New Lights & 90 Degree Rated Wiring


Old 01-16-01, 10:40 AM
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Help! I want to replace some old ceiling lights with new ones which use 2 standard 75 watt light bulbs. However, the instructions warns that the wiring needs to be rated at 90 degrees C. I have the old knob and tube stuff which definitely does not meet the 90 C rating.

What should I do? Should I replace a length of the knob & tube wiring, and if I should, how much of wiring (in feet) should I replace? (I don't have the resources to replace all of the old knob & tube wiring in the house.)

If I need to replace some of the wiring, what is the best way to replace it? Should I simply join the old wires and the new wires in a junction box?

Also, one of the lights is mounted in a place where the wires are not easily accessable. Should I just use the old wiring in that case?

Thanks for your help!
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Old 01-17-01, 02:38 PM
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First test the knob and tube wiring to be in good condition.

Turn off your breaker. Then take your first and second fingers and spread then wide, now take your thumb and bend the wire sharply with your thumb between your two fingers. This method of bending your wire insures that you make a sharp bend. If the knob and tube wiring bends and then bends back to being straight and no insulation pops off or cracks during the bending and straightening then this wire has not been over heated. If the wire is pliable then you can proceed to the new installation of your flourescent fixtures as follows. Wire nut a piece of new romex in the light fixture box and extend this Romex into the flourescent fixture and wire nut the fixture wires to the new Romex. The wires in a new Romex is rated 90 degrees C and fulfills the recommendations of the manufacturer. The knob and tube wiring didn't enter the fixture but the new extension made of new Romex did and it is 90 degree rated.

If you find the insulation to be damaged due to heat and the insulation cracks or pops off during the bending test then go into the attic and follow the wire back to where it is still pliable, cut it in two and throw away the damaged section of wire. Now install a junction box in an accessible area but not to be covered by insulation and place the older cut wires that is still good in the junction box, then extend your knob and tube wire to the light box where your flourescent light is located and enter the flourescent fixture and wire nut the wires the same as the old fixture was wire leaving this splice inside the area with the ballast of the flourescent fixture. New Romex made today and UL listed is rated 90 degrees C Which meets the requirement of the flourescent fixture manufacturer's recommendations.

Hope this helps

Old 01-18-01, 09:04 AM
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Thumbs up Thanks for Reply; Follow up question


Thanks for your reply! It really helped. A follow-up question -- If the knob & tube wiring is good, how long of a Romex cable should I use to extend the wire from the lamp fixture box?

Again, thanks for your help!
Old 01-18-01, 12:22 PM
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Only as long as needed. Do not run your knob and tube wiring into the flourescent fixture. Use the new wires to enter the fixture. The NEC requires that you have 6" tails in each junction, receptacle, switch box to work with.

Good Luck

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