ECN Forum Forums Code Related Discussion NEC & other Code issues GEC ferrous conduit bonding

My question actually concerns a telecommunications bonding backbone (TBB) and/or the branch(es) that land on telecom equipment. However, the way it is handled per ANSI/TUA/EIA-607, the TBB is similar to the GEC on the way it is dealt with in the NEC. Both ends of a ferrous conduit must be bonded to avoid the potential of a choking effect. I will give sinarios followed by my opinion.

1) GEC exits the side of a main service panel, through a chase nipple (or Romex connector), and lands on a steel beam next to the service. No bond bushing/wedge is required.

2) GEC exits the bottom of the main service, through a chase nipple, directly into a steel gutter/trough mounted to the panel. It then continues through another chase nipple before making its way outside to a ground rod. A gutter/trough is not defined as a conduit but does it essentially act as one with the cover on? I still say, no bond bushing/wedge(s) is/are needed.

3) Take the #2 sinario, but instead of using a chase nipple, cut out the bottom of the main panel (leaving just a 3/4" flange around the outside) and bolt it directly to the top of the gutter with a matching hole. The panel and gutter are now, essentially, the same, oddly-shaped box. If #1 did not require a bond bushing then #3 definitely does not either.

4) Again, take sinario #2 but gradually increase the length of the conduit connecting the panel and the gutter. Go from a chase, to a close, to a short nipple (and beyond). At what point is/are bond bushings needed? Also, is the length of gutter ever a determining factor? Since my question actually is for a TBB (and its branches) not a GEC, the ANSI/TIA/EIA-607 rule is that the ferrous "conduit" cannot be longer than 3' without requiring bond bushings. Do I count the total length of wire from where it exits the panel to where it exits the steel gutter in 1, 2, and 4 above?

I understand that IT equipment is typically bonded by a #6 landed on the OUTSIDE of the cabinet, but the layout of the room may make this less than a clean install. Thanks for reading this far.

Note that NEC 250.64(E)(1) addresses grounding electrode conductors in enclosures and general ferrous raceways (not just conduit).

More to the point, the installation - at least in my opinion – should be focused on performance and not semantics about what is or isn’t a conduit or an odd shaped box. The intent of the NEC and the 607 standard is to avoid reducing the effectiveness of the grounding conductor when in proximity to ferrous metal. In that case I would say that you should bond the conductor at each end (or end of chain as the case might be).

A related bonding/grounding standard, ANSI/BICSI N3-2020, clarifies an ambiguity in the ANSI/TIA 607 standard by adding the following regarding multiple short sections in series (less than 3’ each) of ferrous conduit:

“Where multiple short sections are placed in series for the conductor run, they shall also be bonded at both ends as their collective length would exceed the 0.9 m (3 ft) criteria.”

Thank you for the reply.
1) Would you put a bond bushing on a Romex connector in the side of a main panel if it surrounded a GEC? This is a bushing/clamp, not a raceway and I don't see a "choking hazard" (so to speak).
2) Since the gutter is the raceway (not the chase nipple which is merely acting as a bushing) would you install a ground lug near where the GEC exits the gutter? To ensure a parallel run, I assume the GEC itself would need to run through this lug.
3) Your answer fir #1 would apply here.
4) At least as a minimum standard, it appears you agree with me here.

Keep in mind that an AHJ inspecting your installation will use his interpretation of the NEC, and citing telecom standards for why you did or didn’t need to do something might be an uphill battle.

1) With the GEC (TBC for telecom) only entering a ferrous metal enclosure and otherwise running without raceway, I don’t see where Code (AHJ dependent) or Standards would require anything (or if there is even a performance risk). Probably no one will care what you do (within reason and otherwise within Code). If the GEC (TBC) had both entered and exited a ferrous metal enclosure (passthru) I’d say yes that requires bonding to the enclosure at entrance and exit locations with a connection method complying with 250.92(B)(2) thru (B)(4).

2) From a telecom perspective, I’d say this is an example of chaining ferrous components (per ANSI/BICSI N3-2020), and if the longest path is less than 3’ you’re not required to bond the components and TBC at each end of the chain. (Even though the ANSI/TIA 607 standard only refers to conduit, the intent is broader than that and should be thought of as covering various raceways. In any case, there could be a performance issue if length is ignored.)

3) Same answer as #2.

A correction: 2) and 3) aren't chained scenarios, but the 3' maximum is still the deciding factor. 4) is the chained scenario.

I think the normal"bite" of standard lock rings meets the intent of bonding GEC raceways if they are made up tight. I think the stamped ones with sharp teeth work better than the cast zinc ones tho.