Explosion Proof Lights and Hot Environments|
Article - February 23, 2016 By LarsonElectronics.com
Explosion Proof Lights and Hot Environments
Fixtures that are exposed to high ambient temperatures are prone to failure and malfunction. In industrial facilities with high lighting consumption rates, this is can be a complex issue to address, especially in hazardous locations where explosive dust and vapors are present. As a solution, establishments may apply explosion proof metal halide and incandescent fixtures with external ballasts.
Electrical ballasts are designed to monitor and limit the amount of current in a circuit. The two most common types of ballasts include electromagnetic and electronic. In industrial lighting systems, such devices provide optimal conditions for the fixture to start and operate. It is common for both components (lamps and ballasts) to be matched electrically (wattage, length and diameter) to ensure compatibility. Without a ballast, a lamp would be open to premature failure due to exposure to high voltages from the power source, causing it to overheat and burn out.
When turning on a light, the device initially pushes out high voltage needed to create an arc between two electrodes, or the electrical terminals found at the ends of electric discharge lamps. The ballast regulates the voltage to a lower setting once the arc has been established, and continues to supply steady current to ensure light output. It is important to consider that a switch is required to turn the fixture on/off and the ballast does not provide this function.
Optimal Operating Temperatures
During operation, ballasts generate heat (like any other electrical device out in the market today). Because of this, businesses must take external, internal and operating temperatures into consideration during lighting installation. Maximum heat dissipation must be carefully planned during design and ballast selection. Additionally, the units must be protected from moisture, weather and abnormal external conditions. Exceeding temperature thresholds can decrease the lifespan of the device and the lamp to the point of failure- though it is common for ballasts to require replacement and maintenance when used on a regular basis. For example, weatherproof ballasts have a maximum case temperature of 90 degrees Celsius, where below this threshold it can operate normally. Exposure to temperatures above +10 degrees Celsius of the ballast’s threshold may decrease its lifespan by 50 percent.
Low temperatures are also not ideal for ballast operation. This is because cold environments decrease the availability of vaporized gas within the arc tube of the lamp. As a result, the voltage requirements needed to create the arc increases to a point where the fixture will not start. Cold temperatures may also prolong a light’s warm-up period. Such events are easily avoidable by checking the minimum (or maximum for hot environments) temperature settings of the unit- usually listed on the label or technical specifications of the lamp.
External Ballasts and Hazardous Locations
Businesses may choose lamps with internal or external ballasts, depending on the needs of the facility. Internal ballasts are more common for mainstream applications and are more prone to failure compared to its external counterpart. This is because bulbs that rely on internal ballasts have a tendency to get extremely hot; and the fragile filaments break when the light is tampered during operation. Fixtures with external ballasts are sturdier by design and have a longer lifespan. Such units do not give off as much heat, which allows the filaments to maintain a cooler operating temperature. Moreover, external ballasts can be used in tighter enclosures due to its low heat output properties.
External ballasts may be applied in hazardous locations and hot environments. In such settings, the air may contain combustible dust and vapors that may ignite when in contact with electrical equipment. Under such circumstances, the fixture, wirings and controls must adhere to guidelines set forth in Section 500 of the NEC.
In hot environments, ballasts are at risk of overheating because they are a major heat source. It is best practice to rely on external ballasts to reduce reliance on ventilation, coolers and fans. Class P ballasts (the UL classification for thermally protected ballast) automatically disconnects from the power source when overheating. The device cools down and reconnects to the power supply through a resetter. The process repeats itself until the issue is corrected (called cycling). Lastly, to ensure functionality in hot environments, the area should also be well ventilated.