Knob and tube wiring replacement mostly concerns the oldest homes in Middle Tennessee towns. If you own or are buying a house with original wiring, or an inspector mentioned old wiring replacement, here's what the job involves and what to ask.
Why this old system causes problems now
Knob and tube has no ground conductor, so it can't safely support three-prong outlets without additional work. Its rubber and cloth insulation turns brittle with age. And because it was designed to shed heat into open air, it can overheat when later owners bury it under blown-in attic insulation, which happens often.
The other issue is what's been done to it. Decades of changes often mean newer cable spliced onto knob and tube, sometimes without junction boxes, and sometimes protected by fuses or breakers larger than the old wire can carry. Replacement means running new grounded cable to each device and disconnecting the old runs, often as part of whole-house rewiring.
Times it makes sense to replace outdated wiring
- You're buying an older house and the insurer or lender is asking about the wiring.
- You plan to add attic insulation over areas with knob and tube.
- A remodel opens walls in rooms still served by the old wiring.
- The home is getting a fuse box replacement or new panel.
- You want grounded outlets for computers, appliances and surge protection.
How to tell you have it (and that it's struggling)
- White ceramic knobs or tubes visible on joists in the attic or basement.
- Two separate wires running a few inches apart instead of one sheathed cable.
- Mostly two-prong outlets and very few outlets per room.
- Crumbling insulation on wires near light fixtures.
- Fuses or breakers that trip often in the older parts of the house.
Getting from old wiring to new
An electrician first traces where knob and tube is still active, since many homes have a mix. Live runs are tested and mapped. The replacement plan usually runs new circuits from the panel through the attic and crawlspace, dropping into walls to reach each outlet and switch. Old conductors are disconnected so they can't be reenergized by accident. Plaster walls slow down fishing wire, so the electrician should explain where openings are needed before work starts.
- Which circuits are still live on knob and tube
- Condition of insulation near fixtures and in the attic
- Splices between old and new wiring, and whether they're in boxes
- Fuse or breaker size on each old circuit
- Whether attic insulation is covering active wiring
Safety first. Don't add insulation over knob and tube until it's been evaluated or replaced, and don't handle it in the attic, since brittle insulation can crack at a touch. Avoid putting heavy loads like space heaters or window AC units on old circuits. If you see scorching near a fixture, stop using that circuit and have it checked.
How it usually works
Call and mention the house age
Call to connect with a local electrician familiar with older homes, and describe what you've seen in the attic or basement.
Trace and test
The electrician identifies active knob and tube circuits and checks their condition.
Plan the replacement
You get a plan covering new circuits, access points and what to expect for patching.
Replace and inspect
New wiring is installed, the old circuits are disconnected, and the work is inspected.
In Murfreesboro and Middle Tennessee homes
In Middle Tennessee, knob and tube turns up mostly in the oldest houses: some near Murfreesboro's historic courthouse square, older farmhouses in rural Rutherford County, and older homes in places like Old Hickory and downtown Franklin. Hot, humid summers make attic wiring a real concern, since attic temperatures climb high and anything that adds heat to old insulation shortens its life. If you're shopping for an older home, an electrical inspection before closing can tell you how much original wiring remains.
Related electrical problems
Seeing one of these at home? Each guide explains likely causes and what's safe to check before you call about knob and tube wiring replacement.