Some environments can pose difficult conditions for operating lighting systems, including damp and wet areas, corrosive environments, hazardous locations, areas that experience abnormal temperatures, areas that experience momentary power failures, and clean rooms. That means that either the light source must be able to operate properly under these conditions or the fixture must protect the light source from these conditions.
Damp And Wet Areas
If the environment exposes the lighting system to moisture condensation, then the location is a damp location. If the lighting system is exposed to direct impact by water, which will make the fixture wet, then the location is a wet location.
Fixtures for this environment must be approved for use by as required by the National Electrical Code® (NEC®), Section 410-4(a). Approval is gained by the local authority who has jurisdiction in interpreting the NEC. Damp location fixtures are specified for indoor or outdoor locations that experience dry or damp conditions only. Wet location fixtures are specified for indoor or outdoor locations that experience, dry, damp or wet conditions. Note that if a fixture installed in concrete will be in direct contact with the earth, it must be approved for use in wet locations.
Some environments contain fumes and vapors that corrode fixtures and supplementary components such as mounting hardware. Fixtures for corrosive environments must be approved for use as required by the NEC, Section 410-4(b,c). Approval is gained by the local authority who has jurisdiction in interpreting the NEC. Corrosive location fixtures are specially coated to protect them from corrosive fumes and vapors. They may also be enclosed or feature specially treated reflective surfaces.
In hazardous environments, the air contains flammable dust, gas or vapors that can combust if it comes into contact with electrical equipment, including lighting systems. Fixtures, wiring and controls must be approved for use as required by Section 500 of the NEC. In addition, equipment such as ballasts may be installed in a remote location if possible.
Section 500 classifies hazardous locations as Class I, II and III; each class represents two divisions, 1 and 2. Approval is gained by the local authority who has jurisdiction in interpreting the NEC.
Below is a general information guide concerning fixtures in fixed locations only; when designing a lighting system for hazardous locations, consult the NEC and all local authorities with jurisdiction over building construction.
Class I, Division 1 locations (NEC Section 500-5(a)) are environments where flammable vapors or gases (or a combustible mixture of them) result from normal operating conditions, repair or equipment breakdown. Fixtures designed for approved use in these locations are explosion-proof, completely enclosed to 1) prevent the escape or arcs or sparks that could ignite the flammable environment and 2) contain an explosion of a gas or vapor inside them.
Class I, Division 2 locations (NEC Section 500-5(b)) are environments where flammable gases or liquids are stored in tanks or other enclosed containers, and would be released only if the containers were damaged. Fixtures designed for approved use in these locations are enclosed and gasketed.
Class II, Division 1 locations (NEC Section 500-6(a)) are environments where combustible dust is present or where dust may produce a combustible mixture under normal operating conditions, or where equipment breakdown may produce such a mixture. The NEC establishes a maximum limit on volt-amperage and size of lamp for these locations. The fixture must be dust-ignition-proof and approved for use.
Class II, Division 2 locations (NEC Section 500-6(b)) are environments where combustible dust is not produced during normal operation but may result from breakdown or other possible abnormal conditions. Fixtures designed for approved use in Class II, Division 2 locations are tightly enclosed and gasketed to prevent escape of arcs or sparks.
Class III, Division 1 locations (NEC Section 500-7(a)) are environments where combustible fibers are produced by normal operating conditions. Fixtures designed for approved use in Class III, Division 1 locations are tightly enclosed and gasketed to prevent escape of arcs or sparks.
Class III, Division 2 locations (NEC Section 500-7(b)) are environments where combustible fibers are handled or stored. Fixtures designed for approved use in Class III, Division 2 locations are tightly enclosed and gasketed to prevent escape of arcs or sparks.
Areas That Experience Abnormal Temperatures
The starting and operation of fluorescent and high-intensity discharge (HID) lighting systems can be affected by abnormal temperatures.
In low-temperature environments such as refrigerated areas, fluorescent lamps can experience adverse performance such as "fluttering," reduced light output and difficulty starting by the ballast. In such applications, enclosed fixtures, special "cold weather" fluorescent lamps and/or jacketed lamps can help ensure reliable performance; in addition, fixtures can be located a suitable distance from cold-air source units. Cold weather ballasts that can start the lamps at temperatures below 0°F should be specified for applications where the ambient temperature is expected to be below 50°F. Cold weather electronic and magnetic ballasts can be specified for HO and VHO lamps that can start them at temperatures as low as -20°F. See the Table below for minimum starting temperatures for a variety of fluorescent ballasts. HID lamps can start in a wide range of ambient temperatures.
Table. Minimum Starting Temperatures for Typical Fluorescent Ballasts
In areas experiencing high ambient temperatures, the ballast can overheat. Class P ballasts contain a thermal protection device that disconnects the ballast from the power source if it begins to overheat. The ballast then cools until an automatic resetter reconnects it to the power supply. If the overheating is not corrected, the process, called "cycling," will repeat itself. In addition, if the temperatures are high enough, ballast life could be shortened and light output reduced.
Fixtures in areas experiencing high ambient temperatures should be well-ventilated. In such fixtures, the heat produced by the lamps generates convection currents that remove the heat. Special HID ballasts can be specified that are designed to operate under high ambient temperatures, or the ballast can be located at a remote location (the distance subject to limitations).
Areas That Experience Momentary Power Failures
In some industrial environments, momentary power failures can cause HID lamps to shut off; they must then cool down before restrike, which can take about a minute for high pressure sodium lamps and as long as 20 minutes for metal halide lamps.
In such environments, HID fixtures can be specified that include a built-in incandescent or halogen lamp that lights when a power failure occurs. Another option is to specify instant-restrike high pressure sodium lamps, which contain two arc tubes. When a momentary power failure or voltage dip occurs, the lighted arc tube goes out and when power returns, the other tube, already "cool," lights, providing some light output immediately and reaching full light output within minutes (see Table below).
Table. Instant-restrike HPS lamp performance. Source: Osram Sylvania, Inc.
To provide for the event that the power failure is long in duration, select fixtures of banks of fixtures should be connected to a standby generator so as to continue critical operations. The number of lamps and their type depends on the minimum light levels required by code. They must provide sufficient light levels for a time period also required by code, usually 90 minutes. Batteries should be checked periodically as required.
Clean rooms are spaces where temperature, humidity, pressure and atmospheric particulates are tightly controlled; the requirements for cleanliness can exceed those for a hospital operating room. Air-handling recessed fixtures may be required that provide either air supply, air return or both.
Light Guides ©2012 inter.Light, Inc. All Rights Reserved. Disclaimer