[R-390] Grounds

Sun Aug 2 15:56:25 EDT 2009

All: The NEC is correct in this case.  All the grounds need to be connected
together with large-gauge wire, so that any surge current (whether direct or
induced) cannot set up a large potential difference between the ground
systems.

In the commercial world we bond power and telco grounds together, and then
bond that to a ground ring around the building.  The ground ring around the
building is bonded to a ground ring around the tower (if any), and the tower
legs are bonded to the tower ground ring.  Three ground rods at the tower,
one ground rod at each corner of the building and more if the corners are
more than 15' apart, and all bonded to the appropriate ring.  Each coaxial
cable shield conductor is bonded to the ground ring around the building at
the point of entry into the building, and lightning protection is bonded to
the ground ring around the building.  Each telco and power entry or exit has
a suitable surge protector on it.  Inside the building, equipment grounds
are bonded to the bonding point for the power, telco, and coax shield
grounds.

This is a large condensation of guidance we received from both Polyphaser
and equipment vendors.

Hope this helps.

Dave WB4FUR

-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net]On Behalf Of rbethman
Sent: Wednesday, July 29, 2009 5:13 PM
To: R-390 at mailman.qth.net
Subject: Re: [R-390] Grounds

Dave,

The "codes" vary.

Now that I've said that, do NOT start a flame war folks!

State, County, Local Municipal codes are different in MANY instances.

Dave, I'm a fair bit East of you in Virginia.  The Cable TV folks, the
Telephone folks, and ANY one else installing a feed to the house - ALL -
attach "Their" grounds TO the Service entrance ground.

You are correct in the requirement that ALL grounds are bonded, (Now
THIS is a loose term!), together.  This keeps the potential at the same
level.

To be honest, my ground system is a WHOLE bunch better than what was
installed here by the power company.  My Copperweld grounds are 3/4" in
diameter.  Unlike that joke at the service entrance which I haven't
measured, but looks to be around 1/4" to 3/8" diameter.

I ran my ground grid to the service entrance ground also.

Bob - N0DGN

Dave or Debbie Metz wrote:
> Following this thread, I have a further question.  It is my
> understanding that all ground rods per the NEC need to be connected so
> that a danger situation does not develop.  The specific example is the
> ground rod (term used VERY loosely) that the cable company drives
> outside your house at the entry point on one side of the house and your
> ground rod at the opposite side of the house where the electric panel is
> situated is not connected but that indiscretion is a major danger in
> lightning protection.  As near as I can recall, the NEC requires ALL
> ground rods to be connected to maintain no possible potential
> difference. The danger as I understand is that the cable entrance has a
> ground, your TV is grounded to the "other" ground via the house wiring.
>   So,.... my question is: if we have additional grounds for our
> equipment, are we safer or more in danger if we do not connect them to
> the service entrance ground. Perhaps this is beyond the scope of this
> reflector but it seems like we have some engineers lurking in the
> background and I would really appreciate the science of this anomaly
> when talking about grounds to the entire group.
>
> 73's
> Dave
> Kj4JX
>
>
>
> rbethman wrote:
>
>> I'd suggest that you NOT have a lightning arrestor between the roof and
>> the ground braid.
>>
>> The metal roof will, at the top of the second story, tend to be a
>> lightning attractant.  Gounds for use to dissipate lightning strikes
>> SHOULD have any necessary bends be a SMOOTH radius.
>>
>> Standard electrical ground rods are indeed at LEAST 8 feet long, steel
>> cored copper, brand named originally COPPERWELD.  The strrel core is to
>> allow driving the rod into soils that aren't always easy to drive into -
>> like the clay and shale here in Virginia.
>>
>> Minimum of four ground rods, preferably ALL bonded together below the
>> surface of the soil with at least 1/4" copper conductor.
>>
>> In a power plant or substation we ALWAYS used a "grid" of 500 MCM bare
>> copper between all grounds.
>>
>> This will provide a Great counterpoise AND a very good ground for the
>> home itself.
>>
>> Bob - N0DGN
>>
>>> I'm not in that position at the moment, thank goodness, but I'd think
>>> that the more copper straps or braids you could put down to ground rods,
>>> the better. All of them loop-and-bend-free, of course, to keep the
>>> inductance as low as possible.
>>>
>>> Do please let us know what your results are, as you continue in this
>>> investigation.
>>>
>>>
>>>
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--
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|             AM Amateur Radio Operator    NØDGN                   |
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| Bob Bethman                \\\|///     " The absence of a danger |
|                           \\ ~ ~ //      signal does *NOT* mean  |
| rbethman at comcast.net      (/ @ @ /)      that everything is OK " |
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