How to Safely Replace Dangerous Knob and Tube Wiring

Knob and tube wiring was commonly installed in homes built before 1950. This outdated wiring can be dangerous due to insulation breakdown and overloaded circuits. Replacing knob and tube wiring with modern electrical wiring improves safety and allows for additional circuits to be added. Here’s how to safely replace knob and tube wiring in your home.

Dangers of Knob and Tube Wiring

Knob and tube wiring consists of two single insulated wires running through the framing of the home. One carries the electric current while the other acts as the neutral return. The hot and neutral wires are separated by about 4 inches and supported by ceramic knobs.

This old wiring is dangerous for several reasons:

• No ground wire. Knob and tube lacks a ground wire which is essential for safety. Appliances and lights need a ground connection to prevent shocks.

• Insulation breakdown. The insulation on knob and tube wires becomes brittle and cracks over time, exposing the hot wire. This can cause shorts, fires, and shocks.

• Overloaded circuits. Knob and tube circuits are usually only 15 or 20 amps. Modern homes need 20 amp circuits for lighting and 15 amp for outlets. Overloaded knob and tube circuits can overheat.

• Difficult to repair and modify. The wires are not easily accessible, making it hard to add new circuits or replace damaged wiring.

For these reasons, knob and tube wiring poses a serious fire and electrocution risk. Replacement should be a top priority for homes that still have it.

When to Replace Knob and Tube Wiring

Here are some signs that indicate your old knob and tube wiring should be replaced:

• You need additional circuits added for a kitchen or bathroom remodel, hot tub, or other major appliances. Knob and tube was not designed to support the electric needs of modern homes.

• You experience frequent tripped breakers or blown fuses from overloaded circuits. This stresses the old wiring and insulation.

• There are visible cracks or exposed wires in the knob and tube wiring, usually seen in the attic or basement. This wiring is no longer safe.

• The wiring is covered with insulation. Insulation traps heat and moisture accelerating insulation breakdown.

• You notice outlets or devices that are warm or hot to the touch. This indicates an overloaded circuit or short and the start of a potential fire hazard.

Preparing for a Knob and Tube Replacement Project

Replacing knob and tube wiring is a major project that requires extensive planning and preparation:

• Hire a licensed electrician experienced with knob and tube replacement. This complex project is not DIY friendly.

• Get all necessary permits from your town’s building department before starting any work.

• Inspect the attic and basement to see where wiring runs. This helps plan the most efficient replacement routing.

• Take photos of all wiring before removal to reference during replacement.

• Turn off power and disconnect appliances from old circuits before beginning removal.

• Plan a staged circuit by circuit replacement to minimize work without power.

• For budgeting, expect to pay around $8-$12 per square foot depending on the home’s size and accessibility.

Proper planning makes the replacement process smoother and identifies any special challenges specific to your home.

How to Replace Knob and Tube Wiring

The basic process for replacing old knob and tube wiring involves:

Removal

• Disconnect each circuit and carefully remove knob and tube wires from the basement, attic, and walls.

• Take caution not to damage lath and plaster walls or framing when removing old wires.

• Dispose of old wiring according to your local regulations.

Installation

• Run new NM (non-metallic) sheathed wiring through walls and ceilings back to the main electrical panel. Follow the most efficient routes.

• Use 12 or 14 gauge wire for 15 and 20 amp branch circuits respectively.

• Include a separate ground wire in all new electrical runs.

• Anchor the new wiring to framing using insulated wire staples spaced per code requirements. Don’t let wiring make direct contact with framing.

• Connect circuits to new breakers in the main panel rated for the correct amperage.

• Label all circuits clearly. Reference existing circuits during replacement.

• Install junction boxes to divide long electrical runs where needed.

Safety Checks

• Verify proper grounding and polarity of all wiring.

• Perform continuity tests to check for any opens or shorts.

• Check for secure connections and anchor points.

• Insulate any exposed sections of old decommissioned wiring before enclosing walls.

Do not conceal any work until the necessary rough-in inspections by your local building department have passed.

Considerations for Partial Knob and Tube Replacement

In some cases, full knob and tube replacement may not be feasible due to budget constraints. Partial or staged replacement is an option.

Prioritize the most dangerous wiring first

• Replace any cracked, damaged, or exposed wiring. This poses the greatest fire and shock risks.

• Focus on overloaded circuits that service larger appliances like stoves, AC units, and hot tubs.

• Rewire any kitchen or bathroom circuits since these rooms involve the most electrical usage and water exposure.

Use warning labels

• Mark all decommissioned old wiring as “no longer in service” so it's not accidentally reused.

• Label any remaining live knob and tube circuits with warning flags.

Check circuits frequently

• Periodically check accessible knob and tube for further insulation breakdown.

• Monitor circuits for any new signs of overloading.

• Continue to save up for complete knob and tube replacement down the road.

With careful prioritization and vigilance, partial knob and tube replacement can provide some improved safety. But keep working towards full removal and replacement for best protection.

Ensuring Electrical Safety After Replacement

Once your old knob and tube wiring has been entirely replaced with modern wiring, there are still important safety steps:

• Have all electrical work inspected by the building department to ensure compliance with local codes.

• Perform annual thermal scans to check for hot spots that could indicate loose connections.

• Avoid overloading circuits - distribute high draw appliances over multiple circuits.

• Label all circuits clearly and update any panel documentation.

• Consider installing AFCI circuit breakers which provide additional arc fault and short circuit protection.

• Never attempt any electrical work yourself unless you are fully trained and licensed.

Replacing hazardous knob and tube wiring provides huge safety benefits and peace of mind. Maintain that safety by using your upgraded electrical system properly and scheduling any needed repairs immediately.