Grounding electrode conductor

[central1ny]

I am installing a new 200A meter socket and breaker panel and need help on how to run the grounding electrode conductor. I am using 4AWG stranded copper and (2) 8 foot, 5/8" copper grounding rods installed 6 feet apart.

My original plan was to just run a single conductor from the breaker panel to the first electrode clamp and then continue this to the 2nd electrode. But then the electrical guy at home depot said that I need to create a loop and double up the conductor. I am not sure which is correct. My existing meter has 2 cables coming up out of the ground and running to the breaker panel.

Should I run the single wire or is there an NEC code that requires doubling the wire? I already paid the $60 for the wire so I might as well use it if that is standard practice (don't think I can return the wire). If I do create a loop with the wire, looks like I need two clamps on each grounding rod per NEC 250.70?

 

[Gooch]

pass the wire through the clamp on the first ground rod(unbroken) then end on the second ground rod, done.

 

[Falcon67]

pass the wire through the clamp on the first ground rod(unbroken) then end on the second ground rod, done.

What my utility did when they grounded the house service entrance.

 

[Aceman]

Follow Gooch's advice. That's how everyone does it.

 

[theoldwizard1]

Not an electrician.

Why 2 ground rods ?

 

[Norcal]

Not an electrician.

Why 2 ground rods ?

If you cannot prove 25 ohms of resistance or less,(expensive testing equipment BTW) a 2nd rod is required. See NEC art. 250.56 If a 2nd rod is driven, that is all one needs to do.


Here is a copy & paste from the 2008 NEC.

250.56 Resistance of Rod, Pipe, and Plate Electrodes. A
single electrode consisting of a rod, pipe, or plate that does
not have a resistance to ground of 25 ohms or less shall be
augmented by one additional electrode of any of the types
specified by 250.52(A)(4) through (A)(8). Where multiple
rod, pipe, or plate electrodes are installed to meet the requirements
of this section, they shall not be less than 1.8 m
(6 ft) apart.

FPN: The paralleling efficiency of rods longer than 2.5 m
(8 ft) is improved by spacing greater than 1.8 m (6 ft).

 

[central1ny]

Not an electrician.

Why 2 ground rods ?

I am not an electrican etiher but I think the use of two grounding rods comes from the following NEC requirement. To accurately measure the resistance of the ground rod down to 25 ohms and prove compliance would be near impossible using a standard ohm meter. I think that variations in ground mositure would also come into play affecting repeatability of measurements.

250.56 Resistance of Rod, Pipe, and Plate Electrodes. A
single electrode consisting of a rod, pipe, or plate that does
not have a resistance to ground of 25 ohms or less shall be
augmented by one additional electrode of any of the types
specified by 250.52(A)(4) through (A)(8). Where multiple
rod, pipe, or plate electrodes are installed to meet the requirements
of this section, they shall not be less than 1.8 m
(6 ft) apart.

 

[theoldwizard1]

If you cannot prove 25 ohms of resistance or less,(expensive testing equipment BTW) a 2nd rod is required.

Here is a copy & paste from the 2008 NEC.

250.56 Resistance of Rod, Pipe, and Plate Electrodes. A
single electrode consisting of a rod, pipe, or plate that does
not have a resistance to ground of 25 ohms or less shall be
augmented by one additional electrode

Hmm ... so you have to measure the resistance between a grounding rod and "ground". I'm confused. No wonder it requires special, expensive, test equipment. If 2 ground rods make them happy ... make them happy.

 

[JimDon]

Megger Test!

 

[Racecarl]

Since my building project started after 2008, I came under the 2008 NEC, which means I had to tie into foundation rebar for a ufer ground. All my rebar is tied together so it was just a matter of finding a rebar to weld a rebar stub to. A quick trip to the rental store and a half hour with a rotary hammer drill and I found rebar and made the connection.

I made some floor pulls which are welded to rebars and connected to the rebar and mesh in the floor. The floor rebar is connected to the rebar in the foundation, so I used my Fluke 78 and found there was around 6.8 ohms resistance from my rebar stub to one of the floor pulls, so I knew this connection was good. I had easy access to an anchor bolt, which was not tied to the rebar. The Fluke showed several megaohms resistance, a nearly open connection.

I have an old BEHA megger (the old crank style) so I hooked it up the anchor bolt and the floor pull. It showed a connection--if I were checking underground wire insulation I would be looking at replacing the wire. Directly outside my shop is a small power pole that the gas company uses to power their cathodic(?) gas line protection equipment. Going from their grounding wire to my anchor bolt yielded nearly the same result from the floor pull to the unconnected anchor bolt. I then hooked up the megger to the rebar stub I attached to my rebar and that connection was MUCH better--a definite fault would be present if I was checking underground wire insulation. My Fluke meter showed slightly better connection, but not a definite connection. The distance between my foundation and the grounding rod was about 6'-7'.

 

[Norcal]

If you have a UFER, you don't need a driven rod unless you have the misfortune of a backwards PoCo, that is not a NEC issue though.