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SAFETY SPOTLIGHT ON INCANDESCENT LIGHTING by Steve Pasternack, Internek Testing Services If you ask anyone about the kind of lighting they’d prefer to live with, incandescent is often the answer. True, it doesn’t pack as much brightening power per square inch as fluorescent. Nor does it keep cool easily around today’s increased building insulation values. So what fuels incandescent lighting’s continued popularity? Incandescent lighting fixtures are attractive, fairly inexpensive, and relatively easy to install. But despite how familiar an installer or inspector may be with incandescent lighting, the challenge is to safely handle its heat output Less Light For Your Bulb Two words sum up one downside of incandescent lighting: operational inefficiency. The culprit is incandescent lighting’s required heating process versus the arc discharge process employed in fluorescent and high intensity discharge (HID) lighting. Incandescent lighting consumes at least twice the amount of power that is required for moderately efficient arc discharge lighting. Switch on a fixture housing one 40-watt fluorescent bulb. To match that illumination from your incandescent fixture, you’ll require one 100-watt bulb. Maintaining Safety: A Question of Heat The primary disadvantage of incandescent lighting, including halogen designs, is not because you have to make the choice between more wattage or less light. The biggest potential problem lies in safety concerns due to the way incandescent light generates heat. An incandescent bulb operates by passing current through a fine tungsten alloy, causing it to heat to an incandescent (glowing) state. This process generates large quantities of heat that need to be dissipated safely. When installing chain supported or swag mounted fixtures, which are normally mounted at least a foot away from the field wiring box and building support, it’s fairly easy to limit the amount of heat being absorbed into the fixture’s field wiring area and supporting building structure. Heat absorption into the building structure is limited by the distance away from critical structures. Not so, however, for flush mounted and recessed fixtures, which are very close to, or may actually touch critical surfaces, thus making heat a potential problem. Today’s higher insulation ratings pose yet another safety concern for lighting designers-whose charter has become increasingly difficult in the wake of more stringent national regulations over the past 25 years. Driven by the demand for more efficient energy usage, these regulatory changes have caused wall and ceiling insulation ratings to almost double in new or remodeled home construction. It is not unusual today to see insulation values of Rl I in walls and R38 in ceilings, compared to the R19 values commonly used in ceilings built circa 1960.
Getting More Life From Your Wiring The current edition of the National Electrical Code’ specifies in section 410-11 that the fixture shall be of such construction or so installed that the conductors in outlet boxes shall not be subjected to temperatures greater than that for which the conductors are rated. The code further states in section 410-5, that fixtures near combustible material shall be so constructed or installed or equipped with shades or guards that combustible material will not be subjected to temperatures in excess of 90*C. In order to meet these requirements, the installer should be careful to install all thermal insulating barriers provided by the fixture manufacturer. These barriers prevent heat from exceeding 90’C on combustible material employed as supporting surfaces. It’s equally important to position provided insulating barriers properly, so that the field wiring area does not reach 60*C, or the marked minimum wire temperature determined after test by a Nationally Recognized Safety Testing Laboratory (NRTL) to the Standard for Safety Incandescent Lighting Fixtures (ANSL/UL 1571). Temperature control is critical since wire that’s used in an ambient temperature above its rated maximum tends to break down over time faster, thereby reducing its safe life expectancy. The bottom line is that heat kills wire insulation. Every 10 degrees that a wire is operated over the marked rating of its insulation can reduce its effective safe life by one half. Operate a 60*C wire with a life expectancy of 20 years at 70*C, and you’ll reduce its life by as much as ten years. The potential problems could lead to wire insulation breakdown, and fire or shock hazards. The opposite is equally true. Operate the same 60*C wire at 50*C and the lowered temperature lengthens the life of the wire. The installer should also never lamp a fixture in excess of its marked maximum bulb(s) rating, In addition, fixtures designed for domestic applications should never be installed in an environment normally above 40*C, unless the fixture is rated for a higher ambient temperature. This installation procedure is in accordance with the intent of ANSVUL 157 1. Fixtures Over Ten Years Old The unique or attractive appearance of some incandescent fixtures increases the likelihood that installers will rewire or reinstall fixtures over 10 years old. While older fixtures might be in good condition, chances are they were designed when there was less thermal insulation in ceilings and walls. Recall that today’s improved building insulation tends to trap added heat near combustible surfaces or in field wiring areas. Since many older fixtures have never been investigated to determine their thermal characteristics with the higher rated building insulation, it makes sense to employ wire rated for higher temperatures, and to use care in reviewing the supporting surface for combustibility. Also, using lower wattage bulbs will reduce the fixture’s heat output. Conclusion: Don’t Take Safety For Granted The incandescent lighting fixture is a familiar electrical product that will no doubt continue to light up many of our lives. Installers and inspectors, however, should be aware that, if installed improperly, it can be as hazardous as the most sophisticated lighting device sold today. Steve Pasternack is engineering manager for the Power Systems Group at Intertek Testing Services (ITS) of Cortland, New york, where he has been working for 28 years. During his career with ITS, he has held positions as senior and staff engineer, and has managed the Certified Ballast Manufacturers Certification Program, which included his involvement in ANSI 78 (lamp) and C81 (ballast) Committees. Throughout his career, he has been responsible for the evaluation of a wide range of products, including lighting fixtures and medical devices. ITS is a Nationally Recognized Testing Laboratory and issues the ETL Listed Mark
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