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Knob and Tube Wiring

What Is It?

The old wiring system, that was used up into around 1950 , depending on what area you are in, is what is known as “ knob and tube “ wiring.Where the “ tube “ is a ceramic tube, that was installed in the holes that where drilled in the wood, that would act as a protection, when the wire was pulled through it. The “ knob “ was a ceramic knob, with 2 parts, ( sometimes known as “ split knob and tube “ ), the wire would be secured inside the split knob, and then a nail or screw installed to hold it in place. The wire was a single conductor , with a type of Fabric insulation. They had mainly white, ( neutral ), and black, ( hot ) colours, i have seen it in red also. If for example, when they ran it in the attic, they would secure it, one line on each side of a joist space, facing each other, if the joists were @ 16” centres, then you had that extra “ insulation” between the 2 wires.

Usually there were no boxes used in the attic part of the system, one line would be wrapped around another line, or they would make a junction point, and twist a few together ,and then solder them, and then wrap with fabric tape. The outlet boxes, and switches, would have a metal box, most times screwed on the  “Lath and Plaster “ finish, or the outlets would be mounted,     sideways , right into the large molding, at the base of the floor. The Lights in the ceiling, usually had a “ header “ piece of wood mounted between 2 of the joists, and the 2 holes drilled in the wood, the wires would pass through the holes, with some extra wire protection, known as “ loom “.
Because this was just a 2 wire system, there was not a grounding system.

Why are insurance company’s saying i cant have, or have this wiring checked?

In all my experience re-wiring homes, it is always the same classic scenarios that pop up.

  1. The Knob and Tube has been tampered with, with someone maybe “ adding “ some more wiring, to power up extra lights / outlets etc. Because there was no junction boxes used in the attic, there was not a point to “ go into” the system. So most times, the wire insulation was just scrapped off, and the new wire wrapped around it. Sometimes i have at least seen some electrical tape wrapped around it, but rarely soldered, ( how many handyman even own a soldering gun )?
  2. When it was the Knob and tube era, there was not many appliances in the household, you had plug in lamps, Fridge, maybe a toaster, and then later a washing machine. So the houses did not have all the outlets / circuits installed like today. So what happens when there is no outlet in a room? Out comes the extension cords, and i have seen some very creative extension cord installations over the years! Most people have heard by now, this is not the best way to wire a house, especially using the cheap dollar store variety.
  3. Also when it was the knob and tube era, the Main Electrical Service to the house, usually was a 60 amp Service, because you did not have all these appliances like today.
  4. The Knob and tube wiring was not designed to be installed in insulated ceiling and walls, or be installed into recessed Lighting ( pot light ). Pot lights need a 90 C rating on the wire supplying them. I have been in attics, where it was so hot, (poorly vented ), there was hardly any insulation left on the old knob and tube wiring.
  5. With some simple research on the internet, i found out a house that old, may have had 5 to 8 renovations done to it, mainly Kitchens and Bathrooms topping the list. So what are the odds, that the knob and tube wiring has not been compromised in some way.
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