#6 for ground rod

[ryan_618]

2002 NEC art. 250.66 (A) states that the GEC to a rod "shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire". It is my understanding that the reason for this is that a 5/8" X 8' is limited in its functionality. With this in mind, If the engineer specifies a 3/4" X 10' rod with, say, #2, is this enforcible? Does it work better than a #6 on a 5/8" X 8'? Does the term "shall not be required" apply to both the AHJ and the engineer of record? Thanks in advance for your replies.

 

[dereckbc]

Re: #6 for ground rod

Ryan, the words "shall not be required" only means the NEC does not require it to be any larger. However if an engineer specifies the cable to be larger than a # 6 there is nothing to prohibit it.

I have seen many ground rings with rods, and rod counterpoises that use 2/0 and larger cable. So if you have a specification calling for a number 2 AWG you should use it

 

[jake benninger]

Re: #6 for ground rod

Note that the National Electrical Safety Code requires a minimun #4 for the GEC to ground rods. Since there is often a question as to which standard applies, many owners standards and hence engineering specifications require a minimum #4 or larger.

 

[tom baker]

Re: #6 for ground rod

The reason that only a 6 AWG is required is that the impedance of the ground rod is fairly high and a larger conductor serves no purpose, esp as the purpose of the ground rod is not for fault clearing (as it may be under the NESC) but to stablize the voltage and protect against overvoltage from lighting or line surges. Lighting doesn't need a low impedance path anyway.

However a larger conductor such as 4 AWG is required if the GEC is exposed to damage. Often 4 AWG is used as that is "on the truck".

I use 2 AWG to copper clad ground rods as they are for a radio antenna mast and I find the 2 AWG to hold up better when direct buried.

 

[charlie]

Re: #6 for ground rod

Jake, NESC rule 093C requires #12 minimum for instrument cases and secondary circuits for instrument transformers, #6 minimum for primary surge arresters, and #8 minimum for equipment, messenger wires, and guys. The other requirements are performance based and not prescriptive. That is why IPL uses #6 for their distributions pole grounds and #4 for their transmission pole grounds. All the sizes I gave are copper.

 

[ryan_618]

Re: #6 for ground rod

Thanks everyone