Differences between residential and commercial electrical wiring range from the quality, or grade, of the devices and the environments in which they work to the way the wires are run. In residential housing, conduit is generally not used at all, although its use is permitted there. In commercial electrical wiring, conduit is always used. In most cases, residential housing is single-phase power, whereas commercial wiring is mostly three-phase.
ROMEX® vs. Conduit
In residential housing, ROMEX®-style wire is used for wiring the homes. ROMEX® is a brand name of sheathed insulation conductors. As the wires in home construction are run through inaccessible areas, such as wall interiors, crawl spaces and attics, the wires are not exposed to the potential for damage. In commercial construction, wires are run in open exposed areas but protected by conduit, which prevents the wires inside from being damaged.
Wire Sizes and Types
Wire sizes used in motors, lighting and outlets are the same in commercial and residential construction; the type of wire, however, varies. In commercial wiring, the wires used are generally thermoplastic, high heat-resistant nylon-coated (THHN) and are designed to be pulled into conduit. In commercial buildings, other types of wires are used in specific situations where they may be exposed to gases, liquids or volatile substances. These wires have special insulation to protect against the expected conditions.
Single-Phase vs. Three-Phase
Residential housing generally uses single-phase power from the utility company, consisting of two 120-volt legs and a neutral wire; when testing between the two 120-volt legs, a voltmeter will show 240 volts. Commercial buildings generally use three-phase power, consisting of two 120-volt legs, a 208-volt wild leg and a neutral wire. Some large motors require three-phase power. Three-phase power allows the motors to run more smoothly and efficiently.
Commercial and Heavy-Duty-Grade Devices
In some locations, such as hospitals, a higher grade of outlet is required to provide power to sensitive equipment. These devices are much more durable and are rated to work in a wider temperature range and in environments with corrosive or chemical hazards. Most of the commercial and heavy-duty grade devices are also impact-resistant, to provide a long service life in heavily used commercial applications.