Hello, This is a short summary of the data we have collected working with the wiring style knob-and- tube from U.S. Electric Contractors
HOW TO IDENTIFY?:
Knob and Tube electrical wiring is installed in many types of dwellings identified by single strands of cloth wire, connected to white ceramic knobs and ran through cavities in walls and ceilings throughout your home. If there is no way for you to verify these areas you can look inside your panel to find 'Loom' over the wiring entering the panel. Loom is a black cotton braid that covers the stranded wire entering and exiting electrical boxes/ enclosures.
Another easy way to evaluate your chances of having this wiring style is to know the age of your residence. If your home was constructed before the year 1950, the chances are high that you fall into this category. Keep Reading Below!
WHEN IS IT SAFEST?:
Knob and tube is much safer where it is not enclosed or covered in any way. Open bays in your basement or attic with no insulation covering the wiring. It also will be ok in empty cavities / bays inside your walls not filled with insulation. This would be mostly interior walls but due to the age of your home, the exterior walls may not be insulated there either. Which is actually more helpful in this scenario. This summarizes the areas we have seen to be OKAY when the wiring is not disturbed or covered. There are many variables that can still deem this wiring method as dangerous even when it is installed as just described.
For example when knob and tube wiring was installed homes were constructed to accommodate very little for electrical appliances. Todays day in age many new home owners move in and set up appliances / devices with strong draws on your electrical system. This mixed with knob and tube and an worn electrical panel can be VERY dangerous
BRITTLE RUBBER COATING:
The wires in this application are coated in a brittle rubber/cloth insulation that may begin to start cracking through time with the natural settling and expansion of the home throughout the decades. This may potentially lead to the insulation flaking off entirely, exposing the bare current carrying wire to any flammable material inside of the walls /attic / basement.
The coating does not dissipate heat well AT ALL. When covered with insulation it causes overheating, melting, fire, and complete failure.
Another very important dangerous factor to knob and tube wiring would be the fact it has NO ground conductor. Grounding is by far one of the MOST important safety factors that is NEVER compromised by ANY authority of jurisdiction present day. This factor alone truly deems knob and tube wiring as unsafe by every measure of present day building standards.
Obtaining homeowners insurance that covers knob-and-tube wiring can be very difficult and can be very expensive. Few providers may offer you a policy, while many will decline to even offer a policy due to the absence of a ground wire. If not disclosed when quoted for insurance, it is more than likely not going to be covered.
More information on knob and tube and insurance can be seen here at structure tech knob and tube video!
WHAT STEPS SHOULD I TAKE?:
If your home has this wiring style, and your looking to minimize the liability, it is advised to call a licensed electrical contractor and have them review your wiring to determine the most economical way to remove this wiring from your home to better protect your home and those who live within.
WHAT CAN I DO TO BE COST AND SAFELY EFFECTIVE?:
Some very cost effective solutions we provide outside of tearing out drywall and running all new wires are:
- Updating electrical panel to ensure when overheating does occur your new electric panel with more effecient breakers are much more likely to trip and shut off the power.
- Replacing all electric switches / outlets / devices. Place gfci protected devices in locations where electronics and circuitboards are utilized.
- Replacing wiring in attic before insulation is put down.
- Replacing wiring in exposed areas to furthest points before they enter drywall.
These are very common practices we use to reduce risk / hazards / and liability with knob and tube wiring. We have technicians that are able to remove this wiring you can see more about on our electrical services page!
For more information on Knob and Tube wiring see the information provided by wikipedia!