Question:
A switchboard is rated 1200A, 480V, 3-phase. The service entrance conductors are 3-sets, 4- 600MCM.
I have called out for dedicated runs from the switchboard ground or neutral bus to (with the two having a main bonding jumper):
1) metallic cold water pipe ground electrode conductor using 1#3/0 BC
2) building steel using 1#1/0BC
3) concrete encased rebar mat using 1#4Cu
4) (2)- ground rods minimum 6ft apart with 8ft in earth using 1#4Cu
Note: All of the above are individual homeruns back
I thought that the main grounding electrode conductor would be the #3/0 from the water pipe to the ground bus (full size) with the other dedicated runs being supplemental ground electrodes per 250.53(D)(2) of conductor sizes as listed in 250.52(3) & 250.66(B) for concrete encased electrodes, 250.53(E) & 250.66(A) for ground rods. The building steel is used as a supplemental ground electrode and was not full size.
Also the 2005 NEC code alternative allows running back to a ground bus for the bonding jumpers. Can the switchboard ground bus serve this purpose?
The electrical contractor says that all the runs now need to be #3/0. Is he correct? Why?
Please tell me if I?m incorrect and provide the code sections that are applicable.
A switchboard is rated 1200A, 480V, 3-phase. The service entrance conductors are 3-sets, 4- 600MCM.
I have called out for dedicated runs from the switchboard ground or neutral bus to (with the two having a main bonding jumper):
1) metallic cold water pipe ground electrode conductor using 1#3/0 BC
2) building steel using 1#1/0BC
3) concrete encased rebar mat using 1#4Cu
4) (2)- ground rods minimum 6ft apart with 8ft in earth using 1#4Cu
Note: All of the above are individual homeruns back
I thought that the main grounding electrode conductor would be the #3/0 from the water pipe to the ground bus (full size) with the other dedicated runs being supplemental ground electrodes per 250.53(D)(2) of conductor sizes as listed in 250.52(3) & 250.66(B) for concrete encased electrodes, 250.53(E) & 250.66(A) for ground rods. The building steel is used as a supplemental ground electrode and was not full size.
Also the 2005 NEC code alternative allows running back to a ground bus for the bonding jumpers. Can the switchboard ground bus serve this purpose?
The electrical contractor says that all the runs now need to be #3/0. Is he correct? Why?
Please tell me if I?m incorrect and provide the code sections that are applicable.
