What is knob and tube?
It consisted of single-insulated copper conductors run within wall or ceiling cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported along their length on nailed-down porcelain knob insulators. Where conductors entered a wiring device such as a lamp or switch, or were pulled into a wall, they were protected by flexible cloth insulating sleeving called loom.
Knob and tube wiring was eventually displaced from interior wiring systems because of the high cost of installation compared with use of power cables, which combined both power conductors of a circuit in one run (and which later included grounding conductors).
Limitations and dangers of knob and tube:
- usually restricted to a maximum of 60 amp service
- it is not a grounded system making it more hazardous than modern wiring
- permitted the use of in-line splices in walls without a junction box
Knob-and-tube wiring may also be damaged by building renovations. Its cloth and rubber insulation can dry out and turn brittle. It may also be damaged by rodents and careless activities such as hanging objects from wiring running in accessible areas like basements.
If you have any further questions concerning knob and tube, or require assistance with eliminating knob and tube in your home, please contact us.