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#79798 01/25/02 08:18 PM
Joined: Dec 2000
Posts: 4,294
Is it allowable to bring the secondary GEC for a separately derived system (aka xfrmr) through the conduit with the primary feeder and terminate it at the service GEC?
(No problem with capacity, service GEC/Ufer is a 3/0)

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Joined: May 2001
Posts: 717
Electure, 1999 code 250-30, and all others for the 30 years I've been around, the grounding electrode must be as near as practicable to the transformer. If there is NO way to bond it closer I can't off the top of my head find fault (no pun intended) with your method. If there is a way, you would be in violation not to use it, including a ground rod, etc.. I'd have to consider the capacitance of the method, I really don't like, at first blush, it being mixed in with phase conductors of the primary side, too danged much choke for fault purposes for my liking.

Joined: Sep 2001
Posts: 26
Depends on the type transformer and system you are referring to. You can ground the secondary of the transformer at the transformer and run an equipment ground with the conductors feeding the panel or use the neutral (if this is a grounded system) as ground to the panel and ground the panel as you would a service. Using the neutral generated at the transformer as the ground to the panel, is much more practicle.

Joined: Dec 2000
Posts: 4,294
Sorry (again) for a bad explanation.
45 KVA 480X120/240 Delta. It's about 6' from the service. Seems almost silly to run a separate conduit??

Joined: Aug 2001
Posts: 599
I posed this question a couple of weeks ago to the chief electrical inspector for the City of Los Angeles in a grounding class he taught at our shop.

He had a drawing of a typical panel (480/277) feeding a transformer feeding a panel. (120/208). I asked if the 480/277V panel in the diagram was the service equipment, would it be acceptable to run the grounding electrode conductor through the primary conduit with the primary feed to the building grounding electrode system.
Answer: Yes
However, now the primary conduit must meet the same bonding requirements as a GEC in it’s own metal conduit.

You could accomplish that pretty cheap by punching your KO’s and using bonding lock nuts. [Linked Image]

PS: I got the colored MC from Alflex. Now I have every color combonation under the sun. What an invintory nightmare! [Linked Image] It will make for a nice instal when we are done though.

[This message has been edited by Nick (edited 01-25-2002).]

Joined: Aug 2001
Posts: 599
PS again: That would also mean no flex connection on the primary.

Joined: Jan 2001
Posts: 75
I think it is poor practice, but not a violation if installed per 1999 NEC 250-64(e).

Remember, that the bonding bushing (on any type of KO, one hole or concentric ) must be connected to the GEC and not just the enlosurer(s) (boxes).

Joined: Dec 2001
Posts: 270
If the specs allow you to NOT install flex between the panels and the transformer, and if the transformer is not to big and noisy, then I think that would be a really cool way to go, with bond bushings at each end of the conduit nipples, and lay-in lugs in the transformer case for the GEC. Remember, the code allows you to connect your derived panel's GEC right to the ground bus of the service panel [250(a)(3)(c)exc.].

Joined: Oct 2001
Posts: 30
I install a lot of 200 amp 480 volt service for pump stations, with a 5 kva lighting transformer. These do not have structural steel so the nearest avavilable electrode is the building GE system. I'll run from the lighting panel through the raceway and then outside to the ground rods. Ii its a metal enclosure or raceway I bond at both ends, this makes a lot of work and is a good time and materials job.

If possible I'll run straigt outside and use PVC conduit to sleeve it. Sometimes I'll go out through the service disconenct (primary, if you will).

For connections to the lighting transformer, Ilve started using liquid tight non-metallic flex. Then I don't have to bond the flex.

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