Grounding electrode conductor

[massivek]

I am going around with an electrical eng. right now and getting more confused. On his drawings by the 4160 xfmr he has a 350 kcmil ground. Is this the ground conductor or the grounding electrode conductor? He refers me to section 250-122 for the sizing. Im looking in a california code book and not the NEC so im not sure if there is a difference. But the one i have says nothing about sizing. Please Help. John

 

[bphgravity]

Grounding Electrode Conductors are sized per 250.66 of the NEC, Equipment Grounding Conductors are sized per 250.122 of the NEC, and the Grounded conductor is sized per 220.61, 215.2(A)(1), 250.24(C)(1) of the NEC.

I am not sure what conductors you are referring to based on your post details...

 

[charlie b]

On his drawings by the 4160 xfmr he has a 350 kcmil ground. Is this the ground conductor or the grounding electrode conductor?

A "Grounding Electrode Conductor" (i.e., the wire attached to the ground rod or other electrode) never has to be bigger than 3/0 (copper). That is in Table 250.66.

An "Equipment Grounding Conductor" (i.e., the wire that connects the external metal parts of a piece of equipment back to the Ground Bus at the main service panel) is sized, using Table 250.122, on the basis of the overcurrent protection device for the branch circuit or feeder that provides power to that piece of equipment. In order to require a 350 MCM EGC, the overcurrent device would have to be at least 2500 amps.

So I am not certain what is going on here. To what is this mysterious wire connected at each of its ends? If it's an EGC, where is the 2500 amp overcurrent device, and to what is it supplying power? If it connects to an electrode, then why does this engineer think that a 350 MCM is needed?

 

[Bill W]

A "Grounding Electrode Conductor" (i.e., the wire attached to the ground rod or other electrode) never has to be bigger than 3/0 (copper). That is in Table 250.66.

An "Equipment Grounding Conductor" (i.e., the wire that connects the external metal parts of a piece of equipment back to the Ground Bus at the main service panel) is sized, using Table 250.122, on the basis of the overcurrent protection device for the branch circuit or feeder that provides power to that piece of equipment. In order to require a 350 MCM EGC, the overcurrent device would have to be at least 2500 amps.

So I am not certain what is going on here. To what is this mysterious wire connected at each of its ends? If it's an EGC, where is the 2500 amp overcurrent device, and to what is it supplying power? If it connects to an electrode, then why does this engineer think that a 350 MCM is needed?

Careful here: 250.30(8)(a) 12 1/2% for phase conductors paralled or otherwise that equal 1100kcmil.

 

[infinity]

Careful here: 250.30(8)(a) 12 1/2% for phase conductors paralled or otherwise that equal 1100kcmil.

250.30(8)(a) is for the grounded conductor not the GEC.

 

[Bill W]

250.30(8)(a) is for the grounded conductor not the GEC.

My bad...there is another section I haven't found yet that talks about 12 1/2 percent when feeders are increased in size...this would be equipment grounds however. I must say, though, I've spent more time in the book tonight than I have in awhile. Thanks to all the discussion.

 

[bkludecke]

I'm pretty new at this computer stuff and even worse at this forum stuff. I have a powerpoint presentation which is very simple and makes grounding and bonding issues clear to the average engineer and electrician. It was produced by a grounding/bonding guru in San Diego, CA I if anyone would like a copy of it, contact me on the side and I will see if my wife can email it to you. It is based on the '99/02 NECs but the basics never change.

Bob on the left coast.

 

[petersonra]

There are a lot of people who believe that you can get rid of electrical noise by making the ground wire larger. I have never understood that kind of thinking, but it is pretty widespread.

 

[tom baker]

Grounding for noise is a seperate issue than grounding as done in Art 250.
"Noise" is typically reduced by bonding metal parts together with a copper strap, to reduce impedance at higher frequencies than 60 hz.