scooterspal wrote:
Hello all.

I need some advice regarding the electrical safety ground for a wifi
antenna I'm installing on the brick wall outside my office building.

Is this in a place where the National Electrical Code applies (or some
similar code)? Are you legally liable if it's done wrong?

If so, the answers to all your questions as to "requirements" are in the
code. I've put some comments in below, but I've specifically avoided
giving you required gauges of conductors, etc., because YOU need to go
read the rules and figure it out.


The antenna is in a 40" x 2" diameter nylon tube.

That's the radome over the antenna. The actual antenna is made of metal
and is inside the radome.

It will be mounted
using a standard A-frame type Channel Master side mount. A short piece
of mast up from the two wall mounts to secure the antenna with U clamps.
It will be up on the wall outside my office door maybe 10 feet.

The mast will need to be connected to the grounding system by an
appropriate sized (as defined in the code) conductor. (in many cases,
the coax shield can serve as the grounding conductor, so you might not
need to run a separate wire)


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.

Which the NEC requires you to connect to the building electrical safety
grounding system in a particular way. (i.e. you can't just casually hook
it up with any old wire to any old place).

The building is on a hill so the AC units are all mounted on concrete
slabs on the ground at either end of the building. There are no antennas
on the roof... only two old vents from when there was a diner upstairs
and the usual vent pipes from the bathrooms. Power comes in from
underground to a central location at one end of the building.

There is most likely a grounding point at the service entrance. That's
where you ultimately need to connect to. You can have other ground
connections too (depending on the situation) but all the grounds have to
be bonded together.


The building is of wood construction with red brick facing. Shingled
A-frame roof like on a house. It is about 100' wide and my office sits
smack in the middle on the lower ground level.

So thats my setup. Now how and where to connect the safety ground is my
concern.

1) Do I simply go straight down into the ground below and will that
create any arching issues with anything else in/on the building?

You can install an appropriate grounding electrode (i.e. rod) and ground
to that, BUT, you need to connect that rod to the building grounding
system with the appropriately sized conductor.

2) Is it better to bring the ground lead into the building and over
to the circuit breaker panel for my office (a distance of about 40') and
attach to the neutral wire at that point?

Under no circumstances should a electrical safety ground ever be
connected to the neutral, except at the one point where the groundING
conductor (aka "greenwire ground") is bonded to the the groundED
conductor (the neutral/white wire). (There are some weird exceptions,
but you're not in any of those situations)

If so, what guage wire for
that distance is required?

Specified in the code. Distance doesn't enter into it.

3) There are probably some large electrical conduits just inside the
wall (that supply power to nextdoor and upstairs) where my AP will be
mounted. Can I attach the ground to one of these with a suitable clamp?

No. While conduit (metallic raceway in code-speak) can serve as the
grounding conductor for branch circuits (e.g. you can ground the third
pin in the receptacle that way), you can't "share" it with other
grounding needs. (and, besides, it's a bad practice for RFI reasons.)

Take a look at the "Low Voltage Handbook" on the Mike Holt website
(http://www.mikeholt.com/) It covers all the grounding and other code
requirements that apply to antennas and the like (including
interconnection of grounds, sizes of conductors, etc.)

Given the high cost of copper these days, you should seriously consider
using aluminum grounding wire. With the correct connectors, it works
great, and it's a lot cheaper and lighter weight.

By the way, there's lots of non-compliant installations of DBS dishes,
WLAN access points, etc. around by, to be frank, hack workers who don't
know or care. Just because the building hasn't burned down yet or no
hardware been damaged or nobody has been killed, doesn't mean that it's
an OK practice.


Thanks for the help.

Good luck. It's not all that hard to do it right.

James Lux, P.E.