Throughout this tutorial you will see examples of metal boxes and plastic boxes. If you are using metal conduit to run wiring to the electrical box, then a metal box is required because the conduit and metal box system itself may be used to ground the system. If you are using non-metallic wiring Type NM-B (nonmetallic-sheathed cable) which is typically found in residential applications as branch circuits for outlets, switches, lighting and so on, then you can use either plastic boxes or metal boxes as long as the cable is secured to the box. With NM-B, grounding occurs with a dedicated wire made part of the cable.
Type NM-B electrical cable is the most common way to wire a home and you may hear it referred to generically as Romex®. However Romex® is a brand name of Southwire Co. for NM cable just as Kleenex® is often used to describe facial tissue.
Metal boxes come in types known as:
- Drawn Steel (1 piece construction);
- Interlocked / Gangable (typically for switch and outlet boxes).
- PVC (most common);
- Phenolic Resin;