A Little Bit of Knob & Tube

Happy Friday friends!  There's something interesting peeking out from the ceiling: vintage knob and tube wiring!


We're in the midst of our systems rough-ins at Norris House, so the important inner workings of the building are beginning to take shape.  Plumbing rough-ins are complete, and the HVAC system rough-ins are getting close.  Electrical rough-in work has just begun this week.  For all three of these systems, all existing infrastructure was removed during demolition.  It would have been nice to keep something, but everything was derelict and rather Jekyll and Hyde piecemeal as it sat.  Keeping the existing plumbing, mechanical and HVAC systems was never really an option - but that doesn't mean there wasn't something interesting to find!

We really are learning so much as this process rolls full steam ahead!  This is a photo of what must have been a segment of some seriously old knob and tube wiring.  We can't say for sure if this is part of the original electrical wiring of the house, but these components definitely have some age on them.  

Knob and tube gets its name from the ceramic knobs and tubes utilized to install electrical wires.  The copper wires were pulled through ceramic tubes inserted into framing (like floor joists or wall studs), and guided along their path by ceramic knobs nailed into the wooden framing.  Some quick internet research suggests that knob and tube was utilized as early as the 1880s and on into the 1930s.  Some sources claim knob and tube was used as late as the 1950s.  

It's neat to see, because it's so different from modern wiring.  Our new system has standard plastic coated wires, while the K&T's copper wires were wrapped in asphalt-soaked fabric or rubber.  The ceramic components held the wires and their heat separate from combustible wooden framing, and the lengths of wire between ceramic components were effectively suspended in open space, which allowed for heat to dissipate.  While the modern electrical wires include a grounding wire and typically run both live wires together, knob and tube systems have no grounding and the black and white wires run separately.

As with most historical systems, installation was labor intensive.  This led to greater expense, and a loss of market share as improvements in electrical wiring allowed more efficient installations.  If you want to know more about knob and tube, check the K&T Wikipedia entry!