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.

  • 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 '21 at 19:40
  • 1
    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 '21 at 21:59
  • 1
    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 '21 at 12:31

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.

  • 1
    Grounding retrofits for branch circuits are explicitly permitted by the NEC in 250.130(C). Feeders are rather hazier.... May 6 '21 at 11:40
  • 2
    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 '21 at 17:48

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