Article 820 - Code Basics
by Mike Holt for EC&M Magazine
Be careful with limited-energy coaxial cable.
Its easy to misinterpret 820.1 as limiting Article 820 to television or cable TV applications. But, it applies to any work you do installing coaxial cables to distribute limited-energy high- frequency signals. For example, if youre installing coax for a closed-circuit television in a security system, Article 820 applies (see Figure 820-1 un820-01 820-01 01.cdr). If you use coax to connect antennas to equipment [810.3], or for local area networks, you must follow Article 820 (see Figure 820-2 un820-02 820-01 02.cdr).
Perhaps the most important definition in Article 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 per 820.40(B). See Figure 820-3 un820-03 820-02.cdr. You must also know the point of entrance to determine the length of unlisted cable inside a building [820.50, Exception No. 3].
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, unless you run the cables in metal raceways (see 820.61 and 820.53(A)) or if the plenums are in habitable rooms or areas of a building where the primary purpose is not air handling [300.22(C)]. Coax installed beneath a raised floor doesnt need to be Type DP or plenum rated (see 300.22(D) and 645.5(D)(5)(c)).
Install cables in a neat and workmanlike manner. Where they run exposed, support them with straps, staples, hangers, or similar fittings designed and installed so as not to damage the cable.
Dont attach coaxial cable to, or support it with, raceway [300.1]. Support via cable tie to conduit is not an acceptable method (see Figure 820-19 un820-19 820-52D.cdr). There is one exception: You can support overhead (aerial) coax to a raceway mast intended for the attachment and support of communications cables (see Figure 820-20 un820-20 820-52Dx 820-10c 230-28.cdr). Dont support coax by, or attach it to, the power service mast.
Route cables so suspended-ceiling panels dont interfere with access to electrical equipment (see Figure 800-4 un800-04 800-05.cdr). If you install cables near framing members, protect them against physical damage from penetration by screws or nails by 1 1/4 in. separation from the face of the framing member, or by a suitable metal plate per 300.4(D). See Figure 820-5 un820-05 802-06 02 300-04D.cdr.
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 no less than 10 ft over swimming and wading pools, diving structures and observation stands, towers or platforms [680.8(B)]. See Figure 820-6 un820-06 820-10F3 680-08B.cdr.
[820.33] Ground the metallic sheath of coax to the earth (electrode) as close as practicable to the point of entrance to the building or structure (see Figure 820-7 un820-07 820-33.cdr). This doesnt mean you should drive a separate electrode. The practice of driving a ground rod at a convenient location and not bonding that ground rod to the power grounding electrode system is not permitted.
As the 820.33 FPN explains, one purpose of 820.33 is to limit the potential differences between CATV and other metallic systems (see Figure 820-14 un820-14 820-40D.cdr). So, connect the coax shield to the main grounding system. If theres a separate grounding electrode for the radio and television equipment, bond it to the power grounding electrode system with a conductor not smaller than 6 AWG (see Figure 820-13 un820-13 820-40D 01.cdr).
Not bonding the electrode to the power grounding electrode system creates differences in potential between the CATV and other systems, such as power and telephone-resulting in current flow from lightning strikes and high-voltage surges. This shock and fire hazard can easily destroy equipment connected to multiple systems (i.e., the cable tuner is common to power, CATV and phone).
[820.40] When grounding the coax sheath:
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 820-11 un820-11 820-40B1.cdr):
Listing and Markings
[820.50] When installing coax in a building, use cables listed for the purpose and marked per Table 820.50, unless:
Many electrical components and materials give off poisonous toxins when burned. In 300.22 (B) and (C), we find restrictions on the wiring methods and material 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 in a given location. Type CATV coax is suitable for general-purpose use, only-refer to Table 820.50 for other applications, such as risers and plenums.
Coax can be in the same raceway or enclosure with cables of any of the following (see Figure 820-16 un820-16 820-52A1a1.cdr):
Coaxial cable cannot be in any raceway or enclosure with conductors of electric light, power, or Class 1 circuits, unless:
In other applications, you must separate coax by at least 2 in. from any electric light, power or Class 1 circuit conductors-unless you install those electric light, power or Class 1 circuit conductors per a Chapter 3 wiring method (raceway, metallic or nonmetallic sheath, or UF cable). See Figure 820-18 un820-18 820-52A2x1.cdr).
To succeed with Article 820 installations, keep three primary concepts in mind. First, these are low voltage (under 60V) applications. Keep the proper separation between coaxial cabling and other systems. Second, dont 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, there is no special set of grounding physics for CATV or other coax applications. The basic 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 Article 820.
Copyright © 2002 Mike Holt Enterprises,Inc.