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Boston Addresses Knob and Tube Wiring

The purpose of this article is to describe, with some detail, effective means to address knob and tube wiring in older Boston homes without completely removing it. Ultimately complete removal is, in fact, my recommended action whenever knob and tube is present, however its often found in low income areas where complete replacement is just not possible financially. In those situations, and only those, there is an alternative method that involves managing and monitoring the risk associated.

As far as managing the risk, the first issue that should be addressed is with additions to original wiring that may have been made. All additions to knob and tube wiring that were not made with original means (as in more knob and tube) should be removed. Second all possible actions should be taken to ensure that all exposed wiring is not subject to physical damage or exposed to flammable materials, including spider webs, insulation and dry lumber. Next a grounding electrode system should be installed at the service entrance that includes 2 electrodes and water pipe bonding where necessary. Equipment grounding conductors should be ran from any point of the grounding electrode conductor to every switch, receptacle and fixture, in the house. In the event The equipment ground can not be pulled to the fixture due to cost the fixture should be replaced with a fixture rated for use without an equipment ground. This often means removing elaborate antique fixtures with exposed metal parts. Finally, and most importantly Arc Fault breakers must be installed on every circuit.

Monitoring the risk would requiring no less then monthly visual and mechanical inspections with a megger tester, and comparing recorded results. I would not use this method unless it was coupled with a detailed course of action that included scheduled eventual replacement of all knob and tube.

While using this method you would essentially be pulling a wire to every device it would be much less out of pocket initial expense and allow a homeowner to budget accordingly. Replacing knob and tube is not a diy electrical repair project and should only be done by qualified electricians.

Likely issues you may encounter could include, flying splices where knob and tube wiring is openly spliced to a piece of NM (romex type wire) this must be removed and ran back to the panel. Bronx wire (also called bx) may be even more dangerous then the knob and tube. Often you will find the outer metal jacket used as an equipment ground and feeding circuits with grounded outlets, this is a VERY bad practice. The fact is that while the outer metal jacket of bx may read a low impedance with a typical continuity tester, under load and fault conditions, the outer jacket can get red hot because it does not effectively conduct fault currents to ground.


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