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.

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

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.

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.

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?

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

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?

Thanks for the help.

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.

Hello Jim:

I appreciate the detailed reply and I have printed out the Low Voltage
Handbook and will read it over this weekend.

When I started doing research I found this web site for dish
installations. Can you comment on what it describes as the "5
suitable grounding locations". They seem to indicate that you can use
an electrical panel and or the "raceway" as a ground. I'm confused.

http://www.dbsinstall.com/whatis/Whatisgood-5.htm

Also, why is there a mention for separate grounding of the mast
and the coax?

Do I need to provide one ground for the mounting pipe (mast) that
secures the base of the antenna (the aluminum sleeve that contains the
connector at the base) to the brick wall and a second ground to the
grounding lug on the inline gas discharge unit?

Thanks for the help on this. I want to get this right!

scooterspal wrote:
Hello Jim:

I appreciate the detailed reply and I have printed out the Low Voltage
Handbook and will read it over this weekend.

When I started doing research I found this web site for dish
installations. Can you comment on what it describes as the "5
suitable grounding locations". They seem to indicate that you can use
an electrical panel and or the "raceway" as a ground. I'm confused.

http://www.dbsinstall.com/whatis/Whatisgood-5.htm

You're talking about #2 and #3 in the referenced page?

If the panel provides a designated grounding point that's fine.. but
that's the "electrical service panel", not just any old panel in the
system.. it's the one where the service entrance is, and where the
building grounding system is bonded to the earth ground.

Likewise, that picture of the conduit is most likely the service
entrance. As the text says, the "conduit running to the service panel"
or "between sub panels". The conduit running between the main panel and
sub panels is often used as the main grounding conductor, in which case
it would be acceptable.

As far as water pipes go.. in many jurisdictions, the water pipe ground
isn't allowed any more (because of the prevalence of plastic pipes and
various and sundry electrical isolation joints to prevent galvanic
corrosion).

One wants to look at the nice disclaimer at the bottom too.. "your local
codes may vary" and that's the real kicker.. what the code says is sort
of a starting point.. it's your inspector that makes the difference.


Also, why is there a mention for separate grounding of the mast
and the coax?

In many cases, one can't guarantee that the coax can serve as an
appropriate grounding conductor (i.e. it's not big enough, or there are
removable connectors, etc.), so in that case, you need a separate
grounding conductor. (You'll notice that the code requires that the
bonding conductors essentially be permanently attached. hard to do that
with removable connectors, like you usually find on coax)


Do I need to provide one ground for the mounting pipe (mast) that
secures the base of the antenna (the aluminum sleeve that contains the
connector at the base) to the brick wall and a second ground to the
grounding lug on the inline gas discharge unit?

Not necessarily. You can daisy chain to a certain extent, but you
should consider the implications for your overvoltage protection. Too
much running hither and yon will increase the inductance of the
grounding line, and depending on what your equipment is grounded to,
that can actually make things worse. (i.e. if your internal equipment is
grounded to the "green wire ground" in the wall receptacle, and the
transient suppressor is grounded to a different wire following a
different path, then you can have pretty big voltages between the two.)


Thanks for the help on this. I want to get this right!

Jim:

Read the Low Voltage Handbook and more of this now makes complete sense.

My plan is to run a #10 insulated copper wire from the main ground
location in the electrical room at the end of my building out and up and
then horizontally along the outside brick wall at about the height of
the mount for my antenna.

From what you are saying, that single #10 lead can be bonded to the
short (probably 24" or less) piece of mast pipe that runs between the
two 12" wall mounts up to the base of the 40" X 2" wifi antenna AND to
the ground lug on the gas discharge that is screwed into the connector
at the base of the antenna mount (inline to the coax cable).

Do I have this correct?

Actually, there will be only a very short piece of #10 from the mast
to the discharge unit. Does it matter which one I connect to first prior
to looping over to the other?

Jim Lux wrote:

Do I need to provide one ground for the mounting pipe (mast) that
secures the base of the antenna (the aluminum sleeve that contains the
connector at the base) to the brick wall and a second ground to the
grounding lug on the inline gas discharge unit?


Not necessarily. You can daisy chain to a certain extent, but you
should consider the implications for your overvoltage protection. Too
much running hither and yon will increase the inductance of the
grounding line, and depending on what your equipment is grounded to,
that can actually make things worse. (i.e. if your internal equipment is
grounded to the "green wire ground" in the wall receptacle, and the
transient suppressor is grounded to a different wire following a
different path, then you can have pretty big voltages between the two.)

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)