Knob & Tube Wiring & Home Owner’s Insurance

In recent months, a number of our clients have discovered that they can’t obtain insurance for the house they are about to buy, because it has knob & tube wiring. No insurance-no mortgage. No mortgage-no real estate transaction. Needless to say, we have had a few concerned home buyers & realtors calling us to find out why we said the house was OK & yet the insurance company says it’s not.

A significant number of insurance companies now consider knob & tube wiring unsafe or a significantly higher risk. We disagree.

It requires two wires (normally a black one & a white one, but both can be black) to create a circuit. With modern wiring, these two wires (along with a ground wire) are bundled together in a single plastic sheathing. Older knob & tube wiring was installed so that the black wire & the white wire ran separately. It was installed in houses up until about 1950. Modern wiring runs directly through holes in the structural components (such as floor joists). Knob & tube wiring used protective ceramic tubes placed in the holes to prevent the wire from chafing against the woodwork. Modern wiring uses staples to hold the wiring against structural members.

Knob & tube wiring used more elaborate ceramic knobs to clamp the wire to the structural member. Connections between modern wires are completed within enclosed junction boxes. Knob & tube wiring had visible connections. The wires were spliced & soldered together & then wrapped with electrical tape. Ceramic knobs were used to secure the wires so that anyone inadvertently tugging on the wire would not be tugging on the electrical connection. Modern wiring is typically #14 gauge copper wire & capable of handling 15 amps. Knob & tube wiring is often #12 gauge copper wire & can handle 20 amps. Note: Even though some knob & tube wiring is capable of handling 20 amps, we suggest that it be protected by 15 amp fuses because, in all likelihood, some modern #14 gauge wire may be connected to the older #12 gauge wiring.

From the above description, it becomes pretty obvious that knob & tube wiring is not necessarily dangerous. Knob & tube wiring which was installed properly, & has not been abused, can provide many more years of service. The biggest problem with knob & tube wiring has nothing to do with the original wiring. It has everything to do with what has happened after the fact.

Bloomington certified home inspectors - Knob and Tube Wiring

Most old houses do not have as many electrical circuits as new houses. If a circuit became overtaxed & 15 amp fuses were constantly blowing, some misinformed home owners would put in 25 or 30 amp fuses to “solve” the problem. Allowing 25 or 30 amps to flow through a wire which was not intended to hold that much electricity, causes the wire to overheat. This can cause the wire & the insulation to become brittle.

Some home owners also decided to add additional outlets in the house & tie the new outlets into the old wiring. Instead of making proper connections which are soldered & appropriately protected, many home owners did their own sub-standard work. They would get out the pliers & a paring knife & whittle away at the wires until a connection was made. Instead of wrapping the connection with proper electrical tape, they used hockey tape, masking tape, scotch tape or even b&-aids. It is wiring that has been abused that is potentially dangerous.

certified home inspectors Bedford - Knob and Tube Wiring

Most homes built while Knob & tube was installed did not receive insulation. So, the home owner decided to upgrade his attic space & blow in insulation, which has buried the knob & tube wiring. This presents two hazards, first it cannot release heat if the wires become heated. Second as the home owner travels through the attic space, now filled with blow in insulation, he cannot see the wires to keep from damaging them.

Knob & tube wiring, on its own, is not inherently a problem. Some would argue that knob & tube wiring does not have a ground conductor. We would remind them that even modern wiring installed between 1950 & 1960 does not have a ground conductor.

So, that is what I can tell you about knob & tube. Is it safe? YES. As long as it was not damaged, brittle, frayed, covered in insulation, or not properly modified. Out of all the knob & tube I have inspected, I can only recall once that the wires were not covered, frayed, brittle, damaged, or improperly modified. If you have or are purchasing a home with Knob & Tube wiring, upgrade it, The chances that the wires are still in the original serviceable state as when they were first installed are slim.

I report what I see, if I see bad wiring I report it, if it is covered up or in a wall section, then I cannot see it. So, the insurance companies are assuming, the wires have been damaged, altered, or are not in a serviceable state due to their age, past experiences, & the human DIY nature.

For quality home inspection in Bloomington, Bedford and its surrounding areas contact Peace of Mind Inspections! Our home inspection services includes the exterior of the home, roof system & attic, interior, foundation, HVAC, plumbing, electrical and appliances. Click here to schedule a property inspection today.

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Peace of Mind Inspections, LLC
Jym Littrell Email Us
Bloomington Office:
3802 East 3rd St Suite # 208
Bloomington, IN 47401
(812) 964-1934

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