Antenna Ground Options

[BlueDevil]

I have a question regarding antenna grounding options.

I am looking to have a single UHF Repeater Antenna on top of a 4 story building. The antenna will be mounted to the side of a elevated portion of the building/roof which is just about in the middle of the building with a fairly large footprint.

What options exist for grounding the antenna mounting hardware and equipment. I have read through Chapter 8 of the 2014 version of the NEC however it is still unclear to me what options are available.

Almost immediately inside of where the antenna will be mounted in a large networking/electrical room with multiple electrical service panels. The hard line coax will be ran into that room. Would be acceptable to run the ground wire into the one of the service panels?

This is more of a learning experience for me. I will not be the one actually performing the work but would like to know what is acceptable and what is not.

Any constructive thoughts or suggestions? Any educational material I should read?

 

[prcguy]

As a once SBCA certified instructor for satellite dish installers, I will say grounding the antenna to an existing metallic conduit on the roof that has a home run to the buildings electrical box using a maximum of 30ft of 10ga copper wire should satisfy NEC. This would be for electrical safety and not for lightning protection.

It might be legal to run a separate ground wire from the antenna through a building penetration to the electrical panels on a top floor but there may be local rules to follow like running the ground wire inside a metallic conduit for the entire path, etc. The potential problem with doing that is a direct lightning hit to an antenna bonded to an upper floor electrical box could destroy every electrical device in the building.

You really need a professional to survey the job if lightning protection is part of your goal and there is a very good chance that it would be impossible to protect the equipment attached to the antenna from lightning.

BTW, what is the guy doing in the bottom picture at the ladder? Making a puddle?
prcguy

 

[jim202]

Is there any steel structural beams any place close to where the antenna is? This is where the NEC will point you to ground a telecommunications antenna on a multi story building. Lacking that, you only other choice is to run a minimum #2 ground wire from the roof down to earth on the outside of the building. Then create your ground system there at ground level.

I don't have a copy of the NEC handy to quote, but I know it's not a good practice to try to use the electrical system for your antenna ground. The first strike on that antenna will clean out any panel there and who knows what other damage it will cause else where in the building.

When I was involved with installing cellular systems in buildings, the electrical inspector always looked for how we grounded the antenna system. He would shut the job down if he even found our antenna ground wire any where near an electrical panel.

 

[mmckenna]

For a lightning ground, you wouldn't want to run to an electric panel. Ideally you'd use building steel.
Like Jim, I don't have the NEC in front of me, but I know what's been done at different installations.

You should ground your equipment to the ground buss that should be in the electric room.

 

[Rred]

Your municipal building code office may be able to tell you what they would want. And that should also keep any insurers happy. Building code also normally keeps any fire department folks happy. There are also sometimes regulations about "things" on the roof, because firemen need clear access without the risk of wires and hazards if they are up there trying to vent it during a fire. So, I'd start with the building code department.