I'am running 2" EMT from an outside enclosure through the exterior wall into a switch room that is being attached with beam clamps, The EMT is carrying a Fiber optic cable feed to the switch room that converts to PVC upon entering the room, can I ground the EMT outside using a ground bushing with a ground rod or does it have to be grounded to the building ground? The EMT is dedicated to the fiber only.

  • What if any mains power wires or cables will be in that conduit also? Even if not you, a 2" conduit will be a tempting route for the next person who needs to get power through. The answer turns on this question. Commented Feb 19, 2019 at 18:18
  • What is the outside enclosure made of, and is it grounded? Commented Feb 20, 2019 at 0:23
  • The enclosure is a metal NEMA 3 outdoor. The enclosure itself is not grounded, but the 2" REMC from the enclosure entering the building has a grounding bushing and is grounded with a #6 bare copper wire on the outdoor enclosure side, from there the conduit run is 80ft to the comm room. Commented Feb 20, 2019 at 13:25

2 Answers 2


You don't need to ground a hamster run, either.

Suppose you had a hamster habitat. And instead of fiber optic, you were using this EMT to extend the hamster habitat to an outdoor maze. Would this habitat run require grounding *solely due to using EMT as a building material? Of course not. That would be silly.

Well, as far as NEC is concerned, fiber-optic cable that has no DC wires running it counts the same as a hamster. It simply does not count for anything at all, and is completely out of its jurisdiction.

The only time fiber-optic cable is in NEC's jurisdiction is when you intermix it in a conduit with electrical wires. But even then, they consider it disregardable if there is nothing metallic in it.

  • Or to put it another way: If you reuse something "not from the electrical world" for electrical, then NEC gets involved. But if you use something "from the electrical world" for something not electrical, the NEC says "have fun". Commented Feb 20, 2019 at 18:29
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    @manassehkatz right. Like EMT is the material of choice for geodesic domes (and by the way, I wrote "material of choice" before I even found that link, so funny synchronicity). Commented Feb 20, 2019 at 18:35

To be code compliant you would ALSO bond the fiber at the service entrance with a intersystem bonding termination. NEC 250.94

Just driving a ground rod and not bonding it to the service supply w/ a intersystem bonding termination creates parallel paths and potential differences for voltages.

Edit: In light of the dielectric properties that some Fiber cables have, NEC 770.93 requires the bonding or grounding electrode of fiber only when in contact with electric light or power conductors. If you do decide to bond even though the fiber is not in contact, there are quite a few requirements. Some that may be relevant to your scenario is the use of non-corrosive material like copper or similar material for the bonding. Galvanized conduit would suffice but not regular EMT.

  • The room that the EMT conduit goes into is actually a comm room and there is no power service supply for grounding entering the room other than the electrical outlets, how would I bond the EMT then if not with a ground rod. Commented Feb 19, 2019 at 21:55
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    Bond the fiber? You realize it’s non-conductive plastic, probably in a non-conductive shell.
    – DoxyLover
    Commented Feb 19, 2019 at 22:42
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    I've been doing some reading and in light of what DoxyLover brought up about the dielectric properties of fiber, the code Article 770.93 would be more prudent to the scenario
    – Kris
    Commented Feb 20, 2019 at 2:12

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