Grounding Questions Tram VHF Antenna.

[gradymck]

Couple of buddies came over and helped upgrade my online scanner (railroad) feed here in Western North Carolina that monitors local railroad traffic.

The Tram 1487 VHF antenna is mounted on a piece of metal conduit/bracket (see photo below) and the Coax runs down into the office and into a Kenwood TK-7180 radio (just located inside the far window)

1. I’m going to install a lightning protector between the radio and coax that allows a ground wire to be run outside to a ground rod. Does that satisfy “grounding the antenna”?

Searching online seems to be a rabbit hole of opinions. Just looking for some thoughts from the group.

 

[mmckenna]

1. I’m going to install a lightning protector between the radio and coax that allows a ground wire to be run outside to a ground rod. Does that satisfy “grounding the antenna”?

The purpose of the protector is to give the energy a path to ground before it enters your home. Ideally the protector would be installed where the coax enters the home. Either outside, or just inside.
Installing it at the radio is not the ideal location.

You also want to ground the mast. That should be a heavy gauge copper conductor running from the mast straight down to a ground rod below the antenna. National Electric Code -requires- that the new ground rod be bonded to the existing home ground rod.

Your protector should be connected to the new ground rod, also. You want all the ground equal, no difference in potential.

 

[gradymck]

The purpose of the protector is to give the energy a path to ground before it enters your home. Ideally the protector would be installed where the coax enters the home. Either outside, or just inside.
Installing it at the radio is not the ideal location.

You also want to ground the mast. That should be a heavy gauge copper conductor running from the mast straight down to a ground rod below the antenna. National Electric Code -requires- that the new ground rod be bonded to the existing home ground rod.

Your protector should be connected to the new ground rod, also. You want all the ground equal, no difference in potential.

Appreciate the insight.

So, I need to have an electrician come over and offer advice, or just take the antenna down and mount it back in the attic (where I’m guessing it doesn’t need to be grounded)

 

[WA0CBW]

If you are not comfortable doing it yourself then yes you should call an electrician. Following the NEC rules is for your electrical safety. Putting up an outside invokes additional NEC rules for your safety.
Bill

 

[mmckenna]

Appreciate the insight.

So, I need to have an electrician come over and offer advice,

A good electrician can help you meet National Electric Code requirements. If you are uncomfortable doing this your self, that's a good plan.

or just take the antenna down and mount it back in the attic (where I’m guessing it doesn’t need to be grounded)

Mounting an antenna inside the home may remove the need for NEC compliance, but it doesn't remove the risk. Lightning can still find your antenna through the thin roof sheathing. Plywood/shingles/tar paper won't magically stop lightning.
And direct lightning strikes are not your only risk. Even a nearby lightning strike can induce enough energy into the antenna and feedline to cause damage.

Keep your antenna where it is, and have it properly grounded.

 

[gradymck]

You mentioned the protector ideally should be just outside or just inside where the coax enters the home.

What’s the difference? I would think it would need to be outside regardless? Once it’s in the home weather it’s right where the coax comes in, or 20’ later close to the radio I’d think it wouldn’t make much difference (I.e it’s already inside)

Am I missing something there?

 

[mmckenna]

Am I missing something there?

The purpose of the protector is to get that energy to ground. You want the shortest/straightest path possible. Sharp bends, turns, etc. can result in issues. If it's a direct strike, unlikely all this is going to help much, but the sharp bends can result in that energy jumping off to take a shorter/easier/straighter path to ground. Having it do that inside the home is not what you want. You want that all to happen outside, or very close to outside.

My installs at work have a large copper grounding plate just inside where the coax enters. The entrance protectors are mounted to that within a few inches of entering the building. That copper plate is connected to ground with some large copper conductors.
Then there's usually a short jumper to the equipment.

Goal is to not let that energy into the building or near the equipment/users.

 

[TGuelker]

You mentioned the protector ideally should be just outside or just inside where the coax enters the home.

What’s the difference? I would think it would need to be outside regardless? Once it’s in the home weather it’s right where the coax comes in, or 20’ later close to the radio I’d think it wouldn’t make much difference (I.e it’s already inside)

Am I missing something there?

The arrestor needs to be connected to the house ground rod that is driven into the earth that is on the outside of the house.

If you put the arrestor inside the house, the ground wire would be looped from outside to inside the back out again.

Not to mention the hazard from a strike following the ground wire into the house.

 

[mmckenna]

National Electric code says:

810.20 Antenna Discharge Unit:
(B) Location. The antenna discharge unit must be located outside or inside the building, nearest the point of entrance, but not near combustible material or in a hazardous (classified) location as defined in Article 500.

A good visual guide:

https://www.mikeholt.com/instructor2/img/product/pdf/17LED-1498-sample.pdf