Bonding & Grounding

[smalljobs]

What is the NEC recognized grounding medium?
Our local inspectors require a # 4 wire to be run to the water line and a # 6 wire to the ground rods. If a # 6 wire to the rods is acceptable, isn't this considered 'bonding'? If the water line requires a # 4 wire because it is considered the 'grounding medium', don't the ground rods become the 'grounding medium' if the metal water line is replaced with plastic? Then isn't the # 6 wire unacceptable?

 

[derwith]

Re: Bonding & Grounding

If you have any 100 to 4000 or more amp service, you are only required by the NEC to install a #6 copper wire to a ground rod.

 

[hurk27]

Re: Bonding & Grounding

Smalljobs
The reason you are only required to run a #6 to a made electrode if it the sole connection to the electrode is Earth resistance is too high to cause any high current that could cause damage to it. Lightning is such a fast event it does not have time to heat the conductor and if a primary line was to make contact with the service drop they are protected at such a low amperage that it would also protect the #6. and despite all the myths the grounding electrode is only there for these two possibilities, not for faulting fuses, breakers, or any thing else.

 

[tom baker]

Re: Bonding & Grounding

SmallJobs: Get your self a copy of Mike Holts Grounding and Bonding text. It will explain the reason quite clearly.
The connection to the water line is a full size GEC as the water line, if it qualifes as a grounding electrode (ten feet in contact with the soil), full size per table 250.66 based on the size of the ungrounded conductors. this conductor could possibly carry a large amount of current in a lightning strike. The GEC to a made electrode is based on section 250.66 which modifies table 250.66 by allowing a maximum of 6 AWG to a ground rod. You can install a larger if you want and sometimes there is an advantage to using 4 WAG. And table 250.66 allows as small as a 8 wag but there is no advantage in using an 8, as it has to be physically protected.
The above are for grounding
However, if the water line does not qualify as a 250.52(A)(1) grounding electrode, then the connection to it is a bonding connection per 250.104, and this connection to creat a low impedance path to the circuit source to open the OCPD in a fault condition.