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I have an HD antenna mounted to a storage shed, not even as high as the house roof. It's close to where the electrical service enters the house. There's no ground rod in sight. (House built in 1971.) However, electrical is underground, and there's a metal conduit from the meter into the ground.

I'm guessing (!) that the conduit is grounded. My thinking is that, since it goes underground and constitutes a ground itself, it must (by code) be connected to the main ground.

I could pay an electrician a few hundred dollars (or, in my experience, much more) to provide a ground to the antenna, or I could just ground it to the conduit, which has a very handy clamp where it's attached to the brick wall.

Probably 90% of home antenna installations aren't grounded at all, but I thought I'd make an attempt to do it right.

Above grounding would also apply to the ground block which will be attached to the outside wall, near where the coax enters the house.

Tester101
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Marc Rochkind
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2 Answers2

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If the conduit is metalic, and at least size 3/4", and at least 8 ft. long. Then you should be able to use it as the grounding electrode for the antenna.

If the conduit meets all these criteria, then you'll want to bond the antenna mast to it using at least 10 AWG solid copper wire (810.21(H)). You'll have to use a connector designed for the purpose, so you probably can't just tuck the wire into the bracket holding the conduit to the building.

National Electrical Code 2014

Chapter 2 Wiring and Protection

Article 250 Grounding and Bonding

250.52 Grounding Electrodes.

(A) Electrodes Permitted for Grounding.

(5) Rod and Pipe Electrodes. Rod and pipe electrodes shall not be less than 2.44 m (8 ft) in length and shall consist of the following materials.

(a) Grounding electrodes of pipe or conduit shall not be smaller than metric designator 21 (trade size 3/4) and, where of steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.

(b) Grounding electrodes of stainless steel and copper or zinc coated steel shall be at least 15.87 mm (5/8 in.) in diameter, unless listed and not less than 12.70 mm (1/2 in.) in diameter.

Since you're using the conduit as a grounding electrode, you'll have to bond the conduit to the main structures electrical system grounding electrode. This must be done using at least a 6 AWG copper wire (810.21(J)).

You'll also have to ground the coaxial cable, and install an antenna discharge unit at the house. See this answer for more detail.

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Tester101
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  • Thanks! It's metallic, about 2 inches in diameter, and much more than 8 feet long, although what happens below ground in unknowable. So, that's what I will do. – Marc Rochkind Jan 31 '15 at 01:02
  • Thanks for mentioning the separate bracket. I realized after I posted that such specialized connectors were available, to tightly dig into the metal of the conduit. – Marc Rochkind Jan 31 '15 at 01:06
  • @MarcRochkind Before you proceed, you should insure that the conduit is "electrically continuous". You can determine this by testing the continuity (or resistance), from one end of the conduit to the other. – Tester101 Jan 31 '15 at 01:42
  • Two problems, Tester101: I don't have two ends of the conduit. It goes from the meter into the ground and disappears. Second problem is that bonding the conduit to ground requires that I have a ground, which was the original problem, so your answer is circular! To restate the problem: The actual ground is not visible, I don't want to pay an electrician hundreds of dollars, so I want to connect to the conduit under the assumption that it's grounded already. – Marc Rochkind Jan 31 '15 at 01:45
  • Sorry, I thought the conduit you were using was the conduit that the coaxial cable was running through (from shed to house). It sounds like you're going to have to drive a ground rod at the shed, and bond it back to the grounding electrode at the house. The diagrams in the answer I linked to will help you. – Tester101 Jan 31 '15 at 01:55
  • No need for a separate rod, as the shed is about 5 feet from the conduit leading into the house. If I had the main ground, I wouldn't deal with the conduit. That was a shortcut, because I can't find the main ground. Somehow, my original question, in which I said I couldn't find the ground, got transformed into one about how to ground the conduit or to ground a secondary ground rod. – Marc Rochkind Jan 31 '15 at 02:22
  • You can only use the conduit as a grounding electrode, if you bond the conduit to the grounding electrode of the electrical system, or if it already is bonded. there's no shortcuts, if you want to do it right. – Tester101 Jan 31 '15 at 02:26
  • @Tester101 -- if it's the conduit I *think* it is (i.e. the raceway carrying the main service entrance into the meter box), it darn well should be bonded to the grounding electrode of the electrical system -- or could it *be* the grounding electrode of the electrical system? – ThreePhaseEel Jan 31 '15 at 05:06
  • I don't believe our old house had an actual grounding rod. So all houses may not have them. I believe everything in our house was eventually grounded to the plumbing. If your house is an older house, that's maybe why you can't find an actual grounding rod. – DA01 Jan 31 '15 at 16:43
  • @Tester101 -- 250.52(A)(8) allows for "other local metal underground systems or structures" to be used as a grounding electrode -- does a ferrous service-entrance raceway not comply with that? – ThreePhaseEel Jan 31 '15 at 19:49
  • @ThreePhaseEel Sure, but like I said. If that conduit is used, it has to be bonded to the electrical system's grounding electrode (810.21 (j)). – Tester101 Jan 31 '15 at 21:18
  • @Tester101 -- it seems that the conduit or raceway housing an underground service entrance would be bonded to the grounding electrode as a matter of course... – ThreePhaseEel Jan 31 '15 at 23:35
  • @ThreePhaseEel Not necessarily. The conduit may be feeding the meter pan, then the service panel could be fed by a cable or nonmetallic conduit. – Tester101 Feb 01 '15 at 00:16
  • @Tester101 -- aaah, I see your point there -- I was forgetting that the meter pan and breaker panel might not be bonded together at all. – ThreePhaseEel Feb 01 '15 at 00:33
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If the conduit is metal, and penetrates the ground it is, by definition, grounded.

But you can also just go buy a grounding rod at Home Depot as well if you'd prefer to do it that way. It's just a copper rod you pound into the ground and attach a copper ground wire too.

You can also ground it inside via the coax. This is how most satellite dishes are grounded. Inside the house there's a groundable coax coupler. Coax goes in one end and out the other, and then the coupler, itself, is connected to a ground inside the house (typically conduit, plumbing or a ground in a junction box).

All that said, would this be the highest metallic element on your house? If not, I don't know that grounding is really necessary. EDIT: it looks like, upon further digging, all antennas are required to be grounded per code.

DA01
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  • Not only is it not the highest metallic element of the house, but not even of the shed. There's a rotating metal ventilator at the highest point of the shed rod. Regarding your comment about a separate grounding rod: I thought of that, but everything I read says such a secondary rod must be connected to the main ground, which was the original problem to be solved. I don't know why this should be necessary for a separate antenna, as it's as connected to the house electrical system about as much as my neighbor's house is. (Assuming coax is grounded to that same rod as the antenna.) – Marc Rochkind Jan 31 '15 at 01:05
  • If the metallic ventilator on top of the shed is grounded, you may not have to worry about the antennae. I'm not positive about that, though. I've never heard that a secondary ground needs to be connected to the main but that could be true. I'd be interested in knowing why. I still think just grounding it through the COAX coupler will be the easiest solution. – DA01 Jan 31 '15 at 02:05
  • Ventilator is not grounded. – Marc Rochkind Jan 31 '15 at 02:20
  • Regarding "grounding through the COAX coupler": I am NOT asking how to bind things to the primary ground. My problem is that I can't locate the primary ground. I was wondering if I could use the main conduit as a proxy. – Marc Rochkind Jan 31 '15 at 02:25
  • @MarcRochkind gothcha. In theory, the conduit should be grounded. Ideally you'd know where the grounding rod is, but even if you don't--at least in theory--everything in the house should be grounded to it. So if the coupler is grounded to a junction box, for instance, that should be linked back to the main ground. – DA01 Jan 31 '15 at 04:11
  • DA01: Thanks... with all these unknowables, I've decided that your approach is the one that's most appealing. ;-) – Marc Rochkind Jan 31 '15 at 05:17