ECN Forum Forums Code Related Discussion NEC & other Code issues Sub panel ground rod connection

Reno:

The 'logic' for the 2 rods....

Provide documentation that the 1 rod is 25 ohms or less....most if not all inspectors request documentation, signed & sealed by the EC with test procedure, tester used, etc.

or....drive a second rod & call it a day!

Cost of performing a ground resistance test, including labor & rental tester vs. cost of 1 additional rod, 1 acorn clamp, & 7' of wire. A basic no brainer.

On plan review, all I have seen have 2 rods specified.

I know that is the rule but one of my engineers always said if one rod won't get you 25 ohms, driving two is not going to help much.

I concur, if 1 rod is higher than 25 ohms, the dirt nearby isn't likely to be much more conductive.
However, Hotline's; right it's in the Code just that way.

To quote a sign that I saw at the FAA one day:
It doesn't need to make sense...it's the rule.

well i thought 250 said we have to connect to concrete, aka, a ufer now.....~S~

This Ufer thing really has to be addressed by the AHJ on new construction. If they don't require a Ufer inspection at the time the footer is poured it is not "present" and you don't have to break up concrete to get one.
In SW Florida it is part of the footer steel inspection. The places around me use the "turned up rod" method

Old link
http://gfretwell.com/electrical/ufer.jpg

Sparky:
Ufer here in NJ is required on new work. The inspection is the responsibility of the Building Inspector with the footing inspection. The 'turned-up' rebar is not accepted. And.....if it's missed...(oops), the concrete does not have to be disturbed.

if this were to happen, I would say there was something wrong with the main bond at the service. A grounding electrode system protects from external sources like failed transformers and near by ligthning strikes. The voltages are much higher so the earth's resistance is easily overcomed. If a fault as you described was cooking the the GES, that tells me the main bond is not doing what it is suppose to do.

Greg & Hotone,

i often am (unfortunatley) the ahj

i've been a big advocate of concrete bonding for decades

but i often need to sell what i'm doing to clients, and it has to make sense to them when i do

simplistically put (because most clients are turned off by tradespeak), a G-rod is a surface area of 1/2"x 8' , making to the 'crete assume the dwellings footprint of contact to earth

what's obviously a better job, and all that better job really takes is being there before the pour with the proper bonding bits/ pieces required....

why is more earth contact better than less ? better lightning protection, and voltage stability

where so many voltage anomolies exist that lessen the life of our sensitive electrical goods, i believe that small extra step is worth it......~S~

or it's a GEC acting as a nuetral , due to it's low R, and proximity to the serving Xformer sparkyinak

it can happen, especially with pad mounts

and don't you find a certain irony in the nec asking for a low R GEC, and then claiming the earth is not a conductor?

rather conflicting imho....~S~

I said earlier and it is really true. A lot of these distribution models were based on a world where the water pipe was your best neutral conductor and tied the whole city together. The earth was just something to support the pipe.