Article 394 Concealed Knob-And-Tube Wiring
- Commercial garages
- Theaters and similar locations
- Motion picture studios
- Hazardous (classified) locations
- Hollow spaces of walls, ceilings, and attics where such spaces are insulated by loose, rolled, or foamed-in-place insulating material that envelops the conductors
Exception: In buildings completed before the wiring is installed, attic and roof spaces that are not accessible by stairway or permanent ladder and have headroom at all points less than 900 mm (3 ft), the wiring shall be permitted to be installed on the edges of rafters or joists facing the attic or roof space.
- Within 150 mm (6 in.) of each side of each tap or splice, and
- At intervals not exceeding 1.4 m (41/2 ft).
Where it is impracticable to provide supports, conductors shall be permitted to be fished through hollow spaces in dry locations, provided each conductor is individually enclosed in flexible nonmetallic tubing that is in continuous lengths between supports, between boxes, or between a support and a box.