Grounding Electrode Conductor at Switchboard

[philly]

At an industrial site a new 480V Switchboard is being installed inside an electrical room. The switchboard is being fed from a 500kVA transformer with a 480V secondary (transformer is not service entrance).

The Switchboard will have a neutral and a Supply Side Bonding Jumper (SSBJ) coming from the transformer with the neutral connected to the neutral bar of the Switchboard and the SSBJ connected to the ground bus.

My question is weather or not the new Switchboard ground bus needs to have a Grounding Electrode Conductor (GEC) connected between the Switchboard ground bus and earth.

Typically In most Industrial settings that I do work in there is a ground grid that encircles the electrical room which consists of ground rods, and 4/0 copper wire which is tied into the foundations rebar at several points and has pigtails which come out of the concrete slab for connection to the ground bus of equipment sitting on the slab at various locations. I have worked on several projects where we have simply replaced equipment in the same location so we were able to disconnect these ground pig tails from the existing equipment and then re-connect them to the new equipment once it was set in the same location.

The issue I'm looking at now is that this new Switchboard is being located in an area of the existing electrical room where there are no ground pig tails and any of the existing ground pig tails sit across the room at other locations.

I'm not sure that these GEC's are required in a case like this but I believe it is always done as "good practice". Does anyone have any recommendations in a case like this on how to tie the new Switchboard into the existing ground grid? Would it be a good or bad idea to run an existing connection from either inside our outside the room to the Switchboard location for connection?

 

[don_resqcapt19]

Grounding electrodes and grounding electrode conductors are required for all separately derived systems. See 250.30.

 

[chris kennedy]

See 250.30(A)(4), (5) or (6) to determine if that clarifies it for you.

 

[Smart $]

You have to use the existing grounding electrode system and the GEC must run to the nearest of water pipe electrode or structural steel electrode, (assuming one of these exists).

 

[philly]

Grounding electrodes and grounding electrode conductors are required for all separately derived systems. See 250.30.

I agree with this. I guess the first thing that needs to be decided is weather or not the system bonding jumper will be located at the transformer (outside) or the Switchboard (inside) which will dictate where the Grounding Electrode Conductor (GEC) must be connected to. If I locate the system bonding jumper at the transformer then I can simply reconnect the existing grounding system pigtail to the transformer neutral since these pigtails do exist at the transformer locations from the previous transformers.

Is there a standard, or best practice as to locating the system bonding jumper at the transformer location vs at the first disconnecting means? I typically see it done at the transformer location but have seen a few rare cases where it is done at the disconnect. The Supply Side Bonding Jumper (SSBJ) is required in both cases so I guess the advantage of doing it at the transformer would be that you wouldn't have to run a neutral conductor to the disconnecting means if the system didn't require a neutral (a neutral would need to be run to first disconnecting means if system bonding jumper was located at first disconnecting means)

You have to use the existing grounding electrode system and the GEC must run to the nearest of water pipe electrode or structural steel electrode, (assuming one of these exists).

If the system bonding jumper is located outside at the transformer then I guess technically a GEC at the new switchboard would not be required? I have seen many installations however that have the system bonding jumper and GEC at the transformer but then at the secondary panel have another GEC between the ground bus and a bus bar in the room? Is this standard practice or overkill? I see this in a lot of panels with surge protective devices so perhaps this is an additional grounding requirement/practice for panels with surge devices?

Fed from the Switchbaord there is also a 480V panel which in turn feeds a 45kVA transformer and 120/208V transformer. For the GEC required at the 45kVA transformer I was going to recommend installing a Ground Bar on the wall and have this ground bar tied back into the existing ground grid/grounding system. I can then use this ground bar for connecting the GEC at the 45kVA transformer and a supplementary GEC from the switchboard if desired. Does this sound like a good idea?

 

[philly]

Another question that I noticed? I see very little plans that actually specify the size of the system bonding jumper and supply side bonding jumper. There is usually either no mention of these or there is a general detail which shows the connections and indicates that they should be sized per the appropriate NEC sections. This puts the responsibility on the contactor to size the bonding jumpers. I've seen a few plans here and there that actually detail the information for each one. I'm curious what others see or do?

Also rarely do I see on plans an indication weather or not the system bonding jumper should be located at the transformer or first disconnecting means so I guess its always assumed that its at the transformers?

 

[Smart $]

If the SBJ is located at an outdoor transformer, the GEC must be connected there. If the GEC/GES at the outdoor transformer is not of the same GES as the building, then it is required the building GES be connected at the building disconnect (EGC bus, no neutral bond).

Doesn't hurt to connect it there even when same GES is connected at transformer... but it amounts to being overkill as you said... darn near like running two SSBJ's.