Is knob and tube wiring illegal?
Tuesday, March 12, 2019
Existing knob and tube wiring is not illegal and not required to be removed by the building codes. But because of the safety issues with a wiring type that is obsolete, ungrounded, and all original installations are at least 70 years old, insurance companies will not write a new policy for a home with K&T still in place. That’s the big problem with buying a house with knob and tube, since nowadays you must submit a four-point inspection report to apply for insurance for an older home and the obsolete wiring will be noted in the report.
The National Electrical Code (NEC) devotes Article 394 - Concealed Knob-And-Tube Wiring to this wiring type. Here are the key limitations:
- Can only be used for extensions of existing installations. No new construction, except by special permission from the AHJ (local building department)—which is extremely unlikely.
- Not for commercial or hazardous locations.
- Cannot be used in hollow spaces with loose, rolled, or foamed-in-place insulation. Must have clearance air around it.
- Where the required clearance around the wires cannot be maintained, the individual wires must be enclosed in flexible non-metallic tubing.
The Florida Building Code—Existing Building, 6th Edition (2017) does not directly address knob and tube wiring, but states at 607.1 that “existing electrical wiring and equipment undergoing repair shall be allowed to be repaired or replaced with like material."
The most common defect we find when knob-and-tube is still in place in an older home is that it is buried under insulation, like in the photo below.
To learn more, see our blog post What is "knob and tube" wiring?
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