Buildings Supplied by a Feeder or Branch Circuit

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Flapjack

Senior Member
Location
USA
Occupation
EE
Do both of these instances require a grounding electrode conductor terminated to the ground bus of the new panels per 250.32(A)?

An existing outdoor 480/277V generator that has a main breaker feeds a new MLO panel inside an electrical room in PVC conduit. The generator has a GEC and SBJ connection already and is about 20 ft away from the electrical room.

An existing 120/240V panelboard in a shop has a branch breaker with conductors in RMC conduit to a new panelboard in an electrical room. The electrical room is a separate structure about 15 ft away from the shop.
 
For the electrical building, 250.32(A) would require a grounding electrode system in the building. Reference 250.52 for the electrodes permitted for grounding of this building. All must be bonded together if they exist.

For the generator, is this separately derived? You say the generator feeds the MLO panel directly, is there not an ATS also connecting the MLO panel to the main distribution system in the building? For the 3-phase, 4-wire system you do not bond the neutral and ground bus together at the generator unless the neutral is switched at the transfer switch together with the phase conductors. If this generator is separately derived, the grounding electrode system is required. If it is not separately derived, the grounding electrode system MAY be installed as a supplemental grounding system....must be bonded to the equipment grounding conductor.
 

Flapjack

Senior Member
Location
USA
Occupation
EE
I guess the answer to my initial question is yes, they are required. The handbook commentary in 250.32(B)(2) cleared it up for me in regards to the generator.
I just don't understand why there isn't an exception that deals with the structures' proximity to one another.

The other scenario for the panel in the shop feeding a sub-panel in the electrical room just seems kind of ridiculous to me. The electrical room and the shop share the same grounding electrode system. If the electrical room were attached to the shop, then the rule wouldn't apply, but because the two nearby structures don't share a common wall, I need a GEC.

Yes, the generator is a separately derived system. The generator feeds a panel and the breakers in the panel feed manual transfer switches. The generator is required to have the neutral and ground bonded because the generator is provided with a breaker (first disconnecting means). The neutral is not brought to the panel.
 
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