Although Bodine describes its ARC Keeper 400W backup ballast as an alternative to quartz restrike systems for facilities that depend on metal halide (MH) light sources, Ron Arnold sees it a little differently. For years, the vice president of the electrical department at the Kuhlmann Design Group in St. Louis had settled for specifying supplemental light fixtures — not quartz restrike systems — to supply emergency lighting systems in consumer-driven facilities like grocery stores and casinos, all the while looking for something more economical. “I've been working on this for five years, just trying to come up with an idea to keep the highbays up long enough for a metal halide,” he says.

It's not difficult to tell why he's put so much effort into the search. Any interruption in the power supply — or even a serious voltage dip for a half cycle — will cause an MH lamp to lose arc conduction, and it could take as many as 15 minutes before the arc can restrike even when a backup generator is up and running, which is a far cry from the 10-second requirement in Art. 700 of the NEC.

It was possible for Arnold to work around those shortcomings by adding as many as 16 supplemental floodlights to his designs, but it ultimately raised the cost of installation. “I've always thought it would be nice if they could get a ballast that would keep a 250W or 400W MH on long enough for a generator to pick it up,” Arnold says. “Lo and behold, now they have.”

Think of the ARC Keeper as a UPS for MH lighting systems. Built upon a Ni-cad battery, the ballast tracks the line that feeds the fixture and will jump in and operate the lamp within 2 milliseconds of detecting any interruption to that line that falls outside of a range of acceptable wave shapes. For the next two minutes, or until the facility's generator can get up and running, it will maintain lamp power at 25% of rated power. And although that's a significant reduction, it's better than the alternative. “There's a safety factor involved,” says John Levesque, the national sales manager for Bodine. “Imagine a gymnasium full of students. If you have a power flicker or failure, you're basically without light until the generator powers up.”

Other technologies exist for compensating for the long restrike time of MHs — namely quartz restrike systems — but Levesque says they don't really compare in terms of luminance or functionality. In the event of a power failure, an area that relies upon a quartz restrike system for emergency lighting will be without light until the generator responds. Once the generator is running, a 250W quartz lamp will operate at about 6,000 lumens to 7,000 lumens until the MH lamp restrikes, but the change in supply after normal power is restored will cause the MH lamps to lose arc conduction again. By comparison, the ARC Keeper ballast will provide reduced illuminance for only the time it takes the generator to power up and will then allow the MH lamp to operate at full light output immediately thereafter.

Arnold never subscribed to the theory of using quartz restrike systems for emergency lighting, but it's a moot point for him now. Now that he can eliminate the additional floodlights and the extra relay that went with them, he's saving his customers as much as 30%. “Now I can maintain the full light level of the fixture because I can put it on an emergency generator and keep it going,” he says. “Where I had supplemental lighting before just for emergency situations, now I'm just using the existing lighting and the Bodine ballast.”

Product Specs
Arc maintenance time 2 min continuous
Electrical supply 120/277V (50 Hz/60 Hz)
Temperature rating 0°C to 55°C
Dimensions 12.25 in. × 7.25 in. × 1.75 in.
AC input current 0.8A
AC input power in standby mode 6W at 120V and 10W at 277V
Power to lamp arc during maintenance operation About 25% of normal operation power

For more information, visit www.bodine.com.