knob and tube wiring

[tracer]

I have an older home (1904), in a covered porch area there
is a light. As I am about to put some insulation in this area I was viewing the knob & wire--which is in great shape---but I had read somewhere that you should protect the fixture area from the insulation being directly on it, with a cone or tube. Correct?

It also appears that there is only one (a single) wire running to this fixture, comes out of one wall goes to the fixture and then back into another wall with the wire being attached to each side of the light fixture.....is this just a loop with the hot wire being attached one end of the light switch and the light just being part of the loop?....only one wire going in to the light and one wire going out. ( thought there had to be at least a ground and a hot)? thanks for your help.

[Wgoodrich]

Knob and tube wiring is an older style wiring system although it is still recognized today in the NEC for new installation I know of no one that uses this knob and tube style wiring anymore in new installation exept for branch circuit extensions from existing wiring.

The single wire in and single wire out is normal knob and tube wiring style and is without an equipment grounding conductor. This without and equipment grounding conductor is allowed as existing because it was approved at the original wiring style installation at the time it was installed. If you install new wiring then the equipment grounding conductor would have to be included in your new installation.

Be aware that it is against the NEC rules to bury knob and tube wiring in insulation. If you plan on insulating your house you need to plan to rewire you entire house. Knob and tube wiring is not allowed to be in insulated walls or otherwise buried in insulataion.

The cone you are thinking of is required to be installed only on recessed style light fixtures that are not approved for in contact with combusable materials. This cone or chemney is designed to allow heat to disappate from a non-incontact approved recessed light fixture only.

This cone or chemney is not required and does not apply to any surface mounted light fixture. There is a peice of insulation that is found inside the code of a surface mounted light fixture most commonly. This insulation is installed within the mounting cone of your surface mounted light fixtures by your manufacturer and is designed to insulate the conductors in the box above that light fixture from the heat produced by that light fixture.

Hope this helps

Wg

[Breckrider]

Ooooops.....apparently nobody told the previous owner of my house that. I have a mix of knob and tube and conventional wiring with blown insulation everywhere. When I bought the house it was inspected and nobody said anything about it. ANything I should be worried about?

[Wgoodrich]

Your house is not the only OOPS ! in the country. Many insulating companies and home owners have insulated over knob and tube wiring in hollow spaces violating the NEC rules. Many homes in the country are also with knob and tube wiring that is buried in insulation. It is definite that your home is in violation of the minimum safety standards.

I am going to let you make this judgement how unsafe you may be.

Below is a copied section of the NEC 2002 containing that rule relating to this subject. Also there is an NEC Handbook commentary directly following that rule of the NEC.

394.12 Uses Not Permitted.
Concealed knob-and-tube wiring shall not be used in the following:
(5) Hollow spaces of walls, ceilings, and attics where such spaces are insulated by loose, rolled, or foamed-in-place insulating material that envelops the conductors

COPIED SECTION OF THE NEC 2002 HANDBOOK COMMENTARY;
Concealed knob-and-tube wiring is designed for use in hollow spaces of walls, ceilings, and attics and utilizes the free air in such spaces for heat dissipation. Weatherization of hollow spaces by blown-in, foamed-in, or rolled insulation prevents the dissipation of heat into the free air space. This will result in higher conductor temperature, which could cause insulation breakdown and possible ignition of the insulation.

At this point I am going to let you make the call on your own home.

Hope this helps

Wg

[Breckrider]

Ouch.......well merry christmas

[Wgoodrich]

In this case while knowing the facts may cause you to yell ouch, it is better than to never have known until you welled smoke !

At least now you are aware of this rule and can make an informded decision what you need to do about it in your mind.

At least you asked, just think how many out there have no idea of this concerning subject.

Good Luck

Wg