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Joined: Oct 2000
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This happened a few months ago. A one-way bulb in a three-way socket and a short circuit inside the socket tripped the breaker switch; the bulb was a mini-fluorescent bulb.

The one thing I find odd is that I have a lamp with a three-way socket and have used one-way fluorescent and incandescent bulbs in it for years and as far as I can remember, there’s never been a problem with that.

I included a shot of the sticker saying the max wattage the lamps rated for.

- Tristan S.

[Linked Image from]

[Linked Image from]

Joined: Apr 2002
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Bad ballast in the CFL lamp??

Joined: Mar 2008
Posts: 76
Not sure John, I don't think so because it was the second hot treminal and the side treminal that had the arc fault. I didn't notice any signs that would have indicated a problem but maybe there weren't any signs to notice. The copper terminal that's dead center didn't have any signs of arc fault damage so I'm thinking that the arc fault resulted when the second hot terminal became live when its switch contacts closed as the switch knob was turned. I planning on checking for other damage that may have been caused when this happened just as a precaution.

Last edited by packrat56; 02/22/09 12:55 AM.

I have a sense of adventure, I just keep it leashed with common sense.
Joined: Mar 2007
Posts: 404
What does the base of the bulb look like? Perhaps it wasn't machined right, and had a larger area on the screw or tip, causing the short?

Joined: Jan 2006
Posts: 558
I see what looks like shiny melted copper on the right side of the terminal in question and the metal screw shell of the socket. Perhaps there was some metallic "spare part" that fell into the socket or made its way between the terminal and screw shell when the bulb was changed out?


Joined: Dec 2005
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The answer is the three words that begin with "Made" at the bottom of the label.

Joined: Nov 2002
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Originally Posted by Rewired
Perhaps there was some metallic "spare part" that fell into the socket or made its way between the terminal and screw shell when the bulb was changed out?

Reminds me of some stupid pranks some kids in my college dorm used to do to the wall sconces in the stairwells. Those had light bulb sockets facing up, no enclosure around the bulb. Someone would steal the bulb to replace a blown bulb in their desk lamp, and someone else would drop a penny into the empty but live sconce socket. And cause sparks and trip the breaker... idiots.

Joined: Sep 2005
Posts: 97
Why is there a cardboard tube around it?

Perhaps that is where the risk of fire lies wink

Interesting as we dont have this sort of three way fitting in the UK.

I took my time, I hurried up, The choice was mine, I didn't think enough
Joined: Apr 2002
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Lamp sockets come with a 'cardboard' sleeve here in US; sleeve promarily is the 'insulator' from the hot/neutral screw terminals on the side of the socket, to the metalic outer shell (sometimes brass finished) We also have other configarations. There is also a lot of 'junk' as Ann was leading to above.

The interior of the socket is wired screwshell is neutral, center tab is 'hot', secondary tab is for 3 level lamps. 1 'on' is low wattage; 2 'on' is med. wattage; 1 & 2 "on" is 'high' wattage.

Joined: Dec 2001
Posts: 2,498
3-way bulbs are obviously a particular US thing.

European Edison base sockets are built differently, they don't have live threads, instead they're built with two bottom terminals. The actual thread is isolated from the shell by a plastic ring. Never seen one of those fail, the only typical problem: overheated cord, PVC gases out creating acidic smoke, terminals corrode.
Here's a pic:
[Linked Image from]

The outer shell is also considerably sturdier than its US counterpart.

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