Tune In to the Requirements of Art. 820
Overcome poor reception from the AHJ by knowing the inside track with limited-energy coax cable installations
It's easy to think the scope of 820.1 limits the requirements of Art. 820 to television or cable TV applications. However, it applies to any installation of coax cables that distribute limited-energy, high-frequency signals. For example, if you're installing coax for a closed-circuit television in a security system, Art. 820 applies. And if you use coax to connect antennas to equipment (810.3) or to set up local area networks, you must also follow the requirements set forth in Art. 820.
Perhaps the most important definition in Art. 820 is “point of entrance.” Knowing this is critical to meeting various grounding requirements, such as those in 820.33 and 820.40. The point of entrance is where the cable emerges from an external wall or a concrete floor slab, or from a rigid metal conduit or intermediate metal conduit grounded to an electrode according to the requirements of 820.40(B) (Fig. 1). You must also know the point of entrance to determine the length of unlisted cable inside a building (820.50, Exception No. 3).
Beat the heat.
When installing coax through fire-resistant rated walls, partitions, floors, or ceilings, use approved firestop methods and materials to maintain the fire-resistance rating. Remove the accessible portion of abandoned cables to limit the spread of fire or products of combustion within a building.
Install only plenum-rated cables in plenums and other spaces used for environmental air, unless they run in metal raceways [820.61 and 820.53(A)] or the plenums are located in habitable rooms or areas of a building where the primary purpose isn't air handling [300.22(C)]. Coax installed beneath a raised floor doesn't need to be Type DP or plenum-rated [300.22(D) and 645.5(D)(5)(c)].
Install cables in a neat and workmanlike manner. If they're exposed, support them with straps, staples, hangers, or similar fittings designed and installed so as not to damage the cable.
Don't attach coaxial cable to, or support it with, raceway (300.1). Support via “cable tie to conduit” isn't an acceptable method either (Fig. 2). However, there is one exception: You can support overhead, or aerial, coax to a raceway mast intended for the attachment and support of communications cables. Don't support coax by, or attach it to, the power service mast.
Route cables so suspended-ceiling panels don't interfere with access to electrical equipment. If you install cables near framing members, separate them by 1.25 in. from the face of the framing member, or by a suitable metal plate to protect them against screws or nails [300.4(D)].
If you install cables in hazardous (classified) locations, follow Chapter 5 requirements. Where practicable, leave a separation of at least 6 ft between communications wires and cables on buildings and lightning conductors. CATV coax must be suspended at least 10 ft above swimming and wading pools, diving structures and observation stands, towers, or platforms [680.8(B)].
Ground the metallic sheath of coax to the earth (electrode) as close as practicable to the point of entrance to the building or structure. This doesn't mean you should drive a separate electrode. The practice of driving a ground rod at a convenient location without bonding it to the power grounding electrode system isn't permitted.
As the 820.33 FPN explains, one purpose of 820.33 is to limit the potential differences between CATV and other metallic systems. Connect the coax shield to the power grounding electrode system, and if there's a separate grounding electrode for the radio and TV equipment, bond it to the power grounding electrode system with a conductor no smaller than 6 AWG.
Not bonding the electrode to the power grounding electrode system creates differences in potential between the CATV and systems like power and telephone, which results in current flow from lightning strikes and high-voltage surges. This shock and fire hazard can destroy equipment connected to multiple systems like the cable tuner, which is common to power, CATV and phone.
When grounding the coax sheath:
Use an insulated grounding conductor listed for the purpose.
Use a grounding conductor made from a corrosion-resistant conductive material. Copper conductors may not be smaller than 14 AWG.
When grounding the coax sheath, adhere to the following requirements:
Make the primary protector-grounding conductor as short as practicable. In one- and two-family dwellings, it may not exceed 20 ft in length. If that length isn't practicable, you can connect it to a driven rod if you bond the rod to the power grounding electrode system with a conductor no smaller than 6 AWG (Fig. 3).
Run the grounding conductor to the grounding electrode in as straight a line as practicable.
Guard the grounding conductor from physical damage, as necessary.
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 (Fig. 4).
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:
The building or structure grounding electrode system, as covered in the requirements of 250.50
The grounded interior metal water-piping system, within 5 ft of its point of entrance to the building [250.52(A)(1)]
Accessible bonding means, such as 6 in. of 6 AWG copper conductor connected to the service equipment or raceway [250.94]
The metallic service raceway
The service equipment enclosure
The grounding electrode conductor or the grounding electrode conductor metal enclosures
Making your mark.
When installing coax in a building, use cables listed for the purpose and marked according to Table 820.50. However, those guidelines don't apply in certain situations. You can disregard the table's requirements if the cable enters the building from the outside and runs in rigid metal conduit or intermediate metal conduit, and the raceway is grounded to an electrode per 820.40(B). Installations in which the length of the cable within the building, measured from its point of entrance, doesn't exceed 50 ft, and the cable enters the building from the outside and terminates at a grounding block are also exempt from those guidelines.
Many electrical components and materials give off poisonous toxins when burned. Both 300.22(B) and (C) contain restrictions on the wiring methods and materials you can use in areas of a building used for handling environmental air. These restrictions help reduce hazards that arise from the burning of components of an electrical system. Thus, you must pay careful attention to the listings and markings of the materials you use in a given application at each location.
Playing by the rules.
Coax can be installed in the same raceway or enclosure with cables of any of the following:
Class 2 and Class 3 circuits — Art. 725
Power-limited fire alarm circuits — Art. 760
Optical fiber cables — Art. 770
Communications circuits — Art. 800
Low-power, network-powered broadband communications circuits — Art. 830
Coax cable can't run in any raceway or enclosure with conductors of electric light, power, or Class 1 circuits, unless they're separated by a barrier or the power circuit conductors are introduced solely for power supply to the coax system distribution equipment. The power circuit conductors must have a minimum of 0.25 in. separation from the coax.
In other applications, you must separate coax from any electric light, power, or Class 1 circuit conductors by at least 2 in., unless you install those conductors according to a Chapter 3 wiring method for raceway, metallic or nonmetallic sheath, or UF cable.
To comply with Art. 820, keep three concepts in mind. First, these are low-voltage (under 60V) applications, so you need to keep the proper separation between coax cabling and other systems. Second, don't violate the fire integrity of a structure. Use approved firestop methods and materials, and take the necessary steps to minimize any loss of fire-resistance. Third, no special set of grounding physics exists for CATV or other coax applications. The engineering principles that apply to power installations also apply to limited-energy, high-frequency coax installations, such as CATV. So be sure you eliminate any potential differences between your coax installation and other metallic items. Keeping these three concepts in mind will help you eliminate any potential violations of Art. 820.