Generator Grounding and Article 250.58

[hbendillo]

We have a project in my office for which I was not the original designer. The project has a 600 KW Standby Generator and two 4-pole automatic transfer switches. I know we have to ground the neutral at the generator but all that is shown on the riser is a ground symbol connected to the generator. There is not really any details or detailed instructions just basically follow the NEC. So I want to make sure it gets done right so I am planning to provided instructions to drive a ground rod at the generator, and bond the neutral at the generator. If I am interpreting correctly, according to 250.58 I need to bond the ground rod at the generator to the building service grounding electrode system. The generator is located outside, about 50 feet from the building in a weatherproof enclosure. So do I need bond my generator grounding electrode to the building ground with a grounding electrode conductor sized according to 250-66? The generator and service transformer are located on opposite sides of the building but my ATS's are located in a room next to the main switchboard. Can I bring the GEC from the generator to the main switchboard ground bus?

The project is at a point where the building slabs have been poured so no way to easily get a conduit out of the building or the switchboard pad. Can I run the GEC from the generator with one of the feeders going to a transfer switch?

 

[petersonra]

We have a project in my office for which I was not the original designer. The project has a 600 KW Standby Generator and two 4-pole automatic transfer switches. I know we have to ground the neutral at the generator but all that is shown on the riser is a ground symbol connected to the generator. There is not really any details or detailed instructions just basically follow the NEC. So I want to make sure it gets done right so I am planning to provided instructions to drive a ground rod at the generator, and bond the neutral at the generator. If I am interpreting correctly, according to 250.58 I need to bond the ground rod at the generator to the building service grounding electrode system. The generator is located outside, about 50 feet from the building in a weatherproof enclosure. So do I need bond my generator grounding electrode to the building ground with a grounding electrode conductor sized according to 250-66? The generator and service transformer are located on opposite sides of the building but my ATS's are located in a room next to the main switchboard. Can I bring the GEC from the generator to the main switchboard ground bus?

The project is at a point where the building slabs have been poured so no way to easily get a conduit out of the building or the switchboard pad. Can I run the GEC from the generator with one of the feeders going to a transfer switch?

i think the enclosure is a structure and thus requires a regular GES that is not satisfied by a single rod.

 

[hbendillo]

i think the enclosure is a structure and thus requires a regular GES that is not satisfied by a single rod.

What other grounding electrode is available? We will be bonding the frame. I guess we could establish a UFER ground in the concrete pad. Wouldn't connecting to a point on the building GES satisfy any other requirements. The feeders to the ATS contain an equipment grounding conductor so we will in effect be tied to the GES of the building. But according to 250.58 it seems we need also need a GEC tied to the building GES.

 

[Gregg Harris]

What other grounding electrode is available? We will be bonding the frame. I guess we could establish a UFER ground in the concrete pad. Wouldn't connecting to a point on the building GES satisfy any other requirements. The feeders to the ATS contain an equipment grounding conductor so we will in effect be tied to the GES of the building. But according to 250.58 it seems we need also need a GEC tied to the building GES.

250.30 Grounding Separately Derived Alternating-Current Systems. In addition to complying with 250.30(A) for grounded systems, or as provided in 250.30(B) for ungrounded systems, separately derived systems shall comply with 250.20, 250.21, 250.22, and 250.26.

250.50 Grounding Electrode System. All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used.