How to Safely Install Old Knob and Tube Wiring

Introduction

Knob and tube wiring was commonly used in homes built before the 1940s. This old electrical system utilizes porcelain knobs and tubes to run wiring through open walls and ceilings. While knob and tube can still be safe if properly maintained, it does pose risks due to lack of grounding and insulation. If your home contains knob and tube wiring, you may wish to update your electrical system. However, in some cases, you may need to install additional knob and tube wiring. This article will discuss how to safely install knob and tube wiring in an old home.

Dangers of Knob and Tube Wiring

Before installing new knob and tube wiring, it's important to understand the potential dangers:

• No grounding - Knob and tube systems have no ground wire, increasing the risk of shock. Grounded wiring helps divert current in the event of a short circuit.

• Fire hazard - The old rubber/cloth insulation can become brittle and deteriorate over time. This leaves the wiring exposed, which can lead to dangerous shorts and arcing.

• Overloading - Knob and tube is not designed to handle high wattage loads from modern appliances. Overloaded circuits can overheat, melt insulation, and cause fires.

• Difficult to replace - Knob and tube wiring is often spliced into modern wiring haphazardly. Replacing it completely can be challenging and costly.

While I don't recommend installing knob and tube wiring in new construction, you can safely build onto an existing system by taking the right precautions.

When Is It Acceptable to Install New Knob and Tube Wiring?

There are a few cases when it may be acceptable to install new knob and tube wiring:

• You're repairing or extending wiring in a historic home where preserving original materials is important.

• Code in your area still permits knob and tube. However, many jurisdictions now prohibit it.

• Budget is very limited and rewiring the whole home is not feasible. New knob and tube circuits can be a temporary, low-cost fix.

• The wiring will only supply lighting or other low-power devices. Higher wattage appliances introduce more risk.

Always check your local electrical code before proceeding. Use new knob and tube only as a last resort when rewiring is impractical. Favor safer wiring methods whenever possible.

Safety Precautions When Installing Knob and Tube

If you decide to install new knob and tube wiring, take these important safety precautions:

Use Appropriate Materials

• Wire - Use only new, UL-approved wiring. Do not reuse old cloth-insulated wiring.

• Insulators - Porcelain knobs and tubes should be in good condition with no cracks or defects.

• Junction boxes - Use UL-approved junction boxes designed for knob and tube. Do not use modern plastic boxes.

• Connectors - Use the proper vintage connectors like porcelain wire nuts instead of modern plastic connectors.

Limit Fire Hazards

• Keep wiring away from insulation, which can overheat knob and tube.

• Do not overload circuits. Use only for lighting and other low-power devices.

• Include proper overcurrent protection like fuses or breakers.

Increase Safety

• Install a GFCI receptacle at the start of each new knob and tube circuit to help prevent shocks.

• Post warning signs to identify knob and tube wiring for future homeowners and electricians.

• Only splice in UL-approved junction boxes with covers.

• Label all circuits at the junction boxes and electrical panel.

By following these guidelines, you can install new knob and tube wiring as safely as possible. However, upgrading to modern wiring should still be a priority when feasible.

Step-by-Step Installation Guide

If you decide to install new knob and tube wiring, follow these steps carefully:

1. Plan the Wiring Layout

• Evaluate where new wiring connections are needed.

• Plan the wiring route through walls, ceilings, and crawl spaces.

• Select appropriate wire gauge and overcurrent protection. Follow code requirements.

2. Install Insulators

• Secure porcelain knobs where wiring will make 90° turns.

• Install porcelain tubes between knobs where wiring will run straight.

• Allow proper clearance between wires and any wood, insulation, etc.

3. Run and Connect Wires

• Use UL-approved wiring and proper connectors.

• Make sure wiring polarity is correct.

• Feed wires into junction boxes, leave 6 inches of slack, and secure cables.

4. Attach Devices and Covers

• Install devices like lights and switches.

• Verify grounding if GFCI receptacles are used.

• Attach covers to all junction boxes.

5. Test and Troubleshoot Wiring

• Check for continuity and correct polarity.

• Verify proper device operation.

• Fix any identified issues.

By taking the proper time to plan and install the wiring methodically, you can help reduce risks when adding knob and tube circuits.

When to Call an Electrician

While a skilled DIYer can install knob and tube safely in many cases, it's best to call a professional electrician for:

• Large, complex projects.

• Working in tight spaces like crawl spaces.

• Integrating new and old wiring systems.

• Fixing problems with existing knob and tube wiring.

• Meeting code requirements for your area.

Consult with a licensed electrician before tackling projects beyond your skill level. Most electricians can also provide quotes for rewiring if upgrading the electrical system is feasible.

Conclusion

• Knob and tube wiring can still be safe if properly installed and maintained. However, it does not meet today's electrical standards.

• Only use new knob and tube wiring as a last resort when rewiring is impractical. Favor modern wiring whenever possible.

• Take safety precautions like avoiding overloads, using vintage materials, and adding GFCI protection.

• Hire an electrician if you are uncomfortable with the scope or complexity of the work.

• Rewiring with modern electrical wiring should be a long-term goal for homes with knob and tube.

While knob and tube has its limitations, following these guidelines will allow you to safely install and integrate new knob and tube circuits as a temporary fix when upgrading the full electrical system is not yet feasible.