Coaxial Surge Suppressor Grounding on Metal Frame Building?

[constantlylearning]

We have a an installation where we have two antennas installed on the roof of a metal frame building. One antenna is a GPS antenna that barely protrudes above the roof line. The other is an electrostatic antenna that protrudes about 6 or 7 feet above the edge of the roof from the side of the building. For various reasons, we have decides to put coaxial surge suppressors on the coaxial cables leading from both antennas going into the building (through conduit).

The problem is that these antennas are a long way from the electrical service entrance grounding point. So running a ground cable across the roof, down the side of the building to the service entrance or to a new ground rod (a distance of at least 100 feet) would probably negate the effectiveness of the surge suppressor.

It occurs to me that I could install the surge suppressors outside the building and then ground the surge suppressors to the metal beams that are the frame of the metal building by running a ground conductor through conduit back into the interior of the building, which would be a distance of about 10 feet. But, I have no idea how the metal framing members are bonded to one another or how the metal frame is tied into the grounding system for the building. (The building was built back in the 70's.)

Or, it might be better to put the surge suppressors inside the building, but I'm still stymied by what I should ground the suppressors to.

To be honest, I think it would be best to have the suppressors outside the building, shunting a surge before it can enter the building. But there is no short path to ground from where on the roof these antenna are located.

The building is a metal-siding building. I'm sure the siding would be an excellent surge path, if it were not painted. But I don't think I can rely on this either.

Any suggestions?

 

[DanEE]

Is there solidly grounded structural steel underneath the metal siding? It may be useable if solidly grounded.. For these types of situations I would suggest NFPA 780 for the best advice or documentation from the Lightning Protection Institude (LPI). . .

If not something you can take on your self, a company that holds certifications by the Lightning Protection Institude (LPI 175) and in NFPA 780 could do the job.

I am currently working on a similar situation in that I have radio repeater systems installed on a university campus building that must be relocated due to a major gut and rebuild of the existing building. The proposed building relocation sites have certified lightning protection systems installed..

In my case, the grounding/bonding work required to relocate the antennas to the new site must be done by a certified installer to maintain certification on the lightning protection system. I am fairly fluent in grounding/bonding as defined by the NEC and in the practices defined by NFPA 780, but do not hold a certification by LPI.. Therefore in my situation, I must sub the grounding/bonding work out to a certified company.. Fortunately the same company that did the original installation and certification of these systems is located nearby, and could do the minor additions and keep the certification valid.

 

[DRWeig]

You might try contacting Ditek with your question, they (as well as DanEE) are very helpful.

http://www.ditekcorp.com

Note: I have no relation to Ditek, but they've been helpful in the past for me.

Best to you,

Goober Dave

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