How to Troubleshoot Your Building’s Obsolete Knob-and-Tube Wiring

What is Knob-and-Tube Wiring?

Knob-and-tube (K&T) wiring was an early standardized method of electrical wiring used in buildings from about 1880 to the 1940s. It consists of insulated copper conductors run through ceramic knobs fastened to structural framing and tubes for protection through framing members.

K&T wiring has no ground wire and relies on air circulation for cooling. It was eventually replaced by safer and more efficient electrical wiring methods, but can still be found in some older homes and buildings today.

Dangers and Downsides of Knob-and-Tube Wiring

K&T wiring poses several safety hazards and functionality issues:

Signs You May Have Knob-and-Tube Wiring

Look for these indicators if you suspect your building has obsolete K&T electrical wiring:

When to Call an Electrician

Contact a licensed electrician if you notice any of the following:

These can indicate potentially dangerous wiring conditions that should be inspected immediately.

Troubleshooting Knob-and-Tube Wiring Hazards

Here are some steps you can take to assess and address safety issues with knob-and-tube wiring:

1. Check Visible Wiring

Inspect any accessible or visible K&T wiring for deterioration and damage:

2. Test Outlets

Use a receptacle tester to check for:

3. Check Wiring to Fixtures

Remove cover plates and inspect wiring to lights, switches and outlets:

4. Have an Electrician Assess

Hire an experienced, licensed electrician to conduct a thorough inspection:

Their professional assessment can reveal if repairing the existing K&T is advisable or if full rewiring is recommended.

Upgrading from Knob-and-Tube Wiring

If the K&T wiring is deemed too deteriorated or unsafe to salvage, replacement options include:

Rewiring can be costly and require extensive work, including opening up walls. But it eliminates the risks of obsolete K&T wiring for safer and more robust electrical service.

Weighing Repair vs. Replacement

Considerations when deciding whether to repair or replace K&T wiring:

Funding and Financing Options

Since rewiring or upgrades are a major project, look into any resources available:

Maintaining Old Knob-and-Tube Wiring

If unable to rewire immediately, there are maintenance steps to reduce hazards of aging K&T wiring:

With proper maintenance and vigilance, buildings with K&T wiring can stay safe and operational while planning future upgrades. But full replacement should still be a priority for long-term safety.


While obsolete knob-and-tube wiring was once standard, it poses many fire and shock dangers and functionality issues today. Homeowners should be aware of warning signs their building has K&T and take steps to assess its condition and upgrade the electrical system. With an electrician's help, deteriorated wiring can be repaired or replaced with modern wiring for safety.