Bonding multiple service conduits? No GC

[jibron]

I'm still unclear.
I'm bonding four service supply side conduits feeding a row of four 400A, 480v switches to building steel and to the water supply.
Each switch has three 500mcm conductors.
There is no grounded conductor.

1.) Building steel is close. The water line is 50 feet away. Do I need to run an individual 1/0 to building steel from each conduit (something someone said the other day seemed to indicate that) or can I hit each conduit grounding clamp with a single unbroken 1/0 and then exothermic to building steel?

2.) How then would or could I handle the conductor to the incoming water line?
a) if 4 individuals, then one 1/0 cadwelded to the same I-beam and then to the water line?
b) if only one conductor, can I tap with irreversible "C" from the 1/0 to the water line clamp?

3.) I assume the bonding lug to each can would be 1/0 and "C" tapped to the conductor leading to building steel
Thanks

 

[Philip Barr]

First off your running equivilant to 2000kcmil (4x500) so you grounding electrode conductor your referring to will need to be 3/0 copper per 250.66.
As far as needing to run four of those from you Service disconnect to the building steel, waterpipe or any other electrodes no. You only need one common unbroken conductor run between your electrodes and into your disconnect. And as you mentioned terminated in an approved irreversable manner if you are needing to
make any "t's" or splices.

 

[Smart $]

My personal preference would be to run a 3/0 Cu to steel then jumpered to water line and tap off it at and to each of the disconnects with 1/0 Cu.

 

[Philip Barr]

Umm Im sorry I reread and it seems you have four seperate services if do then 1/0 is correct my apologies. Either way you can run one GEC to all your electrodes it's referred to as the common GEC in 250.64(D)(1) and then tap up to your switches in an approved manner

 

[infinity]

This is from the NECH. Your taps from the GEC to each switch do not need to be the irreversible type. A simple split-bolt is permitted.

 

[augie47]

As pointed out you are dealing with a total of 2000 kcmil of service conductors. As far as the conductor to the grounding electrodes (building steel & water) Per 250.66, you can run a 1/0 from each enclosure, or you can elect to run a 3/0 (largest required) to the electrodes and tap off with a 1/0 to each enclosure.
As far as your conduits are concerned, 250.102 comes in to play. IMO, you can run a 1/0 to each conduit for bonding, but if you elect to run 1 conductor and loop thru each clamp then you have to consider the sum (2000 kcmil) and go 12-1/2% for a 250 kcmil "common" bond jumper.

 

[Philip Barr]

Provided that said split bolt is listed for grounding and bonding

 

[jibron]

Thanks all, for the clarifications.
I guess I was missing or getting hung up on that "sum of the cross sectional areas" line.
Maybe I'm thinking wrong but I don't see it being likely that a fault would affect this installation in a way that would require a 3/0 to clear

 

[roger]

Thanks all, for the clarifications.

Maybe I'm thinking wrong but I don't see it being likely that a fault would affect this installation in a way that would require a 3/0 to clear

The GEC and GES is not for fault clearing.

Roger

 

[buddhakii]

There is no grounded conductor

Then what would clear a fault?

 

[roger]

There is no grounded conductor

Then what would clear a fault?

Nothing until a second fault occured.

Roger

 

[david]

I did not read the op to say that the 500 MCM is paralleled. I read this as four separate 400 amp disconnects grouped at one location. I?m not understanding why it should be considered 2000 MCM. My understanding is that you group the 400 amp disconnects in one location to keep a fault to a lower value in contrast to installing a 2000 amp service.
I believe it is correct that you only need one 1/0 grounding electrode conductor from one of the four 400 amp disconnects and you only need to tap the 1/0 GEC from each of the other three 400 amp disconnects. The taps in this case would also be 1/0

 

[david]

There is no grounded conductor.

Thanks

Why is that so?