Hello to all and thanks for any help you can provide me.
Some time back I looked into installing a wifi antenna on the outside of
my brick office building here in town. I would offer free wifi to the
immediate area, shops, coffee houses, etc. and perhaps get some free
advertising out of it.
When I investigated the installation of such an antenna I was stopped in
my tracks because of the bonding (grounding) requirements. The need to
install #6 copper wire from the antenna to the building ground on a
direct external-to-the building path was something I was not prepared for.
Yesterday, the lottery agency had a decent size (bigger than home size)
satellite dish installed on the roof of our building. There is a small
store upstairs from me and this will replace the phone connection they
had been using all these years.
As I look at the installation from the ground I can see what looks to be
the coax wire and a greenish wire leading from the dish mast to the base
of a vent pipe that has been on the roof. They lead in together at that
point. The store is below. The roof is an A-frame and made of wood as is
the entire building more or less.
Question: Is this to code? I do not believe it is since the ground wire,
if that's what it is, leads inside the building somewhere and not
externally to the main ground. If hit by lightning it would direct the
energy into the building which is wrong.
Second, it leads away from the building bonding point, which is down on
my ground level in the electrical room at one end of the building.
My hunch is it has been connected to a water pipe or electical conduit
in the ceiling or wall.
I'd like to call the town electrical inspector but I want to make sure
I am correct in this. The theory of bonding at least and the need for
an external lead to building bonding point.
Recently, a building was hit by lightning in town and the damage went
from the roof down three floors and was very extensive.
Can anyone advise me on this?
First, in real life many cable, internet, and wireless phone
installers are not grounding the antennae properly.
As a matter of fact, in my area of the country, some do not ground at
all and get by with it because their are no permitting or inspections.
So far they have been lucky. One of these days lightning is going to
hit one of these antennae and all heck is going to happen.
However, the big guys like Bell telephone, go to great lengths to
install proper grounding and lightning protection.
For grounding some of the 2005 NEC requirements are pasted below.
It sounds complicated but it is not. Talk to your local electrical
inspector (AHJ) and he might provide more details.
800.93 Cable Grounding. The metallic sheath of communications
cables entering buildings shall be grounded as
close as practicable to the point of entrance or shall be
interrupted as close to the point of entrance as practicable
by an insulating joint or equivalent device.
FPN: See 800.2 for the definition of point of entrance.
IV. Grounding Methods
800.100 Cable and Primary Protector Grounding. The
metallic member(s) of the cable sheath, where required to
be grounded by 800.93, and primary protectors shall be
grounded as specified in 800.100(A) through 800.100(D).
(A) Grounding Conductor.
(1) Insulation. The grounding conductor shall be insulated
and shall be listed as suitable for the purpose.
(2) Material. The grounding conductor shall be copper
or other corrosion-resistant conductive material, stranded
(3) Size. The grounding conductor shall not be smaller
than 14 AWG.
(4) Length. The primary protector grounding conductor shall
be as short as practicable. In one- and two-family dwellings,
the primary protector grounding conductor shall be as short as
practicable, not to exceed 6.0 m (20 ft) in length.
FPN: Similar grounding conductor length limitations applied
at apartment buildings and commercial buildings help
to reduce voltages that may be developed between the
building's power and communications systems during
Exception: In one- and two-family dwellings where it is
not practicable to achieve an overall maximum primary
protector grounding conductor length of 6.0 m (20 ft), a
separate communications ground rod meeting the minimum
dimensional criteria of 800.100(B)(2)(2) shall be driven,
the primary protector shall be grounded to the communications
ground rod in accordance with 800.100(C), and the
communications ground rod shall be bonded to the power
grounding electrode system in accordance with 800.100(D).
(5) Run in Straight Line. The grounding conductor shall
be run to the grounding electrode in as straight a line as
(6) Physical Damage. Where necessary, the grounding
conductor shall be guarded from physical damage. Where
the grounding conductor is run in a metal raceway, both
ends of the raceway shall be bonded to the grounding conductor
or the same terminal or electrode to which the
grounding conductor is connected.
(B) Electrode. The grounding conductor shall be connected
in accordance with 800.100(B)(1) and (B)(2).
(1) In Buildings or Structures with Grounding Means.
To the nearest accessible location on the following:
(1) The building or structure grounding electrode system
as covered in 250.50
(2) The grounded interior metal water piping system, within
1.5 m (5 ft) from its point of entrance to the building, as
covered in 250.52
(3) The power service accessible means external to enclosures
as covered in 250.94
(4) The metallic power service raceway
(5) The service equipment enclosure
(6) The grounding electrode conductor or the grounding
electrode conductor metal enclosure
(7) The grounding conductor or the grounding electrode of
a building or structure disconnecting means that is
grounded to an electrode as covered in 250.32
For purposes of this section, the mobile home service
equipment or the mobile home disconnecting means, as
described in 800.90(B), shall be considered accessible.
(2) In Buildings or Structures Without Grounding
Means. If the building or structure served has no grounding
means, as described in 800.100(B)(1), the grounding conductor
shall be connected to either of the following:
(1) To any one of the individual electrodes described in
250.52(A)(1), (A)(2), (A)(3), or (A)(4)
(2) If the building or structure served has no grounding
means, as described in 800.100(B)(1) or (B)(2)(1), to an
effectively grounded metal structure or to a ground rod or
pipe not less than 1.5 m (5 ft) in length and 12.7 mm
(1 2 in.) in diameter, driven, where practicable, into permanently
damp earth and separated from lightning conductors
as covered in 800.53 and at least 1.8 m (6 ft) from
electrodes of other systems. Steam or hot water pipes or
air terminal conductors (lightning-rod conductors) shall
not be employed as electrodes for protectors.
(C) Electrode Connection. Connections to grounding electrodes
shall comply with 250.70.
(D) Bonding of Electrodes. A bonding jumper not smaller
than 6 AWG copper or equivalent shall be connected between
the communications grounding electrode and power
grounding electrode system at the building or structure
served where separate electrodes are used.
Exception: At mobile homes as covered in 800.106.
FPN No. 1: See 250.60 for use of air terminals (lightning
FPN No. 2: Bonding together of all separate electrodes
limits potential differences between them and between their
associated wiring systems.
800.90 Protective Devices.
(A) Application. A listed primary protector shall be provided
on each circuit run partly or entirely in aerial wire or
aerial cable not confined within a block. Also, a listed primary
protector shall be provided on each circuit, aerial or
underground, located within the block containing the building
served so as to be exposed to accidental contact with
electric light or power conductors operating at over 300
volts to ground. In addition, where there exists a lightning
exposure, each interbuilding circuit on a premises shall be
protected by a listed primary protector at each end of the
interbuilding circuit. Installation of primary protectors shall
also comply with 110.3(B).
FPN No. 1: On a circuit not exposed to accidental contact
with power conductors, providing a listed primary protector
in accordance with this article helps protect against other
hazards, such as lightning and above-normal voltages induced
by fault currents on power circuits in proximity to
the communications circuit.
I guess this is where I'm confused as all of the above possible means
of grounding seem to allow the wire to lead INTO the building rather
than remain outside of it. Therefore, allowing the energy from a direct
strike to enter the building.
The TV antenna on my home as a child had a ground wire that lead
straight down the side of our chimney and into the ground via a
grounding rod. It was the same rod that the house electrical panel was
bonded to. A wire from that main panel lead to the outside directly to
this rod. To me, this seems the best approach.
What has changed?
Also see 810.21 for grounding requirements of antenna structures
You can keep the coax shield bonding conductor short by running the coax
on the outside of the structure to the vicinity of the grounding
electrode and entering the structure at this point. But 810.21 requires
a structure to be grounded as well which will require a conductor to be
run from the antenna location to the ground rod.
810.21 (G) specifically allows the grounding conductor to run inside or
outside of the building. Section E however requires the conductor to
"(E) Run in Straight Line. The grounding conductor for an antenna mast
or antenna discharge unit shall be run in as straight a line as
practicable from the mast or discharge unit to the grounding electrode."
I would bet a dollar to the whole in a donut that the grounding
conductor does not run to any of the points named in 810.21.
810.21 Grounding Conductors ? Receiving Stations.
Grounding conductors shall comply with 810.21(A) through (J).
(A) Material. The grounding conductor shall be of copper, aluminum,
copper-clad steel, bronze, or similar corrosion-resistant material.
Aluminum or copper-clad aluminum grounding conductors shall not be used
where in direct contact with masonry or the earth or where subject to
corrosive conditions. Where used outside, aluminum or copper-clad
aluminum shall not be installed within 450 mm (18 in.) of the earth.
(B) Insulation. Insulation on grounding conductors shall not be required.
(C) Supports. The grounding conductors shall be securely fastened in
place and shall be permitted to be directly attached to the surface
wired over without the use of insulating supports.
Exception: Where proper support cannot be provided, the size of the
grounding conductors shall be increased proportionately.
(D) Mechanical Protection. The grounding conductor shall be protected
where exposed to physical damage, or the size of the grounding
conductors shall be increased proportionately to compensate for the lack
of protection. Where the grounding conductor is run in a metal raceway,
both ends of the raceway shall be bonded to the grounding conductor or
to the same terminal or electrode to which the grounding conductor is
(E) Run in Straight Line. The grounding conductor for an antenna mast or
antenna discharge unit shall be run in as straight a line as practicable
from the mast or discharge unit to the grounding electrode.
(F) Electrode. The grounding conductor shall be connected as follows:
(1) To the nearest accessible location on the following:
a. The building or structure grounding electrode system as covered in
b. The grounded interior metal water piping systems, within 1.52 m (5
ft) from its point of entrance to the building, as covered in 250.52
c. The power service accessible means external to the building, as
covered in 250.94
d. The metallic power service raceway
e. The service equipment enclosure, or
f. The grounding electrode conductor or the grounding electrode
conductor metal enclosures
(G) Inside or Outside Building. The grounding conductor shall be
permitted to be run either inside or outside the building.