Advice for a typical 400 amp residential service

[iwire]

Re: Advice for a typical 400 amp residential service

Originally posted by suemarkp:
My point was I don't see how declaring the water feed to be plastic reduces the number of other ground electrodes.

I am still not following you, maybe we are just mis-communicating.

If the water pipe is not an electrode you do not have to supplement it.

Strictly speaking a service only has to have one electrode.

 

[suemarkp]

Re: Advice for a typical 400 amp residential service

It goes back to where Larry Fine said this: "Around here, the attitude is that, if you can't prove the pipe is metal, it's assumed to be plastic. Two rods, if you please."

I don't see how proving the pipe is metal -vs -plastic affects the "two rods please" statement. I see the ground elecrode requirement as the same regardless of whether the feed is plastic or metal. The only thing that changes is the location of the clamp.

 

[iwire]

Re: Advice for a typical 400 amp residential service

I am still missing it but it could just be me.

What we have here is a failure to communicate.

 

[LarryFine]

Re: Advice for a typical 400 amp residential service

A case in (my) point:

Two years ago, I did a typical 200-a upgrade, and tied my #4cu to the copper water pipe one foot out of the earth, in the crawl space. A single rod is all that would normally be required to supplememnt this.

Upon inspection, I was asked (rhetorically) to prove that the copper continued ten or more feet unbroken underground, which I obviously chose not to do. A second rod satisfied the inspector, cheaper*.

*Cheaper than exposing the pipe.

A while later, in a mixed-use building with an 800-amp service, they were installing a new 2" copper water service from the street. I called for service inspection while the entire run was exposed.

The inspector said he'd "like to see a second rod", but agreed that I was correct, that it was not required. I have always had a non-combative, mutually-respectful relationship with inspectors; one of us is right in the end.

 

[suemarkp]

Re: Advice for a typical 400 amp residential service

Not true. You still need two rods to supplement the water pipe unless you can prove the first rod is 25 ohms or less. That rule caught me too, as I didn't think you needed two rods with a water pipe ground. But you do.

 

[macmikeman]

Re: Advice for a typical 400 amp residential service

Not true. You still need two rods to supplement the water pipe unless you can prove the first rod is 25 ohms or less.

I agree with this statement.

 

[George Stolz]

Re: Advice for a typical 400 amp residential service

Originally posted by LarryFine:
Upon inspection, I was asked (rhetorically) to prove that the copper continued ten or more feet unbroken underground, which I obviously chose not to do. A second rod satisfied the inspector, cheaper... than exposing the pipe.

I am fairly confident (depending on my frame of mind immediately prior to the conversation) that I would either
a.) Give the inspector a sardonic look, shake my head, and walk away, or
b.) Make strangled cat noises as a blood vessel burst in my head, or
c.) Advise him to ask the plumber who installed it.

PS Larry - They're right, it's technically two rods regardless.

 

[eprice]

Re: Advice for a typical 400 amp residential service

250.53(D)(2) requires any ground rod acting as a supplemental electrode for a metal water line electrode to meet the requirements of 250.56 (the 25 ohm test). Therefore, as Mark has been saying, the presence of a metal water pipe as a grounding electrode, or the lack thereof does not effect the number of ground rods required.

If a Ufer ground is present, no rods are required in any case. If the water line is metal, a Ufer ground is sufficent as a supplemental electrode. If the water line is plastic, a Ufer ground is sufficient as the only electrode.

If a Ufer ground is not present, then two ground rods are probably required (unless there is some other electrode present that we have not considered). If the water line is plastic, a ground rod is required (two unless 25 ohms or less can be proved). If the water line is metal, a ground rod is required as a supplemental electrode (two unless 25 ohms or less can be proved).

[ October 03, 2005, 12:41 PM: Message edited by: eprice ]

 

[LarryFine]

Re: Advice for a typical 400 amp residential service

Originally posted by georgestolz:
PS Larry - They're right, it's technically two rods regardless.

I agree, and I guess I was lucky I wasn't asked to prove the resistance.