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Tips for Selecting the Right Electrical Box

Oct. 17, 2017
Determine what kinds of tubing or conduit connectors you’ll use before selecting the boxes for a run when laying out raceway.

When laying out raceway, always determine what kinds of tubing or conduit connectors you’ll use before selecting the boxes for that run. Why would you do this? Because you can’t use round boxes when those connectors require locknuts or bushings [314.2]. To work properly, they need a flat plane. Manufacturers publish tightening instructions; for example, “snug fingertight then give it a quarter twist with pliers.” The “old school” way is to (mis)use your screwdriver by placing it against the nut and giving it a solid whack.

Boxes in a metallic raceway system must be metallic and must be installed for mechanical integrity and electrical continuity with the raceway. Any time you use metal boxes, ensure they are bonded and grounded per the applicable requirements of NEC Art. 250, Parts I, IV, V, VI, VII, and X [314.4]. Note: A metallic raceway is typically part of the equipment grounding conductor (EGC).

You can use nonmetallic boxes only with nonmetallic raceway, open wiring on insulators, concealed knob-and-tube wiring, cabled wiring methods with entirely nonmetallic sheaths, and flexible cords [314.3]. However, two Exceptions follow this rule.

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