Understanding Knob and Tube Wiring

Knob and tube wiring was commonly installed in homes built before 1950. This old electrical system uses ceramic knobs, tubes, and cloth-covered wiring that is run through the open spaces of walls, ceilings, and floors.

While knob and tube can still function safely if undisturbed, it does not meet modern electrical codes and can be hazardous if damaged or overloaded. Common issues include:

• Insulation breakdown - The wiring is not designed to handle modern electrical loads. This can lead to overheating and fire hazards.

• Exposed wires - Damage to knob and tube components leaves conductors exposed, increasing shock and fire risks.

• Lack of grounding - Knob and tube systems do not have an equipment grounding conductor. Ungrounded outlets increase the chance of shocks.

• Difficulty adding circuits - It is challenging to tap into knob and tube to add new lighting and outlet circuits. Attempting DIY upgrades often damages old wiring.

Evaluating Your Knob and Tube System

Before making any changes, have a licensed electrician thoroughly evaluate your home's knob and tube wiring. They will check for:

• Condition of wiring insulation - Look for cracked, damaged, or deteriorated insulation along wire runs. This can indicate imminent failure.

• Presence of spliced wiring - Repairs, modifications, and taps to the original knob and tube system are prone to failure over time.

• Proper connections - Loose wire connections increase resistance and can overheat.

• ** circuits** - Knob and tube wiring is only designed to safely support devices operating at very low wattages compared to modern electrical loads.

• Signs of overcurrent - Discoloration or melting damage on wires, outlets, and other components indicates overloaded circuits.

Developing a Retrofit Plan

If your home's knob and tube wiring is deemed unsafe by an electrician, a retrofit will be necessary. There are two main approaches:

1. Partial Retrofit

This minimizes invasiveness and cost by only replacing compromised wiring. The steps include:

• Replace damaged wire runs in high risk areas like attics and crawlspaces.

• Reroute extended wires running across joists and rafters. Avoid running parallel with new wiring.

• Upgrade outlets and lighting circuits to support modern loads. Pigtail off old circuits to add new grounded circuits.

• Install AFCIs and GFCIs to protect remaining knob and tube wiring.

2. Full Rewire

For a complete overhaul, all knob and tube is removed and replaced with modern wiring. This ensures full safety and expands capacity but is highly invasive.

• All old wiring is removed back to the main panel. New cabling and boxes are installed.

• Walls, ceilings, and floors are opened to run wire through framing cavities.

• The service panel is upgraded as needed to add breaker space and capacity.

• All devices are brought up to modern codes. GFCI and AFCI protection added.

Working Safely Around Knob and Tube

When making any modifications around old wiring, special precautions must be taken:

• De-energize circuits - Turn off power at the main panel before working. Double check wires with a non-contact tester.

• Work carefully around wiring - Avoid damaging fragile textile insulation when accessing wires.

• Do not overload circuits - Use heavy duty extension cords temporarily to power high draw appliances like air conditioners.

• Connect new wiring properly - Use junction boxes and wire nuts rated for the connection. Avoid wire splices inside walls.

• Label new wiring - Clearly indicate knob and tube versus new cabling to avoid future confusion.

Hiring an Electrician

Due to the risks of improperly handling old wiring, it is highly recommended to have knob and tube retrofit projects performed by a qualified electrician. Look for:

• Proper licensing - Verify they are fully licensed and insured to work on residential electrical systems.

• Experience with old homes - Ask about their specific experience with knob and tube wiring and retrofits.

• Credentials - Look for additional credentials like NEC (National Electrical Code) training.

• References - Ask for referrals from previous historic home rewiring projects.

• Detailed quote - Get a written quote outlining the full scope of work and costs.

Upgrading old knob and tube wiring in a historic home takes skill and diligence. With proper planning and the help of a professional electrician, you can make your home's electrical system safe for modern living.