Most of the wiring in a modern home consists of runs of nonmetallic sheathed cable, or NM cable (also known by the popular brand name Romex). NM cable must be supported by framing when running through walls, ceilings, and floors. The National Electrical Code (NEC) outlines specifications for securing NM cable and other electrical wiring. Most local building authorities follow the NEC recommendations, but in any case, the local rules are the ones you must follow, and they are the specific requirements you must meet to pass inspections. Securing cables prevents excessive movement that could loosen connections or lead to cable damage.
General Cable Support
Runs of NM cable must be supported at least every 54 inches. They also must be secured within 12 inches of an electrical box that includes a cable clamp or within eight inches of a box or enclosure without a cable clamp. Keep in mind that "support" does not always mean fastening the cable to framing. For example, with a typical cable installation inside a framed wall, the cable passes through holes drilled into the wall studs for most of its horizontal run. When the cable approaches an electrical box, it makes a turn to run up or down the side of the stud toward the box and is fastened (usually with a cable staple) to the side of the stud within eight or 12 inches of the box, as required. In this common application, most of the cable is supported by the framing but is not fastened to the framing.
Use anything from a U-shaped staple to nail-on fasteners with plastic cable clips. There are a few important rules to follow when choosing and installing staples and other cable fasteners:
- Use the proper size of fastener for the size and number of cables being secured.
- Use insulated staples and fasteners. Avoid plain metal staples, and never use standard staples or other fasteners that are not designed for electrical installations.
- Position cables flat against framing before securing them; do not fasten cables on-edge.
- Secure cables snugly but not so tightly that the cable is damaged or indented from the fastener.
- Secure only one cable under each fastener, in most cases. Sometimes it is permissible to secure two 2-conductor (plus ground) cables under a single staple, for example, but it is preferable not to double up cables. It is not permissible to secure more than one 3-conductor cable under a single staple.
- Use stacker-type fasteners to secure multiple cables to the same framing member. These allow the cables to be stacked for a neater, safer installation. The clips are either nailed or screwed to the framing, and the cables are secured by clipping them into the slots.
- Avoid sharp bends in the cable immediately after a box, a drilled hole, or a staple or clip. Cables must not be bent in a radius smaller than five times the cable diameter.
Don't Forget Setback
Setback rules apply when cables run through holes in the framing or when they run parallel to and are secured to, the sides of the framing. This includes most cable runs in finished areas of the home. The general setback rule is that cables must be at least 1 1/4 inches from the face of the framing members. In a wall, ceiling, floor, or roof framed with standard lumber (2x4, 2x6, etc.) the faces are the narrow edges that get covered with drywall or other surface material. If the setback requirement cannot be met, you must protect the cable by installing a steel plate that fastens to the face of the framing, centered over the cable location. The setback requirement also means that cables cannot be fastened side-by-side on the broadsides of 2x4 studs; there isn't enough room to provide sufficient setback for both cables. That's where stacker-type fasteners come in most handy.