In his December “Product Safety” column in LD+A, Jerry Plank discusses how LED driver substitution continues to be hampered by a lack of standards. An excerpt follows here.
The great Yogi Berra recently passed away, but his quote “If you don’t know where you are going, you’ll end up someplace else” is apropos to the situation surrounding LED drivers. Why? The integration of controls in buildings places a larger burden on lighting manufacturers and designers, as lighting specifications often detail the driver to be used on a project, which is compatible with the lighting controls.
Sounds simple on the surface, however, due to the market demands and technical differences, a lighting manufacturer cannot, on a practical level, have the luminaire tested by an NRTL (Nationally Recognized Testing Laboratory) to include all possible drivers that may or could be used in the future. Adding to the dilemma of driver substitution is the fact that LED driver technology is changing quickly and driver manufacturers are adding and discontinuing models at an alarming rate.
So how did our industry get to the point where LED driver substitution has become a nightmare? Simply put, industry and standards-making bodies did not know where our industry was headed.
There was a time when coordination of components between industry and the NRTLs was forward-looking, as was the case for linear fluorescent lamp ballasts. In the 1960s, electrical fires due to fluorescent lamp ballasts failing in the field were common. The cause of the field fires in early fluorescent lamp ballasts was that the potting compound used in the early metal cased ballast was bituminous material, better known as asphalt, which caught fire when the insulation system in the ballast failed.
The solution for preventing electrical fires was the creation of the Class P fluorescent ballast, where every linear fluorescent lamp ballast incorporated a resettable thermal device, which deactivated the coils when a short in the insulation system occurred. In addition, the ballast case sizes and mounting feet were standardized among all ballast manufacturers to facilitate easy replacement in the field and factory. Replacing a failed LED driver in the field today would not be as simple from an electrical or mechanical point of view.
The key element that allowed a Class P ballast to be interchangeable with any other manufacturer’s Class P ballast was the use of standardized electrical parameters through the ANSI process and the fact that the NRTL Listed the Class P ballast. The NRTL and industry agreed that 90 deg C would be the maximum temperature before the thermal device operated and prevented overheating and a possible fire.
Making it more challenging for LED drivers from one manufacturer to be easily substituted for those from another is the fact that most LED drivers are component-recognized by NRTLs and as such, the maximum operating temperatures are not standardized, nor are the drivers required to be thermally protected. Further, industry has not standardized, as of today, electrical parameters on the drivers or the arrays for that matter.
Some NRTLs have initiated driver substitution programs such as UL’s TL program, however, the program does not have standardized limits, which makes it difficult, if not impossible, to substitute drivers between manufacturers. The biggest problem with the program stems from temperature limits and electrical parameters that are difficult to cross-reference. Until our industry agrees to ANSI ratings for LED driver products, drivers will not be easily cross-referenced and the TL program of UL will be limited. Other NRTLs have evaluation programs comparing various drivers with each other, but the evaluation is on a case-by-case basis.
To solve the LED driver substitution conundrum, the industry and the NRTLs must work towards ANSI standard ratings and address key elements such as:
- Standard case sizes of drivers and a common location of mounting holes to facilitate field replacement.
- Standardize the location and type of wires used on the input and output ports.
- Standardize electrical connectors (supply connection) used, if any, on the input and output ports.
- Circuitry that is compatible with all lighting controls, like DMX protocol used in stage lighting.
- Always having the NRTL investigation of a driver lead to a maximum case temperature rather than ambiguous ambient temperatures that are meaningless.
The items suggested above are a start and certainly not a definitive list. Once the lighting and driver industries can agree on common terms, LED driver substitutions will be easier to make in the factory or the field.