National Electrical Installation Standards

Standards as High as Your Own

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Monday, September 18, 2017

Question:

Re: CQD answer published Wednesday, August 23, 2017 -Two wire circuits

Good Morning, This is regarding the question for August 22,2017

Although the person who presented the question didn’t specify the type of wiring in the home, I can’t recall any wiring method that didn’t provide a means of grounding at the box other than knob and tube.

Eric Samek

A

Answer:

Hey Eric thanks for your follow up question. In addition to concealed knob and tube wiring, Armored Cable Type AC and Nonmetallic sheathed cable Type NM (cloth covered type in the 1920's) were originally manufactured without an equipment grounding conductor. Cables with equipment grounding conductors that are smaller than required by 250.122 were also manufactured after that.

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