How to Safely Work on Your Home’s Knob-and-Tube Wiring

What is Knob-and-Tube Wiring?

Knob-and-tube wiring was an early standardized method of electrical wiring used in buildings in the United States from about 1880 to the 1940s. It consists of insulated copper conductors passing through knobs and tubes which act as insulators and physical supports.

The knobs are round or hexagonal porcelain insulators that separate the wires from each other and the surrounding surfaces. The tubes are circular or rectangular porcelain or fiber tubes that protect wires where they pass through framing members.

This old system has largely been replaced by modern sheathed cables passing through drilled holes in framing. However, many older homes still have original knob-and-tube wiring, which can present safety issues but also has historical significance.

Dangers of Knob-and-Tube Wiring

While knob-and-tube wiring was sufficient for the electrical needs of most homes in the early 20th century, it can be dangerous by modern standards. Some key risks include:

• Fire hazard - The insulation on old wiring often deteriorates over time, exposing copper conductors. This can allow wires to arc or spark and ignite nearby combustible materials.

• Shock hazard - Deteriorated insulation also creates opportunities for shocks due to exposed conductors. Grounded metal components make this worse.

• Overloading - Knob-and-tube circuits are often insufficiently rated for the higher wattage of modern appliances. Overheated wires can ignite fires.

• Unsafe splices - Splicing in additional wiring without overcurrent protection creates fire and shock risks.

• Lack of grounding - Ungrounded metal components allow shocks if a hot wire contacts them.

Evaluating Your Knob-and-Tube Wiring

If your older home has knob-and-tube wiring, it's important to have it thoroughly evaluated by a qualified electrician before undertaking any work. They should check:

• Wiring condition - Brittle, cracked, or damaged insulation increases fire and shock risks.
• Splices - These should be avoided, but if necessary, should be done safely and properly.
• Load capacity - Circuits shouldn't be overloaded beyond original design specs.
• Grounding - Grounded outlets should be added where lacking.

The electrician can then advise if replacement, upgrades, or other changes are recommended for safety. They can also identify any wiring that should be preserved for historical accuracy.

Working Safely With Knob-and-Tube Wiring

If your home still has live knob-and-tube circuits that are in good condition, it is possible to work with them safely by following precautions:

• Never overload circuits - Use appropriately rated lighting, appliances and devices to avoid overheating wires.

• Don't make unauthorized splices - Any necessary splices should be done to code by an electrician.

• Use GFCIs - Install GFCI outlets or breakers to protect against shocks in locations near water sources.

• Label live wires - Mark accessible live wires as "live" so they aren't touched inadvertently.

• Exercise extreme caution - Treat all accessible knob-and-tube wiring as potentially live. Avoid contact.

• Insulate where possible - It's usually safe to insulate attic areas around knob-and-tube runs to avoid sparks igniting insulation material.

Replacing Knob-and-Tube Wiring

In many cases, completely replacing knob-and-tube wiring provides the only way to bring an electrical system fully up to modern safety standards. Typical steps include:

• Electrical contractor performs evaluation and outlines plan and approach.

• Contractor deactivates and removes old knob-and-tube circuits.

• New grounded wiring with appropriate capacity is installed, often by fishing modern cables through walls and ceilings.

• Electrical panel may need upgrading to support added circuits.

• Fixtures, outlets, and switches are connected to the new wiring and verified functional.

• Local permits and inspections are obtained as required throughout the process.

• Historic knob-and-tube that is still in good condition can be left inactive in place if necessary.

Replacement provides maximum safety but comes at a higher cost. Grants may be available in some areas to assist homeowners with knob-and-tube replacement expenses.

Working Safely Around Deactivated Knob-and-Tube

If old knob-and-tube wiring has been made fully deactivated and dead, it can be worked around safely using simple precautions:

• Positively verify deactivated state - Have an electrician confirm knob-and-tube circuits are dead using testing equipment.

• Disable at panel - Ensure labeled breakers/fuses for knob-and-tube circuits are removed or prevented from being reactivated.

• Post warnings - Place signs and labels marking deactivated wiring as dangerous if reenergized.

• Follow good wiring practices - When running any new wiring, avoid contact or crossing of old conductors to prevent accidental energization.

• Visually inspect - Look for any signs of deterioration, improper splicing, or other issues needing remediation by an electrician.

• Exercise caution - Always work carefully around old wiring since its status can be uncertain.

Preserving Historical Knob-and-Tube

If your home has original knob-and-tube wiring that is in good intact condition, it may have historical value worth preserving. This can be facilitated by:

• Leaving significant runs of knob-and-tube in place while making upgrades elsewhere.

• Deactivating faulty wiring while retaining good condition historically important circuits.

• Labeling and documenting wiring locations for future reference.

• Taking care to avoid damage during other work.

• Working with providers experienced in evaluating and preserving period wiring.

• Checking on any available programs promoting knob-and-tube preservation through grants or waivers.

• Educating yourself on knob-and-tube to better understand what you have.

With proper care and precautions, the knob-and-tube wiring in your older home can be either adapted for continued safe use or turned into a unique historical feature to maintain. By partnering with experienced electrical professionals, you can ensure your family's safety while also preserving a bit of the past.