Metal Halide Lighting Question

This is my guess:

Ballast and lamp are matched. In the ballast mode (after ignition)- the current will not be enough to attain the needed drop - your lamp will have a too high working voltage and die soon.

by explosion or melt down. Whatever comes first.

I must be honest.

This is for a 220 Volts ballast. I don't know what happens on 120 volts (think the working voltage might be around 90 volts)

Ballast voltage is 277, one leg of 480V, 3 phase service.

I am not sure I agree with the guess. Wouldn't the output voltage be fixed? And the current available would vary? I am a bit worried what might happen to the lamps, but do not want to rely on a guess. Thanks for posting though!

Any other answers?

I said I didn't know with a ballast on 120V. But with a 277V- YOU GO STRAIGHT TO DISASTER - AM I CLEAR?

Clear as the broken glass that I was trying to avoid cleaning up in POST #5!!!

I am old enough to be avoiding the type of disasters that were described by you and others. That is why I appreciate forums like this where I (and others) can ask these type of questions.

THANKS ALL! (still don't like the answers, but I will head the advise!)

You will get what is called a "catastrophic" failure with the internal glass envelope failing violently thus causing the outer glass envelope to follow suit.

Ballasts are sized to the lamps. Do not mix and match.

Purchase and install the proper lamp or use a smaller ballast to match smaller lamp. It is not worth getting hurt to save a few dollars or a little time.

What the others have said : your lamp will overheat and fail due to overcurrent, probably by rupturing the arc tube.

If it was ok to do what you are asking, why on earth would the manufacturers go to all that trouble to make a ballast to match each size of lamp?

Remember back in the days when we used flash bulbs on our cameras?

Before knowing too much about MH lamps, I thought I could save our non-profit a bit of electricity by using a 250W lamp in a fixture designed for a 400W lamp. The 250W lamp was also cheaper. I can say that it was not a "catastrophic" failure, the lamp did work for some time, but, it only lasted a couple of months instead of the couple of years we usually get with the properly rated bulb. I don't recall, but I do think I remember that the internal glass envelope was compromised on the "abused" lamp, but the outer envelope was still intact.

I have since learned more about MH fixtures, and won't make that same mistake again. For what it's worth, this particular fixture was operating with 120V input.

Tom D.

Thanks tdesmit! This is my situation, we are trying to use donated 320 watt, 277v light fixtures for lighting in a warehouse to church conversion. I appreciate your sharing the lesson learned!

Ried