SignIndustry.com
Despite sizes up to 20 pounds, sign ballasts operate on the same technology as any other ballast and perform the same three functions: to facilitate starting, to operate the lamp, and to limit electrical current to proper levels. However, they require specialized UL designations and unique selection criteria.
Every sign ballast has a number of symbols and notations on its label to indicate that it meets certain industry requirements as established by Underwriters Laboratories (UL). For example, ballasts labeled as class “P” will automatically disconnect from the supply line if the internal temperature of the ballast coils reaches 105 degrees centigrade. The ballast will automatically reconnect when it cools down.
Sign ballasts are generally manufactured using “UL Type 2 Outdoor” cans, which has a special coating to resist rust so it can used in plastic sign applications without a separate metal enclosure. While a “Type 2” can is not weatherproof, it does provide some moisture resistance.
Another common UL marking is “HL” for hazardous locations, meaning there are no sparking components exposed to the air. “HL” is a typical requirement in the petroleum industry. All Signa ballasts are UL class P, Type 2, and HL listed.
Ballast Selection
Choosing the right ballast for a plastic sign application is a relatively easy task. Typically, sign ballasts are rated for 120 volt input and operate 800 mA high output (HO) T12 lamps, although sign ballasts are also available for slim-line lamps or other voltages, such as 277.
Lamps are generally operated in series (six-lamp ballasts are two three-lamp series circuits, in parallel) so that lamps are part of the circuit—meaning that if one lamp fails, none of the lamps on that circuit remain lit. In signs using multiple ballasts, adjacent lamps will often be operated by different ballasts to avoid a large dark spot should one lamp fail.
To select the proper ballast, the most important variables are the number of lamps and the total lamp footage. For example, Signa sign ballast 256-448-800 will operate any 1-, 2-, 3- or 4-lamp combination of T12 800 mA lamps covering 8 (minimum) to 16 feet (maximum) in total lamp footage.
Sign ballasts have wide application ranges that often overlap. For example, Signa offers five different ballasts that operate two four-foot lamps. As a general rule, the most economical choice is to choose the ballast where the actual application is as close to the maximum limits of the ballast without going over. For example, a ballast for one or two-lamps is generally less expensive than a ballast for one-, two-, three- or four-lamps, and a ballast that operates up to 16 feet maximum is less expensive than one that operates up to 24 feet.
On the other hand, the lowest cost ballast option may not always be the most practical. Using sign ballasts that operate many applications can simplify inventory needs and reduce costs. As long as the actual application is within the ballast’s published range, you can be confident with its performance.
If a lamp application is listed on the ballast label, then it has met and passed all of the UL testing requirements. Otherwise, it should not be used in that particular application. Ballast overheating, excessive lamp end blackening, hard starting, short lamp life or short ballast life are a few of the possible field problems caused by using a ballast that is not rated for the application. The UL coverage will be voided by using a non-listed combination of lamps. Typical service calls for a plastic sign cost several hundred dollars. Saving a few dollars by using a “close enough” ballast is not wise in the long run.
Ballast Performance
Temperature is a critical factor in the performance of a sign. Light output is a factor of the mercury vapor pressure inside the bulb. The colder the lamp is, the lower the light output. Cold lamps are also more difficult to start. Magnetic sign ballasts are rated for reliable starting down to -20 degrees Fahrenheit. At temperatures below that, it can be difficult to start the lamps.
Another factor is a poor ground, which can cause erratic starting. More importantly, grounding provides added safety. Although sign ballasts are designed under UL standards for protection from shock hazard, certain conditions of ballast failure at end-of-life can result in shorts. An ungrounded sign is a potential hazard and can give misleading symptoms when looking for sign faults. Always disconnect the power before servicing a sign. Service work should only be performed by qualified personnel and in compliance with OSHA guidelines for safe electrical practices.
The two main enemies of the ballast are heat and moisture. A ballast will generate heat during operation and by design should not exceed 90 degrees centigrade at the hottest spot on the ballast case. Higher operating temperatures will shorten the ballast life and could result in thermal cycling. To maintain normal operating temperatures, the ballast should be mounted against a flat surface of heavy gauge metal, such as a structural part of the sign, and it should be mounted far away from other sources of heat, such as other ballasts and lamps. A lamp will generate about three-fourths of the heat in a plastic sign. The ends of the lamp are the hottest part, so the ballast should be mounted as far away from the lamp ends as possible. To help reduce moisture the sign should be well vented without allowing water to enter.
High or low line voltage can have a major impact on the life of the sign components. Low voltage does not generally impact a ballast life, yet it can result in inadequate filament heating during starting, shortening lamp life. High line voltage can result in shortened life for both the ballast and the lamps. Signa recommends that corrective measures be taken if the voltage is less than 110 or higher than 125 on a nominal 120 volt circuit.
Editor’s note:
Please forward all reader inquiries to:
Universal Lighting Technologies Inc.
Marketing Communications Manager
26 Century Blvd. Suite 500
Nashville, Tenn. 37214-3683
1-800-BALLAST
www.unvlt.com
webmaster@unvlt.com