Is there any standard out there in terms of ranking residential electrical cable options for fire safety, specifically in enclosed and/or insulated spaces?
I've read that old knob & tube is actually very safe, if undamaged, due to the distance between the wires. What about as compared to NM, or armored cable (MC), or NM-in-conduit?
I'm new to this stuff, so I apologize if my terminology/usage is incorrect…
(We have knob & tube in our walls and attic, and I'm wondering if having an electrician replace some of it, in areas where we want various electrical and insulation changes/upgrades, is actually going to reduce fire safety.)
Best Answer
Metal conduit is considered "noncombustible", which means if there's a fire, it shouldn't burn. However, if the wires/cables inside the conduit produce heat, the conduit does nothing to prevent the transfer of that heat (aside from possibly spreading it out). Therefore, it does nothing to prevent fires. Though it may reduce toxic fumes, and will not become a fuel in the event of a fire.
If you're looking to reduce the risk of a fire being started by the electrical system. You should be looking at circuit breakers and other similar devices protecting the wires, not so much the wires themselves.
If you can accurately detect potential fire hazards as they happen, and take steps to reduce and/or eliminate them. The wires themselves don't matter much. Installing and maintaining high quality short-circuit, overload, overcurrent, arc-fault, and ground-fault devices will reduce fire hazards.
If you're really concerned about electrical fires, installing larger wires than are required can help. Larger wires will be able to dissipate more heat, and therefore will be less likely to start a fire (when properly protected). For example, using 12 AWG conductors on 15 ampere circuits, will provide the protection device additional time to respond to a hazard.
Increasing the number of circuits, can reduce the tendency to overload the circuits, thus reducing one fire hazard. If you have a room where a lot of equipment will be plugged in, consider installing two or three general receptacle circuits instead of one.