Electrical Boxes, Enclosures and Cabinets

Box, enclosure or rack: settle the job before the size

This aisle runs from small wiring boxes to full cabinets, so decide the role first. Device and junction boxes hold outlets, switches and splices and come in square or rectangular shapes. Control enclosures house breakers, relays and drives, and usually take a removable back panel to mount the parts on. Equipment racks are measured in rack units (U), each 1.75 inches tall, so a 42U or 45U cabinet gives that many units of mounting height. Match internal dimensions, not outside size, to the parts you must fit.

Material and rating for where the box will live

Material follows the environment. Steel is strong and common, stainless steel resists corrosion and washdown, aluminum is light and does not rust, and ABS or polycarbonate are non-conductive and will not corrode. For outdoor or wet locations pick an enclosure with a gasketed door and a NEMA or IP rating that matches the exposure; a dry indoor room accepts a basic box. UL Listed or CSA certification shows the product was tested to a safety standard, and inspectors often expect it on mains wiring. Leave spare space for heat and cable bend radius.

Questions about Electrical Boxes, Enclosures and Cabinets

What does U mean on a rack cabinet?

U is a rack unit, 1.75 inches of vertical mounting space. A 42U cabinet offers 42 units of height for equipment, before you subtract room for shelves and cable management. Standard racks take equipment with a 19-inch wide front panel.

Can I use a plastic box for mains wiring?

Often yes, if the box is certified for the purpose and suits the cable and the location. Metal boxes must be bonded to earth; plastic ones need no bonding but may not suit high heat, impact or heavy fixtures. Follow your local wiring rules.

How do I choose the enclosure size?

Lay out every part you need to mount, then add room for wiring, cable bends and heat, plus spare space for later additions. Compare that layout with the interior dimensions or back-panel size, not the outer size, when comparing models.