Can I use a *ground wire only* conduit for copper data cables?

Question

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.

Answer 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!!!!!!!!!!

Answer 2

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.