Grounding

[pdesai_pe]

situation: Main Electrical Service, Auxilliary service for Emergency lighting and power, and fire pump service.

The main service feeder is 480/277V, 2000 amp at 100% main rating and fed from utility T/R using 6 sets of 4 # 600 MCM in 4" conduit and grounded at the service entrance switchboard to ground rod using 4/0 ground and 1/500MCM at the main water pipe

Auxiliary service is only 480V, 3 phase, 3wire connecting to indoor, 45KVA-480V-208/120V lighting power transformer and tapped the source at the utility T/R using 3 # 3, 1#8 ground in a 1" conduit.

Fire pump service has 480V, 3phase, 4wire connecting to Fire pump and Jockey both have disconnect and controller fed from the utility transformer using 3#3/0, 1# 4 ground in 2" conduit. Jockey pump is tapped from the fire pump feeder ahead of the fire pump controller and have local disconnect.

Utility transformer systems grounding is established using 4/0 ground wire at the transformer.

Questions:

1. Please comment on the grounding methods.
2. Do I need to establish system grounding at all three services or the extended ground wire connected to the transformer grounding system is acceptable?
3. Service grounding for all three services is acceptable method and sized appropriately?

 

[GG]

Re: Grounding

Originally posted by pdesai_pe:
grounded at the service entrance switchboard to ground rod using 4/0 ground

#6 is the largest size wire the code reqiures you to run to a ground rod. 250.53(E).
Using table 250.66 I show that you only need a 3/0 to your CWG and not a 500Kcmil. 6 X 600Kcmil= 3600Kcmil. Table 250.66, over 1100Kcmil requires a 3/0 GEC.

[ July 19, 2005, 04:34 PM: Message edited by: GG ]

 

[lile001]

Re: Grounding

Originally posted by pdesai_pe:
situation: Main Electrical Service, Auxilliary service for Emergency lighting and power, and fire pump service.

The main service feeder is 480/277V, 2000 amp at 100% main rating and fed from utility T/R using 6 sets of 4 # 600 MCM in 4" conduit and grounded at the service entrance switchboard to ground rod using 4/0 ground and 1/500MCM at the main water pipe

Grounding seems kind of lightweight. The code requires you to connect the ground to all of these methods, if available: Concrete encased electrode, building steel, ground ring, and so on. At minimum I would specify that the ground is bonded to building steel, a ground rod is driven at the four corners of the buidling and bonded to building steel, and I'd specify a 20 foot rebar be turned up out of the concrete so it can be bonded.

Auxiliary service is only 480V, 3 phase, 3wire connecting to indoor, 45KVA-480V-208/120V lighting power transformer and tapped the source at the utility T/R using 3 # 3, 1#8 ground in a 1" conduit.

Fire pump service has 480V, 3phase, 4wire connecting to Fire pump and Jockey both have disconnect and controller fed from the utility transformer using 3#3/0, 1# 4 ground in 2" conduit. Jockey pump is tapped from the fire pump feeder ahead of the fire pump controller and have local disconnect.

Utility transformer systems grounding is established using 4/0 ground wire at the transformer.

Questions:

1. Please comment on the grounding methods.
2. Do I need to establish system grounding at all three services or the extended ground wire connected to the transformer grounding system is acceptable?

I would bond them all to the building steel and to the building foundation rebar, effectively bonding them together. No need to run a wire between all the services if you can use these other methods.

3. Service grounding for all three services is acceptable method and sized appropriately?

The wire sizes are OK, it is the number of grounding methods I would have an issue with.

 

[iwire]

Re: Grounding

Originally posted by lile001:
At minimum I would specify that the ground is bonded to building steel, a ground rod is driven at the four corners of the buidling and bonded to building steel, and I'd specify a 20 foot rebar be turned up out of the concrete so it can be bonded.

I assume you are stating what you would like not what the code requires?

Do you have a reason for ground rods at all four corners?

I am just curious what they will do for us?