How a Forgotten Knob-and-Tube Wiring System Could Burn Down Your Home

As a homeowner, I never imagined that the hidden wiring inside my walls could be a fire hazard. That changed when I learned about an antiquated electrical system called knob-and-tube wiring. This forgotten wiring method was common in homes built before 1950 and can pose serious fire risks if left in place. In this article, I'll explain what knob-and-tube wiring is, why it's dangerous, how to detect it, and what you need to do if your home still contains this outdated wiring.

What is Knob-and-Tube Wiring?

Knob-and-tube (K&T) wiring was commonly installed in American homes built between 1880 and the 1940s. It consists of single black rubber-insulated wires passing through ceramic knobs mounted on framing and tubes used to protect wires through open spaces.

Unlike modern electrical wiring systems which use a grounded metal conduit to protect wires, K&T wiring is completely ungrounded and provides no protection from incidental contact. The wires are often covered in cloth or tar paper insulation that can easily crack or deteriorate over time.

Why Knob-and-Tube Wiring is a Fire Hazard

There are several factors that make aging K&T wiring a serious fire risk:

• No grounding - Without a ground wire, a fault in the system could energize metal components in your home. This can lead to electrical shocks or sparks that can ignite fires.

• Insulation deterioration - The original cloth or tar paper insulation often breaks down over time, exposing bare wires that can arc and spark.

• Overloaded circuits - K&T wiring was designed for smaller electrical loads. Connecting modern high-wattage appliances can overload the system and cause wires to overheat.

• Unsupported wires - K&T wires are simply hung through open spaces and can sag over time, coming into contact with combustible materials.

Any of these factors can lead to electrical fires that can spread rapidly through homes. K&T wiring caused an estimated 25,000 fires per year in the late 1980s according to the Consumer Product Safety Commission. Fires often start in walls and can go undetected for a long time.

How to Check if Your Home has Knob-and-Tube Wiring

If your home was built before 1950, there's a good chance it contains at least some K&T wiring. Here are some ways to check:

• Inspect the basement, attic, and garage for wires passing through ceramic knobs and tubes. K&T wiring is often exposed in these unfinished spaces.

• Remove a wall plate on a light switch or outlet and check if there are two separate wires with black rubber insulation rather than modern Romex cable.

• Check for notches or holes drilled in wood framing to pass K&T wires through. Modern wires are simply stapled to the sides of studs.

• An electrician can use a specialized thermographic camera to scan inside walls for hot spots that may indicate faulty knob-and-tube wiring.

If you confirm or even suspect there is old K&T wiring present, it's essential to take action to prevent a fire tragedy.

What To Do if Your Home Has Knob-and-Tube Wiring

Here are your options if you discover K&T wiring in your vintage home:

• Full rewiring - This is the only way to completely remove the fire hazard. It involves pulling all new wired through your home up to modern electrical codes. This is costly, invasive, and time consuming.

• Targeted replacement - With this approach, K&T wiring is removed from high risk areas like the kitchen, laundry, or bathrooms and replaced with modern wiring. The rest can be left in place or de-energized. This reduces but doesn't eliminate the hazard.

• Circuit breaker panel upgrade - Upgrading to a modern circuit breaker panel with GFCI outlets can add some protection, but does not address insulation degradation or overloading issues.

• Electrical load management - Avoid plugging high-wattage appliances into outlets serviced by K&T wires. But this is only a temporary solution.

The only sure way to remove the fire risk is a complete rewiring. While expensive, this will drastically improve the safety and value of your vintage home. If full rewiring isn't feasible right away, prioritize the most hazardous areas first. But never ignore old knob-and-tube wiring - it could lead to the destruction of your beloved historic home.