Knob & tube wiring is a type of wiring which was in common use until the 1940′s and sometimes used as late as the 1950′s.  The nick-name is derived from the ceramic knobs that are employed to insulate and secure the wiring runs and the ceramic tubes employed to protect the wires where they pass thru potentially abrasive materials (primarily wood joists, studs etc.)  Unlike subsequent wiring systems where all the wires in a run are enclosed in a cable, the two wires (black/hot and white/neutral) run separately and only come together at a terminal (switch, receptacle, fixture, junction box etc.).

Knob & tube wiring does not provide a third wire for grounding and is therefore considered unsafe in kitchens, bathrooms, laundry rooms and outdoors.  In other areas, knob & tube wiring that is in good condition with sheathing intact, properly protected from damage, and that hasn’t been subjected to extended periods of overloading which can cause it to become brittle, should not pose an increased safety risk.

Aside from the preceding concerns, the primary risk with knob & tube wiring, it seems, is it’s relative accessibility for amateur repairs, upgrades and maintenance.   It is not uncommon to see a system with knob & tube wiring that has a history of amateur work (poorly joined connections, unfastened runs, unprotected wires, etc.).   If a house does have knob & tube wiring wiring it should be inspected to ensure that it is properly installed and in good condition. 

Note:  Many older homes with originally installed knob & tube wiring have had some of the wiring upgraded.  While modern wiring is visible in many areas, much of the knob & tube wiring may still be in place and concealed beneath floors, above ceilings and hehind walls.

If a few, but not all, of the circuits are in poor condition they can be replaced eventually without rewiring the whole house.  However, if most or all of the circuits are in poor condition, it may be more economical to completely rewire the home.   Rewiring can also allow the electrical system to be more convenient as the new circuits can be designed to accomodate the present lifestyle of the occupants of the home.

SIGNS YOU MIGHT HAVE KNOB AND TUBE WIRING: 

  • Non-Grounded Outlets:  These ungrounded electrical plugs or outlets do not have the slot for the ground prong on the end of your appliance cords.  Just changing out the electrical plugs or electrical outlets will not make the plugs grounded.  When knob and tube wiring is present in the electrical circuit, there is no ground wire for the ground on the plug to attach to.  This makes knob and tube wiring appear to be grounded when it is in fact not grounded through out the house.  Knob and tube wiring does not have a ground wire in the electrical circuit.  
  • Push Button Switches:  Push button switches were commonly installed on knob and tube wiring installations.  The push button switches may have been updated to standard switches, but if the knob and tube wiring is the original, the knob and tube wiring should be replaced by a licensed electrician working for an electrical contractor.  
  • Fuse Box:  If you still have an old fuse box instead of a circuit breaker panel, you probably still have knob and tube wiring in your home.  Our professional electricians can update your fuse box to a circuit breaker panel.  
KNOB AND TUBE WIRING and HOMEOWNERS INSURANCE
 
Before you purchase a home with knob and tube wiring, it is wise to check with your homeowners insurance to see if they will insure a home with knob and tube wiring.  Your insurance company might not insure homes with knob and tube wiring.  If the insurance company declines coverage to a home with knob and tube wiring, that should be a good indicator that the insurance company has done research on knob and tube wiring and have determined it poses a substantial risk.