Both the National Electric Code (NEC) and building codes warn against overfilling electrical outlet boxes with too many components, wires, and connectors. For this reason, selecting the right size junction box is important to prevent a box that crammed – which can lead to the wires overheating or two wires touching and short-circuiting. To prevent a shock hazard, fire risk, or loss of power, consider these 3 space requirements when sizing an electrical outlet box – volume, depth, and setback.
3 Tips for Sizing Electrical Boxes
Tip 1. Determine the required Volume
The required volume of an electrical box must provide enough room for air circulation (or free space) along with plenty of room for devices, conductors, and fittings. The requirements for Box fill calculations can be found in NEC Article 314, and applies to junction boxes, pull boxes, and device boxes. When choosing an electrical box, consider the box volume in cubic inches which is the amount of space or volume inside the box and any extensions of the box such as an extension ring or domed cover.
Nonmetallic electrical boxes made out of fiberglass or polycarbonate materials will typically have the box’s volume legibly marked by the manufacturer. The total volume is an indication of the number and size of wires and wiring devices that can be contained in the box. An electrical box must have a cubic-inch capacity to house all the fittings, wires, devices, and clamps that will be installed inside the box.
Tip 2. Choosing a box Depth
Non-metallic electrical boxes are available in various depths with the most common outlet and device boxes being 2″, 3″, 4″ all the way up to 10″ deep with a progressive increase of 2-inches. But, you can also find metal, square electrical boxes with depths of 1-1/4 to 2-1/8 inches. So how do you know how deep your electrical box should be?
The depth of your electrical box will tie back to your box fill calculations. If are installing 4″x4″ outlet boxes but need more space to meet code requirements, then choose a deeper box to prevent over-crowded and avoid violating the local building electrical codes. A deeper electrical box is also used when the installed components are too large for a standard size box.
Tip 3. Consider the amount of Setback
And finally, when considering an electrical box installation make sure you take note of how much setback will be required to ensure that access to components within the box or the flush-type cover or faceplate will be flush with the finished wall or floor after construction is done. You may have to consider plaster rings or extension rings to make sure electrical panels, receptacles, or other devices are not be recessed.
Shop now at Allied Moulded Products, a major manufacturer and distributor of electrical enclosures, electrical boxes, and all the accessories you need to meet your required box volume, depth, and setback. We specialize in non-metallic electrical boxes with a large inventory of sizes from small junction boxes to large free-standing cabinets.