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At my home I have a detached garage which has sorely needed to have its single branch circuit upgraded to a proper underground feeder, subpanel, the whole works. I didn't want the grounding electrode conductors out flapping in the breeze and thought it would look nice and be better protected too if I run them through EMT down to the soil. That's where I ran afoul of NEC 250.64(E)(1). I need some help figuring out how to do it right.

The code states "Ferrous metal raceways and enclosures for grounding electrode conductors shall be electrically continuous from the point of attachment to cabinets or equipment to the grounding electrode and shall be securely fastened to the ground clamp or fitting. Ferrous metal raceways and enclosures shall be bonded at each end of the raceway or enclosure to the grounding electrode or grounding electrode conductor to create an electrically parallel path." Now, I could just use PVC instead of ferrous and avoid all this, but that wouldn't look nice next to the shiny new RMC risers!

main panel

Here at the main panel I had enclosed the GECs in EMT conduit but had to remove it and leave the GECs exposed to partly-pass inspection and get utility power re-connected. There are two GEC because I installed two ground rods with a separate wire to each. At point A there's a 3/4" knockout so I believe I can use a set-screw connector and a lock nut to bond an EMT to the panel. Is that sufficient? The other end of the conduit, where GECs would exit at point B, must also be bonded to the GEC. Can I bond to just one of the GECs, or must bond to both? (Maybe I should eliminate one of them.) What is the name of the bonding connector I'd use at B?

LB fittings subpanel

The other end is much more complicated. Conduit comes out of the ground, LB and a conduit stub to get through the wall to a 10x10x4 box, then 2" EMT rising up to the subpanel. At point C in the subpanel I need an insulated grounding bushing because there's an eccentric knockout which impairs the conduit bond to the panel. Does the GEC have to be connected to the bushing, or can I just install a #6 jumper wire from bushing to ground bar in the panel?

At D the EMT connector goes into a (slightly oversized) hole cut in the box; does that qualify as bonded? At E there's a set screw connector in a right-size hole. Is that sufficient? Then there's F, the LB fitting. How does the LB get bonded? (Actually.. it is probably be non-ferrous, so maybe it is exempt). Finally at G I'll need the same connector as at B.

Switching to PVC would be so much easier, but.. if there's a reasonable way of getting it done to meet code with metal raceway I'd like to attempt it. That LB is in full sun and a PVC LB would start looking awful real quick.

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  • I take it the GECs in question are all #6, right? Also, is converting the existing setup to use a "daisy chain" of grounding electrodes instead of having two independent GECs an option? – ThreePhaseEel Dec 18 '20 at 2:35
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Your problem: neither the Code nor electrical-fitting-makers ever envisioned someone stuffing two grounding electrode conductors down the same ferrous conduit

You are correct that using ferrous conduit and conduit bodies here would require you to conform with NEC 250.64(E):

(E) Raceways and Enclosures for Grounding Electrode Conductors.

(1) General. Ferrous metal raceways and enclosures for grounding electrode conductors shall be electrically continuous from the point of attachment to cabinets or equipment to the grounding electrode and shall be securely fastened to the ground clamp or fitting. Ferrous metal raceways and enclosures shall be bonded at each end of the raceway or enclosure to the grounding electrode or grounding electrode conductor to create an electrically parallel path. Nonferrous metal raceways and enclosures shall not be required to be electrically continuous.

(2) Methods. Bonding shall be in compliance with 250.92(B) and ensured by one of the methods in 250.92(B)(2) through (B)(4).

(3) Size. The bonding jumper for a grounding electrode conductor raceway or cable armor shall be the same size as, or larger than, the enclosed grounding electrode conductor.

(4) Wiring Methods. If a raceway is used as protection for a grounding electrode conductor, the installation shall comply with the requirements of the appropriate raceway article.

However, the NEC doesn't speak here to what to do in your situation where you have two grounding electrode conductors in the same piece of ferrous conduit. Normally, for a single GEC in a conduit, you can use a lug-equipped grounding/bonding locknut (Bridgeport 162-G or equivalent for 3/4") on the box entrances and a grounding hub fitting (Bridgeport MCH-075) or a hub clamp (Bridgeport 1325-B or equivalent) on the grounding electrode end of the conduit. However, all of the aforementioned fittings are only rated to accept a single wire, and you have two wires. As a result of that, we'll need to find an alternative approach.

Jumpering and tapping our way to success

The good news, though, is we still can use grounding/bonding locknuts with lugs to accomplish the job of bonding the enclosure knockouts as before; however, we need to jumper from said lugs to the grounding electrode conductor itself, not to a grounding or neutral bar in the enclosure. This will require 6 AWG copper (or whatever size your existing GECs are) for the jumper, as well as 6AWG to 6AWG lay-in parallel mechanical taps (Ilsco GTA-2-2 or equivalent) to connect each end of the jumper to a GEC, in addition to the aforementioned grounding/bonding locknuts (which come in various sizes, just make sure to get ones that have lay-in lugs on them). In this situation, the bonding jumper extends from one tap connector, through the lay-in lug on the grounding/bonding locknut, then to the other tap connector on the other grounding electrode conductor, thus connecting both GECs to the raceway bonding point.

At the exit points, though, we'll need to take a somewhat different approach. The aformentioned tap connectors are dual-rated Al9Cu, so using them near the ground is a bad idea for corrosion reasons, and there aren't any equivalent direct burial products out there. So, I'd use an extra grounding clamp on each ground rod, with a jumper from one extra rod grounding clamp, through a lay-in pipe grounding clamp rated for direct burial (T&B JDLI or equivalent) that is fitted on the conduit to bond it, and on to the other extra rod grounding clamp. This works because 250.64(E)(1) lets us land these bonding jumpers directly on grounding electrodes at the grounding-electrode end of the raceway, instead of landing them on GECs.

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