- Location
- New Jersey
- Occupation
- Journeyman Electrician
Why we can run a #6 to the ground rods (for a 4000 amp service) and not run a #6 to the water pipe?
GEC to Ground rods Vs. Water Pipe
- Thread starter infinity
- Start date
- Status
My understanding is the water piping system is a larger metallic network in contact with the earth compared to the rod. So it does not matter if you run a larger wire to the rod it can handle only X amount compared to the water piping system.
Engineers of the group will set me straight if this is BS.
Engineers of the group will set me straight if this is BS.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Basically my understanding as well. Sure a water pipe or building steel electrodes will vary in how much conductivity to earth they have, but will almost always be more conductivity then rod and pipe electrodes, CEE's, and ground rings.
At some point I believe someone has determined a typical ground rod/pipe can not dissipate more energy into earth then a 6 AWG copper can deliver to it. Similar for 4 AWG and CEE's or 2 AWG and ground rings.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I agree that the #6 is adequate because of the reason that you've mentioned but then why is the rod acceptable at all if it's the only electrode? If I need a big fat conductive water pipe to properly serve as a grounding electrode then why should the rod and #6 ever be acceptable?
Could this have something to do with the requirement to bond the water system piping? Seems that when used as an electrode it does double duty by complying with 250.104.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Some rules just are. There is no really good reason for them.
ptonsparky
Tom
- Occupation
- EC - retired
Left over from days of metallic pipe only?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
If a water pipe, building steel or a CEE are present you must use them. If not you must provide other type of electrode. Water pipe, building steel and CEE will all have less resistance then most other made electrodes and will be able to take on more current should conditions develop to allow that current to flow.
If the rod is over 25 ohms we must supplement it - but if second rod still leaves us over 25 ohms, they don't make you add any more - some places you can add several and still not achieve 25 ohms. This also leads up to the more recent wording where you can just add second rod and not have to measure resistance and call it good.
- Location
- Illinois
- Occupation
- retired electrician
Where you have a common underground water piping system, something that is rapidly going away, you have solid metallic connections back to the utility secondary grounded conductors. You can lose the service neutral when you have this solid connection and have no indication that the neutral has been lost. I believe the GEC sizing is to make sure it can carry the full grounded conductor load without heating up enough to cause a fire.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Yet not all underground metallic piping is networked throughout entire cities/neighborhoods. Old farmhouse on it's own private supply system won't necessarily have as low of resistance to earth as a municipal system that is all metal has. It won't give alternate paths to as many service neutral conductors either.
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