Meeting held April 22, 2002.
Our April meeting (presented jointly with the Washington Association of Production Services - WAPS) was a look at the National Electrical Code (NEC) as it applies to audio & video systems. Our guide was Mark Rogers, AES PNW Committee member and Registered Professional Engineer (PE) at Seattle consulting firm The Greenbusch Group*, who gave a very interesting and nuanced look at details, implications, and ambiguities in the Code. The dinner meeting was held at the Shilla restaurant in Seattle, and over 30 persons attended.
The NEC is published by the National Fire Protection Association, and its proper title is NFPA 70. Surprisingly, it has applied to audio since the 1940's. It is not a design guide or a manual of good practices; it is solely concerned with protection from fire and shock. It doesn't care if a system built according to its requirements buzzes, hums, or even functions. A reader may find it to be obtuse and illogical; however, if you go back in time through the various editions and follow the evolution of a particular entry, it does make sense. In the 1950's, the code book was the size of an oversized matchbook; today it is over 600 8 1/2" x 11" pages. The Code evolves, in part, as a reaction to catastrophes.
Sound systems are covered in Article 640, data systems in Article 645; low-voltage wiring is in Article 725, and fire alarms are in Article 760. Telephone and Telegraph Communications Systems are covered in Chapter 8, and no other part of the NEC applies to items covered there (except in a few specified cases), which is a testament to the power of the original Ma Bell.
There are numerous citations in the Code where the item under discussion has to meet the approval of the "AHJ", which stands for "Authority Having Jurisdiction", and means whichever Governmental entity, represented by a particular individual, is looking at your installation at that moment, and which has the power to deny permission to use that installation. That individual is Judge, Jury, and Executioner all wrapped up into one person. Where the word "approved" is used in the NEC, it means whatever is acceptable to the AHJ, specifically to that entity inspecting your work. Mark noted that the meaning of the NEC varies subtly from place to place, and from time to time, depending on the interpretation of the particular AHJ. Additionally, many jurisdictions revise the Code to suit themselves. Seattle has a booklet, titled "1999 Seattle Electrical Code Supplement, Ordinance 119507, Effective July 29, 1999" (and there may be a more recent one), put out by the Department of Design, Construction, and Land Use. He called our attention to its Section 106, "Alternate Methods", which essentially says that an individual Inspector has a very wide latitude to determine acceptability. Mark pointed out that if there is something you have a question about, it is best to take the time and go down to the office of the AHJ, to get their advice and opinions beforehand, so they can advise you IN WRITING how you can achieve your goal. They appreciate that you ask first, and having it in writing from the central office will make it easier with an individual inspector. He also noted that the Federal Government is exempt from all local laws and jurisdictions.
We talked about the role of Underwriters' Laboratories (UL); many AHJ's require UL recognition of any electrical equipment used on a jobsite. Mark pointed out that UL is not named in the NEC, and is not a legally-mandated monopoly. There are several recognized approval organizations, and each AHJ has the option of recognizing (or not) a particular organization. UL seems to be the most widely-accepted. He also talked about the differences between "Listed", "Labeled", "Identified", and "Marked", as defined by the NEC.
"Listed" is defined as "Equipment, materials, or services included in a list published by and organization that is acceptable to the authority having jurisdiction and concerned with evaluation of products or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluation of services, and whose testing states that either the equipment, material, or services meets identified standards or has been tested and found suitable for a specific purpose."
We then went on to look at specific parts of the NEC.
725-5 says "...Access to equipment shall not be denied by an accumulation of cables...", and further specifies that you don't lay cables on top of suspended ceiling tiles; rather, they should be raised above the tiles in conduits, raceways, using d-rings, or other means.
725-7 "...circuits shall be installed in a neat and workmanlike manner..." So the AHJ can ding you for being sloppy.
725-10 is new for 2002, and says "...circuits must be identified..." at terminations and at junction boxes. However, the method of labeling is not specified.
We learned about classes of wiring: Class 1 is essentially the same as wallpower, lighting, etc. 120 volt doorbell wiring also is Class 1. Class 2 is less than 30 volts, and 100 VA. Class 3 has higher voltage and lower current than Class 2.
Article 725-41 says there are only 5 things that can be Class 2 or 3:
A listed Class 2 or Class 3 transformer; a listed Class 2 or Class 3 power supply; other listed equipment marked to identify the Class 2 or Class 3 power source (except for thermocouples); listed computer equipment with limited power circuits; and dry cell batteries of 30 volts or less with a capacity equal to or less than series connected No. 6 carbon zinc cells. (Again, the listing has to be done by UL or other AHJ recognized Lab.) If it's not Class 2 or Class 3, then it must be Class 1.
Mark pointed out that all Class 2 & 3 cables must be listed, and that Canare cable is not listed, has never been listed, and maybe never will be listed, due to Canare's lack of interest in obtaining a listing. So an installation which relies on Canare mic cable may need to be redone when inspected by an AHJ. He also noted that putting unlisted cable into a conduit does not make it acceptable. Mark stated that Class 2 & 3 wiring could not be inside the same cable or conduit as Class 1 wiring, however, newly in the 2002 Code is a provision that if the wires are separated by 1/4", they could now be in the same enclosure or box. Also new is a provision that they could go through the same opening if one is in a piece of flex tubing when it goes through the opening.
Article 725.58 concerns cable support, in that cables "...shall not be strapped, taped, or attached by any means to the exterior of any conduit or raceway...". Article 725.61 has a new clause which states that cables which are abandoned shall be removed, and not permitted to remain in place. As an aside, he mentioned that PVC jacket insulation, which is widely used because of cost, is very toxic when burned, as there is a chemical reaction which creates chlorine gas, so be very careful with that. (Your Scribe wondered then, and still wonders now, why more firefighters are not killed from this.) (In a subsequent exchange, Mark pointed out that "That's why they go into the fire wearing breathing apparatus.")
Article 640, which specifically deals with audio equipment, was largely unchanged since 1956. In the 1999 Code, it was totally replaced. There have been some changes in the 2002 Code; users should beware, as some jurisdictions have not yet adopted the 2002 Code and are still using 1999.
Part A names other Articles in the NEC covering audio equipment; a Fine Print Note (FPN) in 640-2 specifies that all audio signals are non-hazardous except for amplifier outputs (although it doesn't specify POWER amplifiers).
Part B (640.22) is for Permanent Audio System Installations, and allows you to choose between powering an equipment rack with a plug, or hard wiring it in. You specifically can't bring a bunch of power cords out of a rack and plug them into a bunch of duplexes on the wall. Mark pointed out that the 1999 version apparently prohibits wooden racks, and specifies that they are made of metal (this was fixed in 2002). Article 640.23 declares that the conduit fill requirements of Table 1 in Chapter 9 apply to audio cables, a requirement which dates to the 1930's. There is no similar rule for data or telephone cabling. He highlighted that 640-25 specifies that speaker enclosures put into a fire rated ceiling must be listed for that purpose, or installed in a can listed for that purpose, or into a gypboard box with that rating. This is a VERY expensive retrofit if overlooked when designing the sound system.
Part C concerns Temporary and Portable Sound Systems, and 640-41 has rules for multi-pole power connectors: there has to be appropriate strain relief on each connector; they must not be able to mate with connectors with a different ampere rating; and power connectors and speaker connectors must be incapable of mating. 640-42 discusses Use of Flexible Cords and Cables, which must comply with Article 400. Power cables to equipment racks must be Extra Hard Usage, per Table 400-4. 640-44 says that equipment not listed for outdoor use shall have "...appropriate protection...from adverse weather conditions...to prevent risk of fire or electric shock..."
Mark had earlier emphasized that the purpose of the safety ground on audio equipment is to create a ground path for an electrical fault, so as to cause the circuit breaker to trip when a fault condition occurs. Lifting the safety ground, even if it eliminates an audio hum or buzz, is not legal and not safe.
He mentioned that when you are designing your sound system, you need to know if it requires Class 1, 2, or 3 wiring, and to know that you need to know how it's going to be used. An amp wired in stereo may be able to use lesser wire than if it's wired in bridged mono. He went on to state that amps must be labeled for the class of wiring necessary for their usage; some amplifier manufacturers like Crown have been slow to provide and show this information, so be sure to check before you install or you may get dinged.
Mark also mentioned that the City of Seattle doesn't require a permit for a sound system which uses less than 1000' of wire; presumably, that means that a sound system using MORE than 1000' of wire must have a permit.
Finally, he said that Article 645 applies to Information Technology (IT) equipment, but it applies only within computer rooms. It doesn't apply to terminals, personal computers, etc.
He said that those wishing to find more discussion of power issues can find it at www.mikeholt.com
Thanks to Mark Rogers for a very informative meeting.