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Replacing a sub panel (with neutral from main panel and local ground rod). The branch circuits will come in via a Wiegmann gutter above the subpanel.

Is there an issue having a grounding bar in the gutter, and terminating all the grounds there?

Intent is just to keep the panel itself neat and tidy by only bringing the lines/neutral into it.

Follow on question - if that is ok, can the grounding conductor (from the rod) just pass through the panel (from below) to the gutter above? Or should it also bond to the panel itself.

Hope that’s clear!

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  • I take it there's an incoming grounding conductor from the main panel as well, or is this a "grandfathered" case where the sub's in a different structure and the feeder can't be upgraded from 3-wire to 4-wire? Dec 28, 2020 at 2:47
  • Different structure with 3-wire feeder, yes. We may in the future be able to upgrade the feeder to 4, but for now it’s stuck at 3.
    – noelep
    Dec 28, 2020 at 3:19
  • I take it that the existing feeder is a direct-buried setup that's impractical to upgrade without retrenching? Dec 28, 2020 at 3:20
  • Yes, correct. One day maybe!
    – noelep
    Dec 28, 2020 at 3:21
  • @ThreePhaseEel - I think I see what you are getting at? With a 3-wire feeder, the subpanel should have its neutral bus bonded to the panel. 250.32(b)(2). Would that preclude terminating the branch circuit grounds outside of the subpanel?
    – noelep
    Dec 28, 2020 at 3:45

1 Answer 1

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The equipment grounding conductors can join together in the gutter...

The overall thrust of your plan, where you bring a bunch of branch circuits into a gutter then send their hots and neutrals to the panel via a short conduit nipple, falls under NEC 250.122(C):

(C) Multiple Circuits. Where a single equipment grounding conductor is run with multiple circuits in the same raceway, cable, or cable tray, it shall be sized for the largest overcurrent device protecting conductors in the raceway, cable, or cable tray. Equipment grounding conductors installed in cable trays shall meet the minimum requirements of 392.10(B)(1)(c).

Since we're dealing with 120/240V branch circuits here, this requirement can trivially be met by using a metal nipple with double locknuts (one inside, one outside) at each end to join the gutter to the loadcenter. Note that since the Wiegmann gutters/troughs do not ship with a grounding terminal bar fitted, you'll have to fit a UL467 listed one yourself. If you have a drill/tap (or combination drilltap) in either 10-32 or 1/4-28 handy, you can drill & tap a couple of appropriately spaced holes then fit a matching bar using suitable machine screws:

  • For the 10-32 case, you'll want to use an Ilsco NBAE series bar of the appropriate size with two mounting holes drilled 2.344" apart and 10-32x1" machine screws to mount the bar to the holes
  • For the 1/4-28 case, you'll want to use an Ilsco NBAS or Penn-Union NA-400 series bar instead, using 1/4-20x3/4" screws (mounting hole spacing varies in this case)

However, not everyone is equipped to tap holes in sheet metal. For those who aren't, an alternative is to use an Ilsco NBAE series bar, but mount it using 10-32x1" thread forming screws (Fastite™ or equivalent type) into #21 pilot holes in the gutter drilled on the same spacing as above.

...but that doesn't extend to the grounding electrode conductor

However, since you have a legacy 3-wire feeder to the outbuilding in question, you must land the grounding electrode conductor on the bonded neutral bar of the outbuilding's subpanel. This is by analogy to a service entrance or separately derived system, since both those points have bonds present and both situations require that the GEC be connected to the neutral (grounded conductor), not to an equipment grounding bar or point. Furthermore, trying to land the GEC in the gutter would most likely violate NEC 250.121, which prohibits the GEC and EGC from sharing the same conductor/wire except under a few select circumstances (which you are not going to run into here).

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  • Perfect - that answers my question. Thank you! For anyone reading this I’m dealing with the implications of a 3w feed over here
    – noelep
    Dec 29, 2020 at 1:55
  • Last time I bought a 10-32 tap at the hardware store, I think the tap was $4 (and came with the #21 drill IIRC) and the tap handle was $5. Tapping is not a terribly hard skill, so I would think any perceived inability is simply unfamiliarity. Dec 29, 2020 at 3:15
  • @Harper-ReinstateMonica -- I'm not sure how manual tapping works for holes bored in sheetmetal (vs. the thick stuff you normally associate with tapped holes) -- apparently that's an application the Greenlee drilltaps are sort of intended for, but I suspect some folks wouldn't be comfortable with that all the same Dec 29, 2020 at 3:20
  • Oh well, maybe I'm off the wall here, but I'm comfortable tapping 10-32 into metal the thickness of typical drawn steel junction boxes. Wouldn't a gutter be thicker? Dec 29, 2020 at 3:40
  • @Harper-ReinstateMonica -- yeah, a gutter would be thicker, so I reckon that drill/tap would be OK Dec 29, 2020 at 3:51

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