How to Know if Your House Has Knob & Tube

Electricity is sometimes taken for granted by homeowners; however, some older homes contain wiring that should be replaced.

Indicators

Stay a safe distance from wires while performing the inspection.Stay a safe distance from wires while performing the inspection.
Knob-and-tube is one of the oldest electrical wiring methods. Age deterioration combined with the lack of grounds and circuit interruption devices can make it a fire hazard. Knob-and-tube wiring present in your home does not mean that it is live, so call a licensed electrician to be sure. If you see lengths of wiring coated in a rubbery sheath in addition to knob-and-tube, chances are you home has already been partially or fully rewired.

Step 1

Note the age of your home. If it was built after 1950, it is less likely to have knob-and-tube.

Step 2

Check the household for push-button style light switches instead of modern toggle, dial or sliding bar styles. Surface-mounted, porcelain light fixtures with exposed light bulbs and pull chains instead of wall switches are another indicator.

Step 3

Determine whether any outlets have two prongs instead of three. Modern electrical outlets include openings for at least three prongs, sometimes more, one of which is a ground. Two-prong outlets have no ground and were used with knob-and-tube wiring.

Step 4

Locate the load center, which is a fuse box in some homes and a breaker box in others. Load centers are usually large, rectangular metal boxes that are recessed in a wall. If your load center is a fuse box, knob-and-tube wiring may be present. Do not disassemble or remove the fuses and covering inside the box.

Confirmation

Step 1

Put on a pair of electrician’s insulating gloves, which will help protect you from accidental shocks.

Step 2

Access the attic or basement, or open a panel in the ceiling. Many older homes have access panels in closet walls or ceilings. Some are small, hinged doors and others are panels that pop out when you push on them.

Step 3

Shine a flashlight along the ceiling or floor joists.

Step 4

Look for thick, fabric-covered wires and ceramic knobs or tubes that are mounted to the joists. Knobs and tubes are most often white ceramic, and the wiring is black or a dark color. Do not touch the wiring or any parts of the knobs and tubes.

Things You Will Need

  • Electrician’s insulating gloves
  • Flashlight

Tip

  • The existence of knob-and-tube does not mean you are in imminent danger. An electrician will explain the process of rewiring, and he is trained to ensure the job is done properly and safely.

Warnings

  • Burn marks inside the load center, bare wires and scorch marks on the joists in the attic or basement are reasons to call an electrician immediately.
  • If your knob-and-tube wiring is surrounded with loose or batt insulation, call an electrician right away. If the wiring is live, insulation can create a fire hazard.
  • Do not touch any wiring, whether it is knob-and-tube or sheathed with a rubber coating.
  • If you cannot access an attic or basement, do not cut through the ceiling, as you could accidentally cut through live wiring. Let a licensed electrician perform the investigative work.

About the Author

Lee Carroll, a writer based in east Tennessee, has authored numerous law and DIY home improvement articles and essays. In addition to holding a degree in paralegal studies, she has more than 10 years of experience renovating newer homes and restoring historic property.