size of grounding / bonding conductor

[JDB3]

I had read somewhere about the largest necessary wire to go to ground rod is #6. If this same wire also bonds to the re-bar in the foundation steel, is #6 still permissible? Code reference please. And if not, why would a larger size be required to go to the re-bar? :?

 

[mwm1752]

see below

 

[mwm1752]

250.66 Size of Alternating-Current Grounding Electrode Conductor
The size of the grounding electrode conductor at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system of a grounded or ungrounded ac system shall not be less than given in Table 250.66, except as permitted in 250.66(A) through (C).
(A) thru ( c) are electrodes with max sizing.

350 MCM conductor for laterals - grd rod to MDP 6#CU, UFER to MDP 4#CU, Water pipe to MDP 1/0 CU -- grd rod to UFER 6# CU, UFER to WP 4# CU, WP to mdp 1/0 CU -- WP to UFER 1/0 CU, UFER to grd rod 1/0 CU, grd rod to MDP 1/0 CU you cannot reduce the size of an electrode condcutor if run in series with other electrodes. Min size for the specific eletrode applys to the specific electrode only.

 

[ActionDave]

I had read somewhere about the largest necessary wire to go to ground rod is #6. If this same wire also bonds to the re-bar in the foundation steel, is #6 still permissible? Code reference please. And if not, why would a larger size be required to go to the re-bar? :?

250.66(A) for ground rod, #6.

250.66(B) for ufer, #4.

Why? I dunno.

 

[JDB3]

Thanks, I know that is what the code says. Can anyone shed any light as to why the different sizes? :?

 

[GoldDigger]

Thanks, I know that is what the code says. Can anyone shed any light as to why the different sizes? :?

The higher resistance of a typical rod ground, and the better resistance of a UFER ground but not as good as the typical water pipe mean that the GEC resistance is less important and the largest fault current through those electrodes will be lower for an identical fault. No need for larger wires.

 

[retire09]

I have heard the reason is that some degree of corrosion is expected of copper in direct contact with steel and concrete.