Understanding General Requirements of the NEC, Part 8

Article 110 provides general requirements for all installations. Section 110.13 provides the requirements for the mounting and cooling of equipment.

Mounting options abound, with all sorts of reliable, approved hardware available. That’s what you should use instead of flimsy means such as wooden plugs driven into holes in masonry [Sec. 110.13]. Don’t use adhesives such as construction glue (it makes equipment removal extremely difficult), caulking (it’s not suited to the purpose), or other methods of attachment /mounting not identified for the mounting of electrical equipment [Sec. 110.13].

A popular mounting means is slotted channel steel (also called strut channel) used in combination with channel bolts and devices made specifically for strut channels. This is often mounted with grade 5 stainless bolts that assemble to special locking nuts. The nuts have a special cam shape that lockisk them into place in the channel steel, so you don’t need to use lockwashers or back-wrench the connection when making it. A single ratchet is the only tool you need. Strut channel typically comes in 10 ft lengths just as metallic raceway does, and like metallic raceway it can be cut to the length you need. The versatility of this system combines with its reliability and professional appearance to make it ubiquitous in electrical installations.

Slotted channel steel is so strong and so easy to use that people use it for non-electrical purposes as well. For example, an electrical engineer built a climbing wall in his backyard on an adjustable gimbal made completely from 12 gage steel channel (the wall itself was built with 14 gage steel channel and outdoor plywood painted Navy blue to complement the industrial steel look of the gimbal). It has survived high winds, driving rain, sleet, snow, and hail for over five years.

Avoid impeding natural air flow around equipment that needs that air flow for cooling [Sec. 110.3(B)]. Dry-type transformers don’t have oil that can be cooled, so they rely on natural air flow. How you orient the transformer when setting it can make a big difference. Face the vent toward the wall, and you dramatically reduce cooling. Mount the transformer and any other equipment around it with the need for good airflow in mind.

Motors also need good air flow. Generally, the motor will have to be positioned in relation to its driven load and you have no say in what position it’s mounted. What you can do is mount other equipment so it doesn’t impede air flow to the motor, and avoid doing things such as pointing a dry type transformer vent at the motor.

In some cases, there simply will not be enough natural air flow to the motor or it is located too close to a heat source. In these cases, you can add a shroud to block hot air and a ducting system to allow the flow of cooler air to the motor. If the duct is designed properly, it will create air flow by natural induction (if the exhaust side is elevated, the warm air will rise and pull cooler air in behind it). This particular aspect is not addressed by Sec. 110.13, but the goal is the same