Knob and tubing

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ronaldrc

Senior Member
Location
Tennessee
Just for curiosity what do most of you think is more of a fire hazard?

With a ceiling mounted light fixture with two 60 watt incandescent bulbs and the bulbs are no more than a few inches below the ceilings surface.

1. Two knob and tube wires coming from over the light fixture through two holes separated by about two inches of ceiling material and no box?

2. Three pieces of 12/2 romex two hots and one switch leg in a metal ceiling box?

3. Three pieces of 12/2 romex two hots and one switch leg in a plastic ceiling box?

I don't have the answer I just want to have opinions of others.

My first opinion without giving it a lot of thought is #3 with a plastic box.Reasons being with the metal box the hot wire will more and likely short out and kick the breaker or blow a fuse as intended.

With the knob and tubing chanches of it shorting are almost impossible.

But with the plastic box with the wires cooked and close togather as with romex and carbonized could very easily set there and turn cherry red and never kick a breaker before starting a fire.

Whats your opinions on this?

Ronald :)
 

hurk27

Senior Member
Re: Knob and tubing

It would be a close run between the knob and tubing and the plastic ceiling box. but I thought that carbonization is when a bare hot wire comes into contact with a wood product and over time it slowly carbonized the wood to the point that it causes a flash over and puff you have a fire. but I can under stand the insulation being heat dried to the point that it cracks off the wire but it usely comes off when someone has to work on the light, I havent seen this with fans that much unless there used to be a light there and the person who installed the fan didn't repair the wires. the biggest problem is homeowners that over wattage there fixtures. and this is a big problem because they dont know the light output when they select fixtures. but with the knob and tubing the other type of carbonization of wood is possable if there is any hots touching the wood as it might not be a short now it will be a flash over later.
 

ronaldrc

Senior Member
Location
Tennessee
Re: Knob and tubing

The reason I didn't pick the knob and tubing is because there is usually just two wires coming to the light from the ceiling.Your switch leg is usually tied in attic above the switch not in all but most cases.

You usually have four or five taps made in the ceiling box with romex.As far as the composition of the wires and if the insulation turns into a flamable substance when it burns or chars I hope will be answered by someone familiar with that.

Ronald
 
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