The cable going to ground rods aren't sized to carry fault current. They are sized to stablize voltages against transiants. The bonding of piping, and equipment(such as ground wires in circuits) is designed to carry max ground fault current back to the power source(the service panel, sub panel, etc) and cause the over current protector (a breaker, fuse, etc) to open. So you can see who one is to 'fix' voltage fluctuations, and the other is to protect equipment and lives, which results in different concerns (amps, etc).

Now this information was just an FYI, you need to have a qualified electrician to check your system, if you have ANY concerns about it's safety.

tom

[Eigenvector]

The company that did the work was qualified and greatly respected in the industry in my area. I trust the work they did. I may have the wire gauge sizing off, it might in fact be 6 gauge, but I've never seen wire that thick so I don't know for sure. All I know is that it wasn't 12 gauge or more. I specified code work, he confirmed that everything he did was to code. I'm not asking because I don't trust the work, but rather just out of curiosity. Not slapping you down for answering so don't take offence, I'm merely clarifying my position.

But your explanation of the purposes does help explain the sizing differences to me.

[Joseph Meehan]

First I don't know, nor did I look up the code. However I strongly suggest that you always should follow the code, especially when you don't understand why it is code. They don't write code without good reasons.

My guess (SWAG) is that at least some of those devices that are being bypassed may be damaged by the leakage and the larger cable will make sure the cable is the path of least resistance to protect them.

[J.A. Michel]

When using two ground rods, they should be seperated by a minimum of 6 feet. Also, 6 AWG wire is required when using ground rods, not 10AWG. If the work is done "to code" then this is how it should have been done. Did they pull a permit? Better verify what they did and what wire sizes they used.

Correct. 4AWG is required for bonding the pipes.

[John Grabowski]

The National Electrical Code requires that ground rods should be no less than 6' apart. However tests have proven that ideally for two eight foot ground rods a distance of 16' or more is best. I think that the minimum wire size for supplementary ground rods is #6. Depending on the size of the service your bonding jumpers can be #8 or #6.

I hope that this work will be inspected.

[volts500]

NEC and engineering studies have determined that a ground rod cannot dissipate any more electrons into the earth in a given time than can be carried by a #6 copper wire, thus there is no need to use a wire larger than a #6 copper for ground rod, pipe or plate electrodes.

Now I'm curious........what was used to ground your electric system before all this?

[Eigenvector]

You know I wasn't asking for a critique of the job, I was asking WHY the size difference between the two. Or do you not know, but you felt compelled to answer anyway?

In any case I got the answer I needed a couple posts back. Thanks for responding.

[Eigenvector]

The galvanized pipes. Basically nothing.

[Tom Horne, Electrician]

The galvanized pipes were undoubtedly connected to an underground metal water pipe that was metal to metal connected to a metal well casing or a public water system consisting of literally miles of pipe and you call that nothing. Underground metal water pipes of significant length or depth make a much better grounding electrode than those two driven rods you are asking about. The entire purpose of the two driven metal ground rods is to provide a backup to the water piping in case it is opened during plumbing work or replaced with plastic during a future repair. If your entire home were piped with plastic so that there was no metallic piping inside the home and the only metal piping was the underground metal water piping that supplies the building the code would still require that underground metal water piping of twenty or more feet in length be used as a grounding electrode.

[Eigenvector]

I see where you are coming from, and I have a feeling that this has been discussed at length ad nauseum, but I'm gonna ask anyway.

The supply pipes feeding my house are plastic not metal (I've been watching them install them all summer long, those 6"+ blue/green nylon plastic pipes. - I'm presuming those are water mains, I guess they could be sewer lines too but sewer lines are concrete usually. So how would bonding to the water mains help there? At that point there is no metal pathway except from my house to the meter. Not that I'm disputing your claim mind you, when I convert my house to PEX I still intend on having the inlet cold water pipe be copper - if only so that it's solid and secure. But if the water mains are plastic pipe, how would my house be bonded then?

Anyways we're getting off track here, so if you want to just point me in a good direction I can take it from there so we don't have to go over this topic again.

[J.A. Michel]

Sorry, didn't mean to make you mad, that wasn't the intent. I was just pointing out what the code requirements are vs. the information you supplied. I felt it was more important to point out a potentially unsafe situation than to state the reason for differing wire sizes. sorry.

[Eigenvector]

This is a newsgroup - it's filled with people that I've either pissed off, offended, insulted, or harassed.

So far as I'm concerned - everything that occurs here is water under the bridge when the day is done.

[Wayne Whitney]

A 6" diameter pipe leading to an individual residence will be a sewer pipe, not a water pipe. A water pipe will be 1" plus or minus.

Cheers, Wayne

[Eigenvector]

Well at least now I know my drinking water isn't as bad as I'd thought.

[gfretwell]

I imagine he is talking about the pipe at the street Green pipe is sewer, blue pipe is potable water, purple pipe is recycled water. It is true that any new water pipe will be plastic but in older neighborhoods it is metal. The larger grounding electrode conductors for water pipes is from those days when a water pipe was as good an electrode as you could get. The code never backed off of that, in spite of the fact that water pipes can't be trusted anymore and must be suplimented. If you do still have a 3/4 or 1" copper pipe going to the steet it is an excellent electrode and will sink every amp a #4 copper wire could source. Just be sure the connection is on the street side of the meter or anything else that could insulate it.

[# Fred #]

Does NEC do engineering studies like this? I see #4/0 and 250MCM bonded to ground rods and loops designed by system power engineers. Commercial or industrial facilities may have a grounded fault of 200,000A or more so do you really want to use #6?

[Member, Takoma Park Volunteer]

If your house is more then eight feet from the water line the metal service lateral will be longer then eight feet. Since it's entire length is installed below the frost depth it is at least likely to be a better electrode than the two eight foot long driven rods.

Be advised that many larger diameters of underground piping can be purchased with plastic linings and coatings. What appears to be plastic piping may be coated steal.

[volts500]

Do you really want to ground such a system with just a ground rod? Such systems usually use building steel and underground metal water pipes as the primary grounding electrode(s). Yes, as you stated, such systems do require the primary grounding electrode conductor to be larger, as do _houses_ when the primary grounding electrode is an undergound metal water pipe. However, even on those large systems, the sole connection to a ground rod is still only required to be a #6 copper, per (2002) NEC 250.66(A). You can connect a 250 MCM to a ground rod on such systems if you want, even Cadweld it, but it still won't dissipate any more electrons to ground than a #6 because of the limitations of the ground rod itself, as determined by engineering studies. IMHO, that's why ground rods suck, while they are better than nothing. Driving them deeper helps too.

For residential, 200 amps and below, IMO, it's easier to install bare #4 for the entire system ground, even for ground rods, because it avoids confusion and mostly because #4 doesn't require physical protection.

The OP wanted to know why a _smaller_ wire was ran to the ground rod. Sorry for not being clear.

[Red]

Recycled water?? That's a new one for me. Where does it come from & where does it go?