Grounding Antenna Question

[Humbled Survivor]

Can I ground out my outdoor FM antenna from the pole?

Does the negative of the coaxial cable have to be grounded?

Which method is best for preventing lightening strikes?

 

[Phil Allison]

"Humbled Survivor"

Can I ground out my outdoor FM antenna from the pole?

** Yep.

The pole needs to be linked to metal plumbing with a heavy gauge copper
wire.

Does the negative of the coaxial cable have to be grounded?

** If it is isolated by a "balun", then yep - it a good idea too.

Which method is best for preventing lightening strikes?

** Can I suggest you make your peace with god right now ??




.... Phil

 

[Jamie]

Ref: NEC 810.15, 810.20, 810.21

Both the antenna mast and the signal lead-in (via a listed antenna
discharge unit) should be grounded IAW the above sections.

Nothing prevents lightning strikes but the effects can be mitigated.

actually, grounding it will attract near by strikes, but what ever..

THe emf pulse of a strike directly on a grounded mast will more than
likely cook the front end of what ever is connected to it and maybe
even jump around a bit.


Jamie

 

[bud--]

But the provisions of the NEC are not to protect from direct lightning
strikes to an antenna - much more elaborate protection is required. They
can provide protection from other surge sources, like near strikes.

For best protection the ground from antenna line entry protectors must
connect with a short wire to the power earthing system. You want to
minimize the voltage between power and antenna wires.

actually, grounding it will attract near by strikes, but what ever..

Not according to what I read.

THe emf pulse of a strike directly on a grounded mast will more than
likely cook the front end of what ever is connected to it and maybe
even jump around a bit.

Hams with high antennas routinely protect from direct strikes to their
antennas. The rest of us are not likely to install the protection hams
install. But most of us do not have antennas as exposed as some ham
antennas.

 

[Jamie]

But the provisions of the NEC are not to protect from direct lightning
strikes to an antenna - much more elaborate protection is required. They
can provide protection from other surge sources, like near strikes.

For best protection the ground from antenna line entry protectors must
connect with a short wire to the power earthing system. You want to
minimize the voltage between power and antenna wires.



Not according to what I read.


Hams with high antennas routinely protect from direct strikes to their
antennas. The rest of us are not likely to install the protection hams
install. But most of us do not have antennas as exposed as some ham
antennas.

I am a HAM, so if you're getting your information from there, then you
better read between the lines..

Ham radio towers get hit many times in a season, they are not immune
from it.

NEC guide lines is there to protect people and that means the
structures people live or work in. THey don't give a rats ass about
antennas and devices connected to them, getting destroyed, they encourage
it. That way the lightning will be drawn away from the structure in hopes
that any thing conducting to ground, your antenna and mast, will steer
it away.

In most cases as for HAM radio, the radials are horizontal because most
of them put their beams at the vary top. normally you extend the mast
above the mounting axes. I add a

The tower our 2 meter equipment is at has lightning rods at the very
top with a beacon light, however, it does not always save the day.
antennas mounted on the side of the tower still get a nice strong pulse.

We use polyphaser protection devices, they seem to work the best for
what we need.

Jamie

 

[[email protected]]

But the provisions of the NEC are not to protect from direct lightning
strikes to an antenna - much more elaborate protection is required. They
can provide protection from other surge sources, like near strikes.

For best protection the ground from antenna line entry protectors must
connect with a short wire to the power earthing system. You want to
minimize the voltage between power and antenna wires.

Roger all of the above.

Re-reading the OP's question, he may have been asking if he could
ground the mast to the premise ground and bond the signal downlead
discharge gizmo to the mast's ground wire.

    \    /
     \  /---.
      ||    |
    m ||    |  R
    a ||    |  F
    s ||    |
    t ||    |
      ||    |
    ,-++---[ ]  discharge unit
   |  ||    |
   |         `---------RF-->
   |
   | grounding wire
__|+___
  || premise ground rod
  ||- Hide quoted text -

- Show quoted text -

If you get a 100,000 ampere lightning strike directly to anything
other than a metal building, the V=IR (voltage = current x resistance)
drop is going to raise the voltage of everything tied together many
many volts. All you can do is try to keep everything at the same
(elevated) voltage to avoid killing people/animals. This is done by
tying everything to the same local internal "ground". By having a low
impedance to earth ground using grounding rods and water pipes, you
try to minimize the difference between the local ground and the earth
ground. The current from a lightning strike will induce many
thousands of volts in any conductor a few feet long within 1000 feet
of the actual lightning strike. I have seen an arc form from a tv
lead-in wire to a ground when lightning hit 2000 feet away. The arc
jumped a 1" air gap, so the arc voltage was well over 1000 volts. A
protection device on the lead-in wire would probably have kept that
voltage under 100 volts. So grounding the antenna mast helps, but a
protection device on the lead-in is adding suspenders to a very weak
belt.

 

[bud--]

I am a HAM, so if you're getting your information from there, then you
better read between the lines..

Ham radio towers get hit many times in a season, they are not immune
from it.

And hams with high antennas are very likely to have good protection from
a direct lightning strike.

The OP is very unlikely to have antenna that is significantly exposed.

NEC guide lines is there to protect people and that means the structures
people live or work in. THey don't give a rats ass about
antennas and devices connected to them, getting destroyed, they encourage
it. That way the lightning will be drawn away from the structure in hopes
that any thing conducting to ground, your antenna and mast, will steer
it away.

The provisions in the NEC, which Rich referred to, are not intended to
protect from a direct lightning strike and won't protect from a direct
strike. NEC compliant wiring will not 'draw' the lightning away from the
structure.

 

[bud--]

It's illegal to use a pipe for ground in the US. The joints corrode,
and are high resistance to ground after years of use. You had to
install a bonding jumper around a water meter, years ago when it was
legal.

The NEC *requires* a metal water service pipe (minimum 10 feet long in
the earth) be used as an earthing electrode, just like it has since time
began. Connection now has to be withing 5 feet of the entrance to the
house, and meters still have to have a bond around. Because plastic
water service pipe is becoming more common a "supplemental" electrode is
now also required. A metal municipal water system is the best earthing
electrode that is available at a house.

Some fools have used the wrong pipe for natural gas, then another
fool assumed they were water lines and used them for a ground. The
results were explosive and sometimes fatal.

Gas service pipe is not allowed to be used as an earthing electrode by
the NEC. But gas pipe is grounded by branch circuits, like at gas furnace.

CSST (corrugated stainless steel tubing) is becoming real common for
interior gas pipe because it is so easy to use. It is easy to use
because the wall is so thin. There have been many fires from arcing
between the thin pipe and nearby grounded surfaces. I believe all the
manufacturers now require the pipe be bonded to the house earthing
system in a way that results in the gas supply pipe being an earthing
electrode. 'Properly' bonded CSST has also caused fires. A
recommendation by an electrical inspector is for electricians to not do
the bonding, then they will not be named in the lawsuit.

 

[[email protected]]

This is a fantasy, unless you have 1/4 " x 3" bus bars running the
length of your house, and from the main service panel to the ground
field, which would be maybe half an acre of bare welding cable
buried in the earth.

Otherwise, you simply can't get a low enough impedance to keep
the IR drop anywhere within reason.  And, the induced voltages across
various points such as plumbing and plugged-in appliances can
be lethal.  (later part of your post seems to agree with this.)

So, mostly, you want to try to conduct lightning strike currents
away from the building, not THROUGH the building.  So, what I have
is a ground rod driven directly under the antenna, and connected
to the mast via 4 gauge cable.  If the lightning current goes through
the house, it can easily set it on fire.

Jon

Jon, Please note that I said you can "try", I didn't say you "could"
keep the IR drop low. I agree with all your other comments.

 

[Phil Allison]

"bud--"


** AFAIK - the main reason TV antennas are required to be grounded is NOT
because of possible acts by a mighty and vengeful god.

The simple reason is that the antenna may become live AC supply voltage and
so make the TV set (and anything attached to it) inside the premises into a
lethal shock hazard.

This could be because an overhead power cable has detached in a strong wind
or because of an automobile accident etc.

ALTERNATIVELY - the antenna may become live due to a faulty equipment or
wiring inside the premises and so present a lethal hazard to any poor damn
fool who is game enough to get up on the roof for any reason.

Grounding the damn antenna any which way you can is essential.



..... Phil

 

[Phil Allison]

"bud--"

Other reasons are to earth static charges from the wind and control surges
induced by near strikes.

** Really .........

Wot a fucking, tenth wit num skull.





.... Phil

 

[bud--]

This is a fantasy, unless you have 1/4 " x 3" bus bars running the
length of your house, and from the main service panel to the ground
field, which would be maybe half an acre of bare welding cable
buried in the earth.

The way it is done is all wires - power, cable, phone, antenna, dish -
enter at about same location. Entry protectors for the signal wires
connect with a short wire to the power earthing system. A surge
protector at the service panel limits the voltage of power wires to the
earthing system. In an 'event' the building "ground" can rise thousands
of volts, but all the wires rise together.

It is not perfect protection. During an 'event' a pad mounted A/C
compressor may have its ground potential at the earth where it is
located. The power system, and power wires to the compressor, can be
referenced to the earthing system, which can thousands of volts different.

A ham with a high antenna would have a better earthing system and the
common reference point may not be at the power service.

Otherwise, you simply can't get a low enough impedance to keep
the IR drop anywhere within reason. And, the induced voltages across
various points such as plumbing and plugged-in appliances can
be lethal. (later part of your post seems to agree with this.)

So, mostly, you want to try to conduct lightning strike currents
away from the building, not THROUGH the building. So, what I have
is a ground rod driven directly under the antenna, and connected
to the mast via 4 gauge cable. If the lightning current goes through
the house, it can easily set it on fire.

Jon

Suppose you have a power system earthed by a single ground rod. The
antenna entrance to the house has a ground block, as required by the NEC
and an 18 ft ground wire to the power earthing system, as required by
the NEC. You add a ground rod at the entry protector. The NEC now wants
a #6 or larger bond wire to the power earthing system. Also suppose the
ground rods have a near miraculous 10 ohms resistance to earth.

Now suppose the antenna is hit by an "average" 20,000A strike. The
potential at the rod will be 200,000V from 'absolute' earth potential.
In general 80% of the voltage drop will be in the first 3 feet (which
probably results in arcing across earth at the rod). The potential of
the antenna lead will many tens of thousands of volts from the potential
of other wiring, referenced to the power system ground rod. There will
be major damage. The #6 (and your #4) bond wire help, but not
significantly. A lightning strike is a very short event and produces
relatively high frequency current components. The inductance of the wire
is much more important than the resistance. Inductance doesn't change
real fast with larger wire. There will be arc-over from the antenna and
down leads into the house anyway.

Now suppose there is a 5,000A surge to earth on the power earthing
system. The power system 'ground' will be 50,000V above 'absolute' earth
potential. It will be tens of thousands of volts from the ground rod for
the antenna. Power wires and antenna wires will be many thousands of
volts different. That will cause damage to anything connected to both.
Without the antenna ground rod the antenna lead would be lifted with
other house wiring. The same thing happens with a strike to a tree in
the yard with one rod nearer than the other.

I am not a fan of isolated ground rods. If you really want to protect
from a direct strike you need lightning rods.

And suppose the antenna lead goes close to a CSST gas pipe, which is
bonded as the manufacturer requires. There is an arc from the antenna
lead to the CSST which melts a hole in the 0.008" wall. If you are lucky
that just ignites the escaping gas and causes a fire. (My intent is to
comment on CSST, not so much the antenna ground rod.)

 

[bud--]

"bud--"



** AFAIK - the main reason TV antennas are required to be grounded is NOT
because of possible acts by a mighty and vengeful god.

The simple reason is that the antenna may become live AC supply voltage and
so make the TV set (and anything attached to it) inside the premises into a
lethal shock hazard.

This could be because an overhead power cable has detached in a strong wind
or because of an automobile accident etc.

ALTERNATIVELY - the antenna may become live due to a faulty equipment or
wiring inside the premises and so present a lethal hazard to any poor damn
fool who is game enough to get up on the roof for any reason.

Grounding the damn antenna any which way you can is essential.

.... Phil

Other reasons are to earth static charges from the wind and control
surges induced by near strikes.

 

[bud--]

bud-- wrote:



Well, if you do this, you probably end up destroying everything in
the house, including the wall outlets and Romex in the walls. I have
heard of people having this happen, where all the Romex was just
empty plastic tubes with burn holes every couple inches where the
copper vapor escaped. All the wall outlets were blown out of the
wall boxes and reduces to fragments. Having to run new Romex inside
all the interior walls runs something like $50K now.

It is, essentially, how hams protect high antennas that are likely to
get hit. The intersystem bonding is heavier and the earthing hams have
is much more extensive.

An electrical inspector in another forum has a weather station that is
on a metal post with the post tied to the power earthing system It has
been hit twice. Minimal damage on the first hit and with fairly minor
added protection he had no damage on the second hit. The weather system
has a data lead that comes down the pole.

My idea, which doesn't meet code, is to try to draw the main currents
AWAY from the rest of the house and possibly preserve some of the
appliances. Whatever is connected to the antenna will be complete
toast either way, but isolation may help some of the appliances
survive.

Jon

If you want to protect from a direct lightning strike install lightning
rods. Lightning rod protection is more complicated than you antenna
earthing scheme and your antenna will not substitute for a lightning
rod. Side flashes into the house are likely. And damage is much more
likely from power service surges and near strikes. Lightning rod systems
are required to be bonded to the power earthing system.

 

[bud--]

"bud--"


** Really .........

Wot a fucking, tenth wit num skull.

Wot an insightful (but typical) comment.