3 lamp ballast question

[DanZ]

I had an odd question from an engineer the other day, and I couldn't answer it. In a 3 lamp linear fluorescent light fixture, with a single ballast, can you remove a lamp to make it a "2 lamp fixture" and still have it work?

 

[roger3829]

If it's an electronic ballast it will work. They work no matter how many lamps are installed.

 

[DanZ]

Thanks! That's what I thought.

 

[Mike01]

??

??

I believe as long as the ballast is a "parallel" wired that is correct however if it is a "series" ballast the loss or removal of one lamps and the fixture no longer operates.

 

[LarryFine]

can you remove a lamp to make it a "2 lamp fixture" and still have it work?

This should be indicated on the ballast label or accompanying documentation.

 

[DanZ]

This should be indicated on the ballast label or accompanying documentation.

Really? I didn't know that! These were existing light fixtures that the tenant wanted to reuse, and the engineer was a little worried when I said we could just take a lamp out and make them a "2 lamp fixture" to pass energy code.:wink:

 

[Bigrig]

If you are talking about the ASHRAE 90.1 energy code please remember the wattage calculations would be based on how many watts the ballast uses, not just the lamps. I am not sure what effect removing a lamp would have on ballast draw.

 

[DanZ]

If you are talking about the ASHRAE 90.1 energy code please remember the wattage calculations would be based on how many watts the ballast uses, not just the lamps. I am not sure what effect removing a lamp would have on ballast draw.

I know, I know. It should reflect the maximum allowed wattage of the fixture, not what I put in it. But I haven't had any complaints yet!:wink:

Most Plans Examiners are okay with specing incandescent can lights and CFL Lamps, using the CFL wattage for the allowed wattage.

Besides, removing a lamp from a fixture to get it's wattage down is a whole lot better than suggesting a tenant cut a linear fluorescent fixture in half so it will fit in a 3' grid! Dang'd Appalachian Architects!:wink:

 

[lbernard]

Tandem wiring of fluorescents

Tandem wiring of fluorescents

When wiring fluorescent fixtures in tandem (master/slave) does the whip to the slave fixture have to maintain the ballast wire color?

 

[DanZ]

When wiring fluorescent fixtures in tandem (master/slave) does the whip to the slave fixture have to maintain the ballast wire color?

Well, I don't believe there's anything in the code requiring wires to have specific colors, so I don't think you actually need to. Although changing wire color in the middle of a run seems like a bad idea to me.

 

[lbernard]

the problem is that the whips (13,000) all came from the factory with blue wires. The ballast manufacturer specifies that in tandem wiring, the blue ballast wires must remain in the fixture with the ballast.

 

[Smart $]

the problem is that the whips (13,000) all came from the factory with blue wires. The ballast manufacturer specifies that in tandem wiring, the blue ballast wires must remain in the fixture with the ballast.

You need to be asking the manufacturer this question... and if they acknowledged the contradiction, saying it is ok for blue wires to exit to the slave fixture, request their resolution in document form!

 

[broadgage]

To return to the originall question as to whether or not a multilamp ballast will work with one or more lamps removed, there is no simple answer, it depends on the ballast.
The only reliable answer is to try it and see, or ask the manufacturer.

In the case of older magnetic ballasts it again depends on the internal circuitry, and only enquiry or a test will answer the question.

 

[DanZ]

Thanks guys! I was thinking it would be a case by case thing.

As to the other question, I agree go to the manufacturer and see what they say. If they say it's okay, get it in writing.