Protection of Knob-and-Tube Wiring

Where knob-and-tube conductors pass through wood cross members in plastered partitions, conductors shall be protected by noncombustible, nonabsorbent, insulating tubes extending not less than _____ beyond the wood member.

a) 2 in.
b) 3 in.
c) 4 in.
d) 6 in.

See answer and applicable Code reference

The correct answer is: b) 3 in.

Article 394 covers the use, installation, and construction specifications for concealed knob-and-tube wiring. As noted in 394.17, "Conductors shall comply with 398.17 where passing through holes in structural members. Where passing through wood cross members in plastered partitions, conductors shall be protected by noncombustible, nonabsorbent, insulating tubes extending not less than 3 in. beyond the wood member."