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.
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 or solid. (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 lightning events. 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 practicable. (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 rods). FPN No. 2: Bonding together of all separate electrodes limits potential differences between them and between their associated wiring systems. III. Protection
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.
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 connected. (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
250.50 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.
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