RadioBanter - Antenna mast grounding question

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Antenna mast grounding question

Mike,
Putting the mast grounding aside for a minute, I think I'd
have a talk with whoever supplies your electrical power about
the ground that should be there and isn't.
'Doc

On 27 Nov 2003 17:02:33 GMT, Mike Ekholm wrote:

I will be puting a intenna mast up on the roof, and I plan on
running a wire from the mast to a grounding rod. My house is grounded
via just the water pipe, as far as I can tell, no grounding rod connects
to my electrial service. Do I need to run a wire from the grounding rod
to my water pipe to prevent a grounding loop?

Based on my personal experience:

I would verify that you don't have a electrical system ground. If you
don't, then add one post haste. The number, size, and spacing vary
according to soil conditions and the size of your electrical service.
It's for your own safety. The water pipes/system should be considered
as a safety backup.

" Check the electrical codes for your area", or get to know an
electrician. Here the code required I have two, 8' ground rods six
feet apart connected with #6 wire for the electrical service for
*both* the house and the shop. Although fed from the same transformer
they have their own meters and breakers. The TV mast and small
satellite dish required their own 8' ground rod and only a #10 wire
for grounding. BTW we are also required to tie the electrical service
ground to gas pipes and water pipes. Which in our case is strange as
the water system is all plastic except for the water meter.

What size wire should I use from the mast to the rod? and from the rod
to the water pipe, if it is required?

You didn't say what type of soil you have in your area, but most
would be using bare, solid (or stranded), #6 or #8. As I noted above,
the TV antenna mast and satellite dish use only a #10. I use #2 and
have everything tied together for the ham station, but I have a large
antenna system that gets struck by lightening fairly often.

You'll have to fix the return add due to dumb virus checkers, not spam
Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair?)
www.rogerhalstead.com

Thanks!

-Mike Ekholm

I will be puting a intenna mast up on the roof, and I plan on
running a wire from the mast to a grounding rod. My house is grounded
via just the water pipe, as far as I can tell, no grounding rod connects
to my electrial service. Do I need to run a wire from the grounding rod
to my water pipe to prevent a grounding loop?

No, Earth ground is earth ground is earth ground,

That's true, _if_ you happen to be living on a solid sheet of copper,
or a superconductor.

The actual DC resistance of "earth ground" across the width of a house
can be quite substantial. This can lead to a significant voltage
potential developing across "ground" under certain circumstances.

For this reason, the U.S. National Electric Code states that each
building may have only a single "grounding system". If you have two
or more ground points (ground rods, grounded water pipes, etc.) the
NEC says that you must "bond" them together with heavy-gauge wire,
precisely to overcome this resistance. 8-gauge is usually required,
and I believe that some municipalities require even heavier wire such
as 6-gauge.

If you don't do this, then under certain circumstances, an electrical
fault can have some very unfortunate effect. Let's say you have a
grounded antenna mast, with its own ground rod, but that you haven't
bonded it to your electrical service-panel ground. Let's also assume
that:

- You've got a DC-grounded antenna (e.g. a copper-pipe J-pole)
attached to the mast

- Your rig is plugged into an outlet, whose ground wire happens to
come loose, and

- Your rig develops an internal hot-to-chassis electrical short.

At this point, you're probably going to be in a world of hurt. The
"hot" current is going to flow into the rig's chassis, through the
coax braid to the antenna, down the mast to the ground rod, and
through the soil to the service panel. The soil resistance is going
to have two very bad effects:

- It can limit the current flow through ground to below the circuit
breaker's trip limit.

- It'll allow the rig chassis, and the antenna and mast, to remain at
a fairly high voltage above neutral.

As a result, you can end up with both a shock hazard, and a risk of
severe heating and fire. 10 amps through your coax could spoil your
whole day.

You only need to ground the antenna to the grounding rod, the water
pipe and antenna ground rod are both on the same circuit. Just think
of the earth ground as a very large negative terminal on a car
battery.

Nope. The two ground points could very well have tens to hundreds of
ohms of soil resistance between them. For purposes of electrical
safety, bond 'em together!

As Bob Pease of National Semiconductor said (in a different context,
also having to do with ground impedance): "You may be able to trust
your friends. If you're very fortunate, you may be able to trust your
government. You cannot trust your ground."

I'd strongly encourage the OP to check the his local electrical
codes to find out what the ground-bonding requirements are in his
area.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

As Bob Pease of National Semiconductor said (in a different context,
also having to do with ground impedance): "You may be able to trust
your friends. If you're very fortunate, you may be able to trust your
government. You cannot trust your ground."

A very smart guy.

My rule for current: "Always put it back where you got it from."
If you let it find it's own way home, it will usually make a mess.

On 27 Nov 2003 17:02:33 GMT, Mike Ekholm just had to say:
: I will be puting a intenna mast up on the roof, and I plan on
: running a wire from the mast to a grounding rod. My house is grounded
: via just the water pipe, as far as I can tell, no grounding rod connects
: to my electrial service. Do I need to run a wire from the grounding rod
: to my water pipe to prevent a grounding loop?

Thanks for the responses folks. I will run 10ga from the mast to the ground
rod, and I will also run a wire from my house ground system to the ground rod
to prevent a ground loop. I will need to do some code reading to find
what size wire I need to run from the house gound system to the rod.

Thanks!

-Mike Ekholm
--
Mike Ekholm, UNIX Sys Admin -
web: http://www.ekholm.org ham: kc0mpu irc: Nalez
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
UNIX - The Swiss army knife of software.

Nope. The two ground points could very well have tens to hundreds of
ohms of soil resistance between them. For purposes of electrical
safety, bond 'em together!

They are bonded together by earth ground.

The National Electric Code says otherwise. Earth ground is *not*
considered adequate bonding for the purposes of electrical safety.

The antenna is not going to
carry any AC load if your station is grounded. Who knows maybe a 747
will clip the guys antenna at the same time as lightening hits the 747
knocking the ground wire from the antenna and creating a huge fireball
above his house.

The whole purpose of proper electrical *safety* grounding is to ensure
that when things go wrong (short circuits, open neutrals, etc.), they
go as *little* wrong as possible.

Failing to bond ground rods together would be one of those things
which would make no difference *normally* (in the absense of faults in
the building wiring). If a wiring fault, short circuit, etc. were to
occur, proper ground-rod bonding could make the difference between a
tripped circuit breaker (if you're run a heavy-gauge bonding wire),
and a burned-down building (if you didn't bond 'em, and the current
flow through the soil wasn't enough to trip the breaker).

The bonding rule is there for a very good reason... safety.

As a very practical matter: if you fail to follow the Electrical Code
(or your own local rules, if different), then your home may fail
inspection if you try to sell it, and (if a fire occurs) your
insurance company may refuse to pay your claims if they find a
not-to-code electrical installation/modification.

Bonding the grounds together will cost maybe $10 worth of wire. It's
cheap insurance.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

That is not a wise idea. If your mast takes a direct hit, or if there is one
nearby, there is a possibility that some of the energy will go into the house
via that ground rod. Antenna grounds should always be isolated from
housewiring grounds.

Antenna grounds should always be isolated from
housewiring grounds.

==============================

Unless your antenna is under another distant thundercloud you must have
suicidal tendencies. ;o)