Dimmable fluorescent ballast ?

[Part 77]

Ran across something new (to me). The ADVANCE dimming ballasts (for F40T12 RS lamps) I was given to install show "circuit interrupting lampholders" in the schematic. I am wondering what their purpose is. The old fixtures these are for didn't have them IIRC. Thanks.

 

[mdshunk]

Some of the 2' strips have circuit interrupting lampholders. They're pretty hard to come by for replacements, in my experience. The one lamp contact wiper in the one side of the lampholder end will flex over when a lamp is installed and touch another metal piece and complete the circuit. Normally the neutral is broken. This is to stop a ballast from trying to light an empty lampholder.

 

[Part 77]

Thanks for the quick response! Yes, they are in the neutral circuit. It may be simpler to order whole new troughers and be done with it. This is the second attempt for our planner to get the parts I asked for.

 

[mdshunk]

Thanks for the quick response! Yes, they are in the neutral circuit. It may be simpler to order whole new troughers and be done with it. This is the second attempt for our planner to get the parts I asked for.

I'm betting those dimming ballasts probably give the lamps quite a jolt to get them up and running if the dimmer is in a lower setting. This might be the reason for the circuit interrupting lampholder requirement. A safety thing, in case a lamp is missing. I think the fixtures I normally see circuit interrupting lampholders in are generally the Slimline instant-start one's. Instant start ballasts have a pretty high open circuit voltage if I'm remembering right.