Lightning Protection for Lead In Antenna Conductors

[DSoto]

I'm trying to put together a design specification for a cellular signal amplifier to be placed in a home. The product contains an exterior antenna that is not grounded, and a lead in conductor goes into the building to an amplifier that is then connected to an indoor antenna. The installation instructions show no grounded surge protection for the lead in conductors. The question was raised -considering what Article 810.20 of the NEC says- if the NEC REQUIRES installation of a grounded lightning arrester or metal shield from the lead in that is grounded. If the code doesn't require it because the antennas are stand alone and therefore not grounded, and because there is no intrusion into the electrical wiring pathways of the home, we would rather not ground it or provide a path to ground because that would seem to increase the likelyhood of a lightning strike on the device, and also because of the reason below that came from the maker of the system.

"We have never tested the amplifiers to see if using a N connector with a grounding lug will change or effect the performance of the amplifier. We keep the path to the amplifier as clean as possible. We have to worry about external radiated signal as these units have passed both FCC and IC testing. Any other external connection could provide additional radiating paths for the signal which would void our FCC and IC grants.

Somewhere, somebody has to realize that the in building amplifier has an outside antenna, an inside antenna, and the amplifier case. There is no connection of any other type, to the CATV system in a building, electrical system, etc. The only connection we have is from a wall power supply that has a UL rating on it. This power supply converts 120 VAC to 12 VDC to enter the amplifiers independent power supply.

If lightning hits the external antenna, it will most likely destroy the in building amplifier. the AC power supply has internal fuse protection, but would probably be destroyed as well. There are no other connections to any other type of equipment.

I suggested a GFI outlet be mandatory for the amplifier as this would give you shorting and lightning protection to the system, be simple, and everybody can easily get one."​

Does anyone if we are REQUIRED by the NEC to provide the lightning protection described above?

 

[77401]

The best thing I have found is whats called a lighting Preventer. Yes Lighting can't hit this!!

I carry one in my golf bag just in case I'm caught in a lightning storm. I just hold it up hight in the air & finish my round.
It is a #2 Iron, God can't even hit a 2 Iron!

 

[stevearne]

- Not an Instructor topic

- Not an Instructor topic

This post does not fall under Electrical Instructor topics, so I will move it to a Low Voltage and limited energy thread. Please feel free to continue the discussion there.

 

[tom baker]

Yes I do know. If you are installing a system that falls under the scope of Art 810, then the antenna mast must be bonded to the building electrical grounding system. If the antenna is inside the building, then there is no exposure to lighting and the bonding is not required.
If the antenna uses coax, then Art 810 directs you to Art 820. And Art 820 requires a lighting arrestor, nearest the point of entrance of the coax into the building, bonded to the building electrical grounding system.
There are millions of unbonded antenna in the US. The only antennas I see that are correctly installed are commerical cell sites. I have been installing radio systems for SCADA communications and had to get my arms around Art 810 and 820.
Bond everything together and to the building electrical grounding system to create a single point ground.
What I see happening is computer techs are starting to install wireless networks. Most of the time the installation will be not per the NEC. Another common mistake is running the same coax inside as used outside. Inside coax must be a listed coax - flame retardant.
I can say this as in real life I am an electronics technican, and work with a lot of ETs. But I also am a master electrican...

 

[hbiss]

In my opinion bonding the mast and bonding the shield of the coax where it enters the stucture is all you have to do to be code complient. I realize this isn't RG-6 with F connectors but there are many ground block type devices that utilize the connectors you have. Point here is that it is not necessary to use anything more than a ground block that bonds the shield, devices with surge protection on the center conductor are what the manufacturer advised against.

You are all wet regarding the GFI. Its absolutely not going to provide any lightning protection or overload protection. All it may do is nuisance trip and be a general PITA. No reason for it.

-Hal

 

[BarryO]

And Art 820 requires a lighting arrestor, nearest the point of entrance of the coax into the building, bonded to the building electrical grounding system..

A lightning arrestor is not required for coax, AFAIK. 820.93 merely requires the shield to be grounded. Arrestors are required in 810 for twin-lead and other types of unshielded lead-in conductors.

 

[BarryO]

I'm trying to put together a design specification for a cellular signal amplifier to be placed in a home. The product contains an exterior antenna that is not grounded

There's no NEC requirement for antennas to be grounded, only the antenna mast (which also grounds conductive items connected to the mast, such as the boom on log-periodic and Yagi-type antennas, and the reflector on parabolic dish antennas). Grounding the active elements of an antenna would render it inoperative!

The installation instructions show no grounded surge protection for the lead in conductors. The question was raised -considering what Article 810.20 of the NEC says- if the NEC REQUIRES installation of a grounded lightning arrester or metal shield from the lead in that is grounded.

NEC requires the outer conductive shield to be grounded where it enters the building. This should have no effect on performance It should be possible to do this with N connectors, with the use of suitable harware.

we would rather not ground it or provide a path to ground because that would seem to increase the likelyhood of a lightning strike on the device,

It seems to be an old wive's tale that providing an intentional path to ground will increase the likelihood of a lightning strike. First off, studies have shown that towers/structures need to be at least 100m tall to "trigger" lightning strikes. As for "attracting" a strike that would happen anyway, the antenna mast will be at approximiately the same voltage potential with respect to the overhead cloud whether or not it is intentionally grounded.