How to Fix Old Knob and Tube Wiring in Your Home

What is Knob and Tube Wiring?

Knob and tube wiring was an early standardized method of electrical wiring used in North America from about 1880 to the 1940s. It consists of single insulated copper conductors run within wall cavities, passing through joists and studs.

The conductors are supported on ceramic knobs and separated from each other by about 1 inch by ceramic tubes at crossover points. This method of wiring has largely been replaced by safer and more efficient systems, but may still be found in some older homes.

Dangers of Knob and Tube Wiring

Knob and tube wiring can pose several safety hazards:

• Fire risk - The insulation on old wiring often deteriorates over time, exposing bare copper that can arc, spark and ignite flammable materials within walls.

• Shocks and electrocution - Damaged wiring can energize metal appliance frames, pipes, and other conductive surfaces, posing a serious shock hazard.

• Insufficient capacity - Knob and tube circuits are often undersized for modern loads like air conditioners, leading to overheating.

• Lack of grounding - Most old systems have no equipment grounding conductors, increasing risk.

Signs You May Have Knob and Tube Wiring

Here are some signs that a home may still contain old knob and tube wiring:

• Two-prong ungrounded outlets
• Blown fuses or tripped breakers from overloads
• Older electrical panels with fuse boxes
• Outlets and lights stop working when large appliances turn on
• Discolored or cracked outlet and switch plates
• Exposed knobs and tubes in unfinished basements or attics

Options for Replacing Knob and Tube Wiring

If your home contains old knob and tube wiring, here are some options for replacement:

Full Rewiring

This involves removing all old wiring and installing entirely new circuits and wiring throughout the home up to modern electrical code. This ensures maximum safety and capacity but is the most expensive option. Expect costs of $8,000-$15,000.

Targeted Rewiring

With this approach, only the most problematic wiring is replaced by running new wiring in easier to access spaces like attics and basements. Keep costs lower at $2,000-$8,000 but doesn't address all risks.

Pigtailing

Individual circuits are upgraded by splicing short sections of modern wiring into existing wires. Very cost effective at $1,000-$2,000 but doesn't replace old wiring within walls.

DIY or Hire an Electrician?

Replacing knob and tube wiring is a complex project best left to licensed electricians familiar with old electrical systems. Mistakes can lead to fires or electrocution.

However, minor targeted improvements like pigtailing individual circuits may be DIY-friendly. Always get proper permits and have work inspected.

Prioritizing the Replacement Project

When planning and budgeting your wiring replacement project, focus first on:

• Circuits supplying major appliances like refrigerators or laundry, which may be overloaded.
• Wiring with damaged or degraded insulation.
• Areas with high fire risk like kitchens, attics, and garages.

Safety Tips for Homes with Knob and Tube Wiring

If full rewiring isn't possible right away, here are some tips for managing risk:

• Have an electrician install GFCIs on ungrounded circuits.
• Use bulbs with lower wattage to reduce overloads.
• Don't run high-draw appliances like air conditioners on suspect circuits.
• Don't run wiring within walls or hide knob and tube with insulation.
• Check for warmth or discoloration in outlets and wiring.

Replacing aging knob and tube wiring improves safety and prevents fire risks. Prioritize high-risk areas but consider fully rewiring over time.