Article 810 - Radio and Television Equipment
by Mike Holt for EC&M Magazine
Do you know how to prevent one of the leading causes of electrocution?
If you install a satellite dish antenna, you must follow Article 810. This article provides the requirements for television and radio receiving equipment, such as the satellite antenna already mentioned, or for any other receiving equipment for television signals. This article also applies to such other items (see Figure 810-1 un810-01 810-01.cdr) as:
Keep in mind that Article 810 addresses only those issues specific to this kind of equipment. You still must supply power per the requirements of Chapters 1 through 4. Wiring for audio signal processing, amplification and reproduction equipment must comply with Article 640. If you use coaxial cables to connect antennas to equipment, you must comply with Article 820. See Figure 810-2 un810-02 810-03.cdr.
The wiring for a community television antenna must comply with this article, and the distribution coaxial wiring must comply with Article 820. Dont confuse a Community Television Antenna [Article 810] with Community Antenna Television [Article 820]. A community TV antenna can be for multiple units such as for apartments, condominiums, motels and hotels. On the other hand, community antenna television (CATV) is utility-supplied cable TV.
Part II of Article 810 addresses receiving equipment, while Part III addresses amateur transmitting and receiving equipment. Lets look at Part II, next.
[810.12] You must securely support outdoor antennas and lead-in conductors. Secure the lead-in conductors to the antenna.
[230.28] Do not attach lead-in conductors to the electric service mast (see Figure 810-3 un810-03 810-12 230-28.cdr).
[810.13.] Avoid contact with conductors of other systems (see sidebar). Outdoor antennas and lead-in conductors must not cross over open conductors of electric light or power circuits. Keep them well away from all such circuits to avoid the possibility of accidental contact. If you cant avoid proximity to open electric light or power service conductors of less than 250V between conductors, provide a clearance of at least 2 ft. between them. Where practicable, install antenna conductors so they dont cross under open electric light or power conductors.
[810.14] Make any splices mechanically secure with approved splicing devices or by other means that wont weaken the conductors.
[810.16] When you size the outdoor antenna conductors for receiving stations, use Table 810.16(A). Outdoor antennas must be strong enough to withstand ice and wind loading conditions. You must locate these well away from power lines to avoid accidental contact. That includes addressing the possibility that the antenna might fall onto power wiring below it-if you dont mount the antenna above power wiring, you prevent that problem.
The three sets of clearances in 810.18 are outdoors, indoors, and enclosures:
[810.20] You must provide each conductor of a lead-in from an outdoor antenna with a listed antenna discharge unit (ground block). If you put a discharge unit inside the building, place it nearest the point of entrance-but not near combustible material. You can also place it outside the building, thus eliminating any potential problems stemming from location inside the building.
Grounding the receiving equipment is critical. If the mast is not properly grounded, induced voltage spikes from lightning strikes can destroy the low-noise block (LNB). They can also destroy the dc rotor motors that control the positioning of satellite dishes equipped with them. If the lead-in from an outdoor antenna is not properly grounded, induced voltage spikes from lightning strikes can destroy the receiver.
Ground the antenna discharge unit (see Figure 810-7 un810-07 810-20C.cdr), the antenna mast, and antenna discharge unit (ground block) per 810.21 (see Figure 810-8 un810-08 810-21.cdr). If an antenna mast is within 5 ft of an outdoor swimming pool, bond it to the pool common bonding grid [680.26(B)(5)]. See Figure 810-4 un810-04 810-15 680-26A5.cdr.
[810.21] Grounding conductors must be copper or another corrosion-resistant conductive material (stranded or solid), but insulation is not required. You can run the grounding conductors inside or outside the building. If copper, a grounding conductor must not be smaller than 10 AWG.
You must securely fasten these conductors in place, and provide protection from physical damage as needed. Where the grounding conductor runs in a metal raceway, bond each end of the raceway to the grounding conductor or the same terminal or electrode to which the grounding conductor is connected. Run the grounding conductor to the grounding electrode in as straight a line as practicable-this improves lightning protection. The reason you ground the antenna equipment in the first place is to limit the voltage imposed by lightning or by unintentional contact with higher-voltage lines. Lightning does not like to go around corners and through loops in the wire, which is why the grounding conductor needs to run as straight as practicable.
If the building or structure has no grounding means, terminate the grounding conductor to any of the individual grounding electrodes described in 250.52. Otherwise, connect the grounding conductor to the nearest accessible location of one of the following (see Figure 810-9 un810-09 810-21F1.cdr):
Bond the electrode for the radio and television equipment to the buildings power grounding electrode system with a conductor not smaller than 6 AWG copper or equivalent (see Figure 810-11 un810-11 810-21J.cdr). The point of this is to prevent flashover between the electrodes, by equalizing the potential with a bonding jumper. Do not assume the earth can be your bonding jumper. That copper jumper will have a resistance so small as to be negligible, while the earth will have a resistance of millions or billions of ohms even on a wet day. To compare conductivity between a copper bonding jumper and the earth, rub the page youre reading between your fingers. That is taller than youd be, if you were to compress your height proportionately to the conductivity change that results from using earth instead of copper wire as a bonding jumper. Obviously, you arent going to function well at that height. Remember this when you are thinking about leaving the earth to serve as the bonding jumper between electrodes.
Correctly implementing Article 810 is fairly easy, if you remember the three concepts it addresses. First, this is very low voltage wiring-keep it away from power wiring. Second, secure the equipment so it is also away from power wiring with no chance of accidental contact. These first two concepts are important because so many people have died from accidental contact between radio/television equipment and power wiring.
Third, bond all electrodes together and to the common power electrode. This prevents flashover. Electricity is not trying to get back to the earth. Its trying to get back to the source-which is why usable electrical circuits are possible. If the path you provide is too high in resistance, electricity will find another-possibly lethal-way back to the source. When you need to safely install radio and television equipment, always go back to your own source: Article 810.
(SIDEBAR) The NEC Handbook says, One of the leading causes of electrical shock and electrocution, according to statistical reports, is the accidental contact of radio, television, and amateur radio transmitting and receiving antennas and equipment with light or power conductors. Extreme caution should therefore be exercised during this type of installation, and periodic visual inspections should be conducted thereafter.
Copyright © 2002 Mike Holt Enterprises,Inc.