National Electrical Code Articles and Information

National Electrical Code Top Ten Tips: Article 640, Audio Signal Processing, Amplification, and Reproduction Equipment

In the early days of recording studios, this equipment was often hooked up in a manner that created birds' nests of wiring, overloaded cabling, and other problems. If you look at the typical home entertainment center, you get the idea. In areas with limited egress (e.g., sound studio) or with large assemblies of people (e.g., churches), the absence of a standard like Article 640 could prove tragic. That same issue exists with temporary and portable audio equipment, which Article 640 covers.

Article 640 does not explicitly say it doesn't apply to small installations such as home theater systems, but from the context this seems to be the case. That does not prevent you from applying relevant portions of Article 640 to such installations.

1. Before installing any audio equipment in any location, read 640.1 to see if Article 640 applies. Consider applying Article 640 even where it's not required, for example in a home theater system.
    
2. Other Articles may also apply [640.3]. Location is the key factor in determining which one(s) to also apply.
    
3. Locate the equipment so as to guard against environmental exposure or physical damage [640.4]. There may be more to this than a casual consideration would reveal. Look at such things as foot traffic paths, window and door locations, position relative to bathroom facilities (would an overflowing toilet on the floor above endanger this equipment?), and facility maintenance activities.
    
4. You can't install wiring such that it blocks access to panels [640.5]. This requirement is redundant, if you understand and correctly apply 640.6.
    
5. Install the equipment and cabling in a neat and workmanlike manner [640.6]. This used to be widely open to interpretation. Decades ago. Today, there are published installation standards in addition to industry standard practices. There are also looms, restraints, clips, straps, hangers, and other devices designed to help the installer neatly route, support, and protect cable and wiring. Some manufacturers even make kits and systems for this purpose. There is no excuse for birds nest wiring, or even wiring that runs at odd angles instead of following a nice neat path.
   
   In addition to neat routing, workmanlike installation mandates proper and thorough labeling. The days when handwritten labels were acceptable are long gone; use a label printer to make legible, durable labels efficiently.
   
   Wire bending is an issue. Electronics technicians are used to making small radius 90 degree bends in small wiring (e.g., 22 AWG) using needle nose pliers. The radius achieved by this technique is too small for power wiring to result in a safe installation. Doing this with signal cables can easily result in attenuation that severely degrades system performance; in fact, it will normally destroy the cable. Don't exceed the bend radius limits of conductors.
    
6. Connect wireways and auxiliary gutters to equipment "grounding" conductors [640.7], understanding that the NEC uses archaic and inaccurate terminology in reference to such conductors. Article 100 of the NEC defines grounding as connecting to the earth (dirt). An equipment grounding conductor (EGC) is actually an equipment bonding conductor. A mistake some installers make is they connect these wireways and gutters to a ground rod. That does not come anywhere close to achieving what an EGC connection achieves, and it will result in differences of potential. You can then expect system performance problems, equipment failures, and potentially lethal touch hazards.
    
7. If you supply the audio system from a branch circuit, keep all parts of it at least 5 ft from the inside wall of any pool, spa, hot tub, or fountain [640.10].
    
8. If you use a portable cord, it must be suitable for the use [640.21]. Article 640 doesn't go on to explain what "suitable" means here. Portable cord manufacturers state on the packaging what uses a particular cord is suitable for, and you can find this information on their Websites. In addition to having the correct amperage rating, a cord must be designed for the particular environment in which it's being used.
    
9. Do not ground metal equipment racks and enclosures, even though 640.22 says to do this. As in many other NEC requirements, the meaning here is "bond." Grounding these provides absolutely no benefit, but may introduce problems. You want to bond them, so you eliminate differences of potential. See the Article 100 definitions of grounding and bonding. Refer to Article 250 Part V for bonding requirements in general.
    
10. For portable and/or temporary audio system installations, see Part III of Article 640.