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Hypothetical question. I won't self-answer. The purpose is to inform potential answers on another person's question.

Suppose I have a shed with a 200A subpanel, with 3-wire feed that was installed prior to 1999, so it was grandfathered. I now want or need to retrofit ground to that shed. I lay either

  • Rigid metal conduit, which is the ground path, so it contains no wires at all. OR
  • PVC conduit and I install a #2Al ground wire and nothing else.

As such there are no live conductors therein, just EGC (Equipment Ground Conductor). Can I put ethernet or other copper data cables in that pipe? Best answers will include Code cites.

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  • Interesting question, +1. I'd think the first one at least must be okay, because properly bonded rigid conduit is always a ground path that will carry some portion of current in the event of a fault, even if there's a four-wire feed as well. But I'm curious to see the code cites.
    – Nate S.
    Jan 14, 2021 at 19:40
  • 3
    Am curious about the code cites too but since I could install an extra PVC in the trench faster than I could find the code cites, that's what I'd do. :-)
    – JACK
    Jan 14, 2021 at 21:59
  • 2
    My concern would be what would happen to my delicate electronics should there be a ground fault and their cabling is suddenly surrounded by all that voltage flowing through the ground "wire".
    – FreeMan
    May 6, 2021 at 12:31
  • Can you run an EGC separate from its conductors in the first place? Option #3 : you drive a ground rod? Presumably we can ignore the fact that it's conduit : can you run low voltage next to a line voltage EGC? I'd assume as it counts as a conductor, then no. But really the only problem is that by "low voltage" we mean it has insulation not rated to 600v? If it does then you can do w/e you want? (provided it's less than 150v to ground)
    – Mazura
    Oct 15, 2022 at 17:09
  • 300.20 Induced Currents in Ferrous Metal Enclosures or Ferrous Metal Raceways. Exception No. 1: Equipment grounding conductors for certain existing installations shall be permitted to be installed separate from their associated circuit conductors where run in accordance with the provisions of 250.130(C).
    – Mazura
    Oct 15, 2022 at 20:57

2 Answers 2

1

Here is some info for you to digest…

NEC (2017) 840.49 addresses metallic entrance conduit grounding for premises-powered broadband communication systems, including twisted pair:

Metallic conduit containing communications entrance wire or cable shall be connected by a bonding conductor or grounding electrode conductor to a grounding electrode in accordance with 800.100(B).

800.100(B) is lengthy and lays out a lot of requirements, but the key bits are that the GEC for your conduit must be 14 AWG or larger, as short/straight as possible and less than 20 feet, and connected to some part of the existing GEC system, generally.

800.48 is also relevant. If your cable is unlisted, you are limited to a 50 foot span once inside a building but may extend inside using IMC or RMC.

800.48 Unlisted Cables Entering Buildings. Unlisted outside plant communications cables shall be permitted to be installed in building spaces other than risers, ducts used for environmental air, plenums used for environmental air, and other spaces used for environmental air, where the length of the cable within the building, measured from its point of entrance, does not exceed 15 m (50 ft) and the cable enters the building from the outside and is terminated in an enclosure or on a listed primary protector. The point of entrance shall be permitted to be extended from the penetration of the external wall or floor slab by continuously enclosing the entrance cables in rigid metal conduit (RMC) or intermediate metal conduit (IMC) to the point of emergence.

Informational Note No. 1: Splice cases or terminal boxes, both metallic and plastic types, are typically used as enclosures for splicing or terminating telephone cables.

Informational Note No. 2: This section limits the length of unlisted outside plant cable to 15 m (50 ft), while 800.90(B) requires that the primary protector be located as close as practicable to the point at which the cable enters the building. Therefore, in installations requiring a primary protector, the outside plant cable may not be permitted to extend 15 m (50 ft) into the building if it is practicable to place the primary protector closer than 15 m (50 ft) to the point of entrance.

BUT FROM YOUR ORIGINAL QUESTION!!! I hope this was a joke…

“Rigid metal conduit, which is the ground path, so it contains no wires at all.”

Do not do that!!!!!!!!!!

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  • 1
  • It appears that you were actually quoting 800.48, so I fixed it up to use quote formatting to indicate that. Please edit to undo or adjust the quote formatting if I got it wrong. Also, please expand on your "do not do that" admonition. That's a strong statement and needs some explanation.
    – FreeMan
    Oct 17, 2022 at 11:46
  • From the perspective of the data cable installer, you follow these bits of code and your cables and building are suitably protected from all manner of undesirable voltages and currents, including ground faults from sheds like OP's. From the perspective of the shed installer, could you intentionally utilize an existing data conduit, one that does already conform to the code sections noted in this answer, as your ground path? It's not obvious this answer addresses that question. If the pipe is correctly protected from your planned configuration, does that make the plan correct?
    – jay613
    Oct 17, 2022 at 15:17
-3

What do you mean by “retrofit ground?” This phrase makes no sense to me.

If you have a 3 wire feeder (L1, L2 and a “grounded” conductor, aka a neutral) you dont have a ground at the shed and one must be established using one of the approved methods found in article 250 of NFPA 70 (assuming you’re in the USA). You reference 1999, which is a NEC code cycle year in which 3 wire feeders were probably permitted.

If you have a 3 wire feeder to the shed you would have had to install... ground rods or a UFER etc.. The neutral and ground bus bars in the panel would have to be bonded together and you would be establishing a new ground at the shed.

With a feeder, it is required in NFPA 70 that the grounding conductor/ ground wire be ran/routed with the ungrounded and grounded conductors. See Articles 250.24(c) or 250.118 or 250.186(A) and/or 300.3(b) of the NEC.

You cannot just throw a ridged metal conduit in the ground and bond it between your source and your shed and now say its grounded. The ground path must be routed with the current carrying conductors and be installed in a very particular manner.

Your second idea about using PVC with a number 2Al also doesn’t meet the requirement that the conductors all be routed together.

If you install a second conductor between the source and the shed. This second conductor needs to be treated differently from the grounded (neutral) conductor because it isn’t a current carrying conductor (it isn’t meant to carry the unbalance neutral current, its purpose is to facilitate the operation of the over current protection device (breaker) at the source.

Bottom line: if you want to “retrofit” your ground you will need to pull a ground”ing” wire in the same raceway/pathway as the other 3 current carrying conductors. You will need to separate the grounds and neutrals at the shed so that you dont have parallel paths to ground. And deal appropriately with any and all parallel metal paths between the source and the shed.

Again, check article 250 for requirements on grounding and article 230 for feeder requirements.

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  • 3
    Grounding retrofits for branch circuits are explicitly permitted by the NEC in 250.130(C). Feeders are rather hazier.... May 6, 2021 at 11:40
  • 3
    I agree, this answer was written unaware of the retrofit ground rules. Generally a bad idea to open with "I don't understand the keystone term used in the question"... May 6, 2021 at 17:48
  • Retrofit ground: see NEC 2014 250.130(c) and following code updates.
    – Ecnerwal
    Mar 6, 2022 at 23:02

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