MESSENGER SUPPORTED WIRING

321-1. Definition. Messenger supported wiring is an exposed wiring support system using a messenger wire to support insulated conductors by any one of the following: (1) a messenger with rings and saddles for conductor support; (2) a messenger with a field-installed lashing material for conductor support; (3) factory-assembled aerial cable; (4) multiplex cables utilizing a bare conductor, factory assembled and twisted with one or more insulated conductors, such as duplex, triplex, or quadruplex type of construction. 70-210 NATIONAL ELECTRICAL CODE 321-2. Other Articles. Messenger supported wiring shall comply with this article and also with the applicable provisions of other articles in this Code, especially Articles 225 and 300. 321-3. Uses Permitted. (a) Cable Types. The following shall be permitted to be installed in messenger supported wiring under the conditions described in the article referenced for each: (1) mineral-insulated, metal-sheathed cable (Article 330); (2) metal-clad cable (Article 334); (3) multiconductor service-entrance cable (Article 338); (4) multiconductor underground feeder and branch-circuit cable (Article 339); (5) power and control tray cable (Article 340); (6) power-limited tray cable (Sections 725-51 and 725-53); (7) other factoryassembled, multiconductor control, signal, or power cables that are identified for the use. (b) In Industrial Establishments. In industrial establishments only, where conditions of maintenance and supervision assure that only competent individuals will service the installed messenger supported wiring, the following shall be permitted: (1) Any of the conductor types shown in Table 310-13 or Table 310-62. (2) MV Cable. Where exposed to weather, conductors shall be listed for use in wet locations. Where exposed to direct rays of the sun, conductors or cables shall be sunlight-resistant. (c) Hazardous (Classified) Locations. Messenger supported wiring shall be permitted to be used in hazardous (classified) locations where the contained cables are permitted for such use in Sections 501-4, 502-4, 503-3, and 504-20. 321-4. Uses Not Permitted. Messenger supported wiring shall not be used in hoistways or where subject to severe physical damage. 321-5. Ampacity. The ampacity shall be determined by Section 310-15. 321-6. Messenger Support. The messenger shall be supported at dead ends and at intermediate locations so as to eliminate tension on the conductors. The conductors shall not be permitted to come into contact with the messenger supports or any structural members, walls, or pipes. 321-7. Grounding. The messenger shall be grounded as required by Sections 250-32 and 250-33 for enclosure grounding. 321-8. Conductor Splices and Taps. Conductor splices and taps made and insulated by approved methods shall be permitted in messenger supported wiring.