CONCEALED KNOB-AND-TUBE WIRING

324-1. Definition. Concealed knob-and-tube wiring is a wiring method using knobs, tubes, and flexible nonmetallic tubing for the protection and support of single insulated conductors concealed in hollow spaces of walls and ceilings of buildings. 324-2. Other Articles. Concealed knob-and-tube wiring shall comply with this article and also with the applicable provisions of other articles in this Code, especially Article 300. 324-3. Uses Permitted. Concealed knob-and-tube wiring shall be permitted to be used only for extensions of existing installations and elsewhere only by special permission under the following conditions: (1) In the hollow spaces of walls and ceilings. (2) In unfinished attic and roof spaces as provided in Section 324-11. 324-4. Uses Not Permitted. Concealed knob-and-tube wiring shall not be used in commercial garages, theaters and similar locations, motion picture studios, hazardous (classified) locations, or in the 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. 324-5. Conductors. (a) Type. Conductors shall be of a type specified by Article 310. (b) Ampacity. The ampacity shall be determined by Section 310-15. 324-6. Conductor Supports. Conductors shall be rigidly supported on noncombustible, nonabsorbent insulating materials and shall not contact any other objects. Supports shall be installed as follows: (1) within 6 inches (152 mm) of each side of each tap or splice, and (2) at intervals not exceeding 4½ feet (1.37 m). Exception: If it is not practicable to provide supports in dry locations, it shall be permissible to fish conductors through hollow spaces if each conductor is individually enclosed in flexible nonmetallic tubing. The tubing shall be in continuous lengths between supports, between boxes, or between a support and a box. 324-7. Tie Wires. Where solid knobs are used, conductors shall be securely tied thereto by tie wires having insulation equivalent to that of the conductor. 324-8. Conductor Clearances. A clearance of not less than 3 inches (76 mm) shall be maintained between conductors and of not less than 1 inch (25.4 mm) between the conductor and the surface over which it passes. Exception: Where space is too limited to provide the above minimum clearances, such as at meters, panelboards, outlets, and switch points, the conductors shall be individually enclosed in flexible nonmetallic tubing, which shall be in continuous lengths between the last support or box and the terminal point. 70-212 NATIONAL ELECTRICAL CODE 324-9. Through Walls, Floors, Wood Cross Members, etc. Conductors shall comply with Section 320-11 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 inches (76 mm) beyond the wood member. 324-10. Clearance from Piping, Exposed Conductors, etc. Conductors shall comply with Section 320-12 for clearances from other exposed conductors, piping, etc. 324-11. Unfinished Attics and Roof Spaces. Conductors in unfinished attics and roof spaces shall comply with (a) or (b) below. (FPN): See Section 310-10 for temperature limitation of conductors. (a) Accessible by Stairway or Permanent Ladder. Conductors shall be installed along the side of or through bored holes in floor joists, studs, or rafters. Where run through bored holes, conductors in the joists and in studs or rafters to a height of not less than 7 feet (2.13 m) above the floor or floor joists shall be protected by substantial running boards extending not less than 1 inch (25.4 mm) on each side of the conductors. Running boards shall be securely fastened in place. Running boards and guard strips shall not be required where conductors are installed along the sides of joists, studs, or rafters. (b) Not Accessible by Stairway or Permanent Ladder. Conductors shall be installed along the sides of or through bored holes in floor joists, studs, or rafters. Exception: In buildings completed before wiring is installed and having head room at all points of less than 3 feet (914 mm). 324-12. Splices. Splices shall be soldered unless approved splicing devices are used. In-line or strain splices shall not be used. 324-13. Boxes. Outlet boxes shall comply with Article 370. 324-14. Switches. Switches shall comply with Sections 380-4 and 380-10(b).