scooterspal wrote in news:kqWHh.8733$jx3.6472
@newssvr25.news.prodigy.net:

....
I have a gas discharge unit that comes with the antenna. It mates to
the
bottom connector and terms with the connector for the 4' of coax wire
that leads through the wall to the wireless AP unit. There is a ground
lug on the side of the discharge unit to attach a lead to.
....

Effective lightning protection is not trivial. It starts with an
assessment of the risk, including whether or not your structure is
effectively protected by nearby structures. The design of a protection
system should be an integated design, what you do to your antenna may
impact the other antennas / conductors / structures that are co-located.

Keep in mind that protection conductors may need to withstand typically
20,000A for 0.1s. The coax outer will probably not withstand that, so you
must route the discharge to ground a different way.

The gas discharge unit is to limit the voltage rise on the inner
conductor of the coax wrt the outer conductor. I think that it would be
unusual that a gas discharge device would be effective unless / until the
antenna / feedline was damaged, due to device's slow ionisation time and
the rather small voltage with fast rise times that would be induced in a
narrow band 2.4GHz antenna. It seems to me that your principle hazard is
the current that will flow on the outer of the coax as a result of a
direct or nearby strike, or the potential difference between your coax
outer and the building earth system in the event of of a direct or nearby
strike.

I know they sell these protection devices for the purpose, but I do
wonder about their effectiveness.

Routing the discharge current effectively to ground is important, but
equipotential bonding to avoid potential differences at critical
interfaces is an important part of solution design.

So the first stage of the solution is to prevent most of the discharge
current following the coax into the equipment room.

I agree with all that Jim Lux has offered you.

Owen

Owen Duffy wrote:
scooterspal wrote in news:kqWHh.8733$jx3.6472
@newssvr25.news.prodigy.net:

...

I have a gas discharge unit that comes with the antenna. It mates to

the

bottom connector and terms with the connector for the 4' of coax wire
that leads through the wall to the wireless AP unit. There is a ground
lug on the side of the discharge unit to attach a lead to.

...

Effective lightning protection is not trivial. It starts with an
assessment of the risk, including whether or not your structure is
effectively protected by nearby structures. The design of a protection
system should be an integated design, what you do to your antenna may
impact the other antennas / conductors / structures that are co-located.

And, decide what exactly you're protecting against. Keeping the
building from catching fire is a very different goal than keeping your
AP alive.

Keep in mind that protection conductors may need to withstand typically
20,000A for 0.1s. The coax outer will probably not withstand that, so you
must route the discharge to ground a different way.

The usual NEC grounding is not designed to address actual direct hit
currents from lightning. It's more to deal with things like inadvertent
contact with an overhead power line, a short from power line to
something metal and then to your antenna, and, to a certain degree, to
induced voltages from nearby strokes.

The focus of NEC is "personnel safety" followed by "structure safety",
with "equipment preservation" being a very, very far distant third.
Likewise, the local regulatory regime is more concerned about you
getting hurt or starting your house on fire than whether your AP
survives. If you're interested in "equipment preservation" there's a
whole 'nother set of places to look for recommendations (the IEEE
Emerald book, IEEE-std-1100 is a good place to start, but pricey to buy.
Roland Standler's book on protecting electronics from overvoltage from
Dover press for $20 is another).

There are also various and sundry books and app notes from the sellers
of protection equipment. They provide valuable information, and
practical applications engineering data, but you DO need to bear in mind
that they reflect that company's opinion of what the best way is. And
that way generally uses their particular devices. (not of some money
grubbing crassness, but because they have analyzed the problem, figured
out a solution, and make the parts for that solution)