GEC

[lady sparks lover]

I'm sizing a GEC (grounding electrode conductor). The service conductors are 12 sets of 600kcmil wires for a 5000Amp service. Since the we have separate conduits for each set, can I just size the GEC for the 600kcmil or do I have have to use 12.5% of the total KCMIL. I know when sizing the neutral this applies, but does this apply to the GEC.

 

[petersonra]

Re: GEC

is it going to a water pipe?

 

[charlie]

Re: GEC

Lady, going to 250.66 which tells you to go to table 250.66, you will find that anything over 1100 kcmil Cu or 1750 kcmil Al is 3/0 Cu or 250 kcmil Al . . . period.

 

[charlie]

Re: GEC

BTW the reason for Bob's question (I think) is the reduction in size for GECs going to ground rods, ground rings, Ufer grounds, etc.

 

[lady sparks lover]

Re: GEC

Originally posted by petersonra:
is it going to a water pipe?

we are grounding the steel, the water pipe, the new section has an ufer ground to the rebar, and also we are driving a ground rod triad.

I came up with 2 set of 500 kcmil, but I thought all the GECs have to be sized that way.


Lady

[ July 12, 2005, 02:29 PM: Message edited by: lady sparks lover ]

 

[infinity]

Re: GEC

The way I see it this is all that's required:
Steel-#3/0 Cu
Water pipe-#3/0 Cu
Ufer-#4 AWG Cu
Ground rod- #6 AWG Cu

 

[charlie b]

Re: GEC

I don't think the 12.5% comes into play here. You have to add up all the parallel conductors (i.e., 12 times 600, or 72,000), and compare it to the table. As the Other Charlie said, that number is beyond 1,100, so you only need a 3/0 copper.

But I don't quite understand your planned configuration. Are you planning to install the GEC in the same conduit(s) that contain the service conductors? If so, why? Is it's connection to the Grounding Electrode System going to take place at the same location as the source of incoming power? You can get from the Main Service Panel to one of the grounding electrodes that you have listed, without first going out to the point of origin of the service conductors.

 

[petersonra]

Re: GEC

Originally posted by infinity:
The way I see it this is all that's required:
Steel-#3/0 Cu
Water pipe-#3/0 Cu
Ufer-#4 AWG Cu
Ground rod- #6 AWG Cu

A #6 to the rods, a #4 jumper from the rod to the UFER, than a 3/0 jumper from the UFER to the water pipe and steel. Why does that just seem wierd to me.

 

[infinity]

Re: GEC

A #6 to the rods, a #4 jumper from the rod to the UFER, than a 3/0 jumper from the UFER to the water pipe and steel. Why does that just seem wierd to me.

Welcome to Article 250! Actually if you have a U-fer ground than the ground rods aren't required.

 

[iwire]

Re: GEC

Originally posted by petersonra:
#6 to the rods, a #4 jumper from the rod to the UFER, than a 3/0 jumper from the UFER to the water pipe and steel. Why does that just seem weird to me.

It seems weird because it is wrong.

You have to go from the service to all those items or you would have to go to the 3/0 stuff first then down to 4 AWG to uffer then down to 6 AWG to the rods.

If you want to go to the rods then uffer then steel and water the whole run would need to be 3/0.

 

[petersonra]

Re: GEC

does it actually say that anywhere? I looked and did not find that.

 

[infinity]

Re: GEC

I think that what Bob means is that in your scenario the #3/0 would have to start at the service. The way it's written it sounds as if you have the #6 from the service going to the rod.

 

[iwire]

Re: GEC

Originally posted by petersonra:
does it actually say that anywhere? I looked and did not find that.

Well it could be made clearer but it is there.

250.66(A) Connections to Rod, Pipe, or Plate Electrodes. Where the grounding electrode conductor is connected to rod, pipe, or plate electrodes as permitted in 250.52(A)(5) or 250.52(A)(6), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.

The same wording can be found in 250.66(B) and 250.66(C).

 

[lady sparks lover]

Re: GEC

Hey you're right..

The main GEC from the main panel should be by 250-66, and the 12.5% is for the main bonding jumper. This also applies to the grounding electrode conductor according to article 250-66.

I read this in the NEC handbook....

Lady