G&B of a separtate structure, Does an GEC ever need to be larger than an EGC?

[cohosilver]

Background: There is a 225A SQ-D QO panel mounted to the side of a metal 8'x20' conex fed by a 4/C-4/0 w/#4 ground direct burial cable. The #4 EGC is connected to the ground bus in the QO panel. The AHJ requires that there be a ground rod, even though it may be argued that the metal conex sitting in direct contact with the earth can be considered a structural steel grounding electrode. So, I must bond the metal conex and have a GEC to a ground rod(s).

In researching 250 extensively the debate centers around what size of GEC needs to be connected to the conex. One side states that the GEC does not need to be larger than the EGC, therefore a #4 awg cu GEC to the conex is acceptable. The other side states that 250.104(C) and 250.104(D) require the GEC to be sized by Table 250.66 requiring it be be a #2 awg cu.

What say you? And provide your references. Thanks.

 

[don_resqcapt19]

First, the code never requires the grounding electrode conductor to a ground rod to be larger than #6. Second, the rules for sizing the EGC and GEC are independent and have no effect on each other.

 

[gndrod]

Background: There is a 225A SQ-D QO panel mounted to the side of a metal 8'x20' conex fed by a 4/C-4/0 w/#4 ground direct burial cable. The #4 EGC is connected to the ground bus in the QO panel. The AHJ requires that there be a ground rod, even though it may be argued that the metal conex sitting in direct contact with the earth can be considered a structural steel grounding electrode. So, I must bond the metal conex and have a GEC to a ground rod(s).

In researching 250 extensively the debate centers around what size of GEC needs to be connected to the conex. One side states that the GEC does not need to be larger than the EGC, therefore a #4 awg cu GEC to the conex is acceptable. The other side states that 250.104(C) and 250.104(D) require the GEC to be sized by Table 250.66 requiring it be be a #2 awg cu.

What say you? And provide your references. Thanks.

An EGC can not be used as a GEC [250.121]...thus the Service GEC is from T250.66. The conex would be considered equipment and not an electrode.

 

[cohosilver]

G&B of a separate structure

G&B of a separate structure

Okay, so to recap - EGCs and GECs are independent of eachother. Got it. I also got the 250.66A #6 awg cu to a ground rod. So, if I have a 225A panel mounted to a conex fed by (1)-4/C-4/0 awg + #4 awg cu direct burial cable and the EGC run with the feeder is connected to the ground bar. I have a #6 awg cu from the ground bar to a 3/4"x10' ground rod that has a 3/4" direct burial ground rod clamp and that portion is complete. The question I have now is does the bonding conductor from the ground bar to the conex need to be sized by T250.122 based on the 225A circuit breaker, or does it need to be based on 250.104(E) where it would be sized by T250.66? The question is whether the conductor size needs to be a #2 awg or a #4 awg? Where I am, the answer can affect hundreds of installations.