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#209851 05/07/13 04:45 PM
Joined: Jun 2012
Posts: 74
Member
Hi,
I am working on an ethanol plant and the ground grid is 4/0. From the ground grid to building steel and large stainless steel tanks they are using #2 XHHW for bonding..This is the GEC correct? They have also used this #2 from the grid to bond the case of some very large 4160V Motors..Should this not be sized by the largest OCPD?

Thanks
Greg


Don't drive and TEXT! Drive now TALK LATER!
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akmaster #209855 05/07/13 05:12 PM
Joined: Jul 2004
Posts: 9,643
G
Member
You use 250.66 to size ground electrode systems based on the service conductor size.
#2 gets you up to a 350Kcmil copper or 500Kcmil aluminum service conductor.
If the service conductor is larger than that you need a bigger GEC.


Greg Fretwell
akmaster #209857 05/07/13 07:33 PM
Joined: Apr 2002
Posts: 7,274
Likes: 2
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The 4/0 grid may be the GEC, or it may be a 'ground ring' that the various conductive items/equipment are 'bonded to'. ie: an equipotential grid. IF it is a 'eq grid', then it was designed or spec's by a PE/EE.

As to the motor case...sounds like a 'eq grid' to me.


Last edited by HotLine1; 05/07/13 07:33 PM.

John
akmaster #209858 05/07/13 08:07 PM
Joined: Jun 2012
Posts: 74
Member
Thank you very much!

Greg


Don't drive and TEXT! Drive now TALK LATER!
akmaster #209859 05/07/13 10:31 PM
Joined: Jul 2004
Posts: 9,643
G
Member
The GEC is the conductor that lands on the grounding bus bar in the service disconnect enclosure where the main bonding jumper resides. Everything else is a jumper or an electrode.


Greg Fretwell
akmaster #209865 05/08/13 07:39 PM
Joined: Jun 2012
Posts: 74
Member
#2 from 4/0 to building steel, tanks, or any motor..

Just does not look right to me..

I drive a ground rod run #6 to meter base this is the GEC correct? The GEC is run with circuit conductors..an equal potential grid is a grounding mat/grid connected to ground rods..for the whole plant they have 4/0 in the ground and #2 insulated ground for grounding tanks, motors or building steel..thanks for the replies..

Attached Images
2to4_0_tap_cr.jpg

Don't drive and TEXT! Drive now TALK LATER!
akmaster #209866 05/08/13 07:41 PM
Joined: Jun 2012
Posts: 74
Member
#2 from 4/0 to building steel

Attached Images
2gec_to_4_0_cr.jpg
Last edited by akmaster; 05/08/13 07:42 PM.

Don't drive and TEXT! Drive now TALK LATER!
akmaster #209867 05/08/13 10:06 PM
Joined: Jul 2004
Posts: 9,643
G
Member
The only way a GEC can be a #6 is if the only electrodes are rods. 250.66(A) says " that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG".
If this is going on to another electrode, the GEC must be sized to the best electrode you have in the system, up to what you get from the 250.66 table.

From the handbook

[Linked Image from gfretwell.com]


Greg Fretwell
akmaster #209869 05/08/13 11:00 PM
Joined: Apr 2002
Posts: 7,274
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akmaster:

"I drive a ground rod run #6 to meter base this is the GEC correct? The GEC is run with circuit conductors"

The 'GEC' terminates at the neutral block in first means of disconnect of the service. Your POCO may allow it to be terminated within the meter base, but that is forbidden here by PSE&G.

The 'ground' with the circuit conductors is "EGC" for Equipment grounding conductor.


John
akmaster #209871 05/09/13 02:20 AM
Joined: Jul 2004
Posts: 9,643
G
Member
We had two policies here from the same PoCo. In Collier County they wanted the GEC in the meter can. In Lee County they wanted it in the service disconnect.
I understand they have now decided the service disconnect is the right place.
The code says
Quote
The grounding electrode conductor connection shall be made at any accessible point from the load end of the service drop or service lateral to and including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.



Greg Fretwell
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