I. General
physical damage. Where open conductors cross ceiling joists and wall studs and are exposed to physical damage, they shall be protected by one of the following methods:
(1) Guard strips not less than 25 mm (1 in.) nominal in thickness and at least as high as the insulating supports, placed on each side of and close to the wiring.
(2) A substantial running board at least 13 mm O/2 in.)
thick in back of the conductors with side
398.1 Scope. This article covers the use, installation,
and construction specifications of open wiring on
insulators.
398.2 Definition.
Open Wiring on Insulators. An exposed wiring method using cleats, knobs, tubes, and flexible tubing for the protection and support of single insulated conductors run in or on buildings.
II. Installation
398.10 Uses Permitted. Open wiring on insulators shall be permitted only for industrial or agricultural establishments on systems of 600 volts, nominal, or less, as follows:
(1) Indoors or outdoors
(2) In wet or dry locations
(3) Where subject to corrosive vapors
(4) For services
398.12 Uses Not Permitted. Open wiring on insulators shall not be installed where concealed by the building structure.
398.15 Exposed Work.
(A) Dry Locations. In dry locations, where not exposed to physical damage, conductors shall be permitted to be separately enclosed in flexible nonmetallic tubing. The tubing shall be in continuous lengths not exceeding
4.5 m (15 ft) and secured to the surface by straps at intervals not exceeding 1.4 m (4'/2 ft).
(B) Entering Spaces Subject to Dampness, Wetness, or Corrosive Vapors. Conductors entering or leaving loca- tions subject to dampness, wetness, or corrosive vapors shall have drip loops formed on them and shall then pass upward and inward from the outside of the buildings, or from the damp, wet, or corrosive location, through non-combustible, nonabsorbent insulating tubes.
FPN: See 230.52 for individual conductors entering build- ings or other structures.
(C) Exposed to Physical Damage. Conductors within 2.1 m (7 ft) from the floor shall be considered exposed to
protections. Running boards shall extend at least 25 mm (1 in.) outside the conductors, but not more than 50 mm (2 in.), and the protecting sides shall be at least 50 mm (2 in.) high and at least 25 mm (1 in.), nominal, in thickness.
Boxing made in accordance with 398.15(C)(1) or (C)(2)
and furnished with a cover kept at least 25 mm (1 in.)
away from the conductors within. Where pro-tecting
vertical conductors on side walls, the boxing shall be
closed at the top and the holes through which the
conductors pass shall be bushed. (4) Rigid metal
conduit, intermediate metal conduit, rigid nonmetallic
conduit, or electrical metallic tubing. When installed in
metal piping, the conductors shall be encased in
continuous lengths of approved flexible tubing.