Chapter 5 Wiring Methods 65 Copyright Goodheart-Willcox Co., Inc. 5.1.2 Securing and Supporting Wiring Systems All wiring must be secured to and supported by structural members. Normally, wiring sys- tems are not used to support other wiring systems or nonelectric equipment. However, Section 300.11(B) of the Code specifi es some con- ditions under which one raceway can be sup- ported by another raceway. Mechanical and electrical continuity is required. Metal conduit, cable sheaths, cable armor, and nonmetallic raceways must be con- tinuous between boxes, enclosures, fi ttings, and cabinets. All connections between the compo- nents must be secure prior to pulling conduc- tors. The equipment grounding conductor should be independent of the device connec- tion, so if the device is removed, the continuity is not interrupted. Conductor Support in Vertical Raceways In buildings where raceways are run vertically, the conductors must be supported at assigned intervals. One cable support at the top of the raceway run and at intervals indicated in the table in Figure 5-5 are required. This table is a condensed version of Table 300.19(A) from the Code. Support of vertical conductors can be accom- plished in several ways, including the following: • Placing insulated wedges between the cable and the inside wall of the raceway or using insulated clamps within an enclosure. • Installing junction boxes with supports installed and attached to the cable. • Installing junction boxes and offsetting the cable at least 90° and using tie wires within the box. 5.1.3 Wiring within Air-Handling Spaces No wiring is permitted within air-handling ducts used for the purpose of transporting dust, fl ammable vapors, or cooking equipment ven- tilation. In plenums used for environmental air only, wiring methods employing type MI or MC cable are permitted. Flexible metal conduit and liquidtight fl exible metal conduit are also permitted in short lengths (not more than 4′) to connect sensors, louvers, and other devices per- mitted in these plenums. For other types of air-handling ducts, refer to Code Section 300.22(C) and the local inspection authority, which may have special requirements applicable to the specifi c conditions. CODE ALERT Junction Box Cable Support According to Section 300.19(C)(3), when the cable is supported by bending it at least 90° in a junction box and securing with tie wires, sup- port intervals cannot exceed 20% of the normal maximum support distance. The bend in the conductor must extend horizontally at least twice the diameter of the cable. Goodheart-Willcox Publisher Figure 5-5. Condensed version of Table 300.19(A) of the Code. Vertical Spacing for Conductor Supports Conductor Size Maximum Distance between Supports (in feet) Copper Conductors Aluminum Conductors 18 AWG through 8 AWG 100 100 6 AWG through 1/0 AWG 100 200 2/0 AWG through 4/0 AWG 80 180 Over 4/0 AWG through 350 kcmil 60 135 Over 350 kcmil through 500 kcmil 50 120