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Can you safely use a 3-way bulb (50-100-150W) for a lamp that accepts a 100W bulb maximum? Is there any fire hazard involved?

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Is it a three way fixture? –  bib Jan 13 '14 at 0:55
    
No, it isn't. The fixture is meant for a regular bulb. –  THE DOCTOR Jan 13 '14 at 1:01

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No.

A three way bulb has two separate filaments that are lit separately by two separate contacts on the bottom of the bulb. The three way socket allows each of these filaments to be lit separately or together.

A 50-100-150 watt bulb has a 50 watt filament and a 100 watt filament. It draws 150 watts only when both filaments are lit at the same time.

If you put a three way bulb in a conventional socket, only the center contact will be lit. In your case, that would be the 100 watt filament. This does not exceed the max rating and you are fine.

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That was very informative, thank you. I put the light bulb in, flipped the switch, and it didn't explode in a ball of flame so I guess I'm good. –  THE DOCTOR Jan 13 '14 at 2:01
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While it's true that only the center contact should be live, since this fixture was not designed for a 3 way bulb, it's possible that the center contact is oversized or off centered enough to contact both of the filament contacts on the bulb. The lack of immediate problem upon turning on the switch is no guarantee of safety - it can take many hours (or even years of continual use) for overheating to cause a problem. Why not just use a standard bulb (or better, a new, energy efficient model)? –  Johnny Jan 20 at 23:27
    
@Johnny You are definitely right in principle, but I have seen scores of one ways put in three ways and vice versa, and never seen a short between the two filaments or the hot an neutral. A low risk situation, I think. But obviously the right thing is to use the right bulb. –  bib Aug 4 at 0:50

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