Two-pole switches can control two separate circuits at the same time. For example, a large room may need two lighting circuits. If only one switch is needed, use a single two-pole switch. Several two-pole switches can be ganged to control a number of circuits. This reduces the labor, switch, and box cost.

Many offices require two-level lighting. Regulations designed to reduce energy consumption sometimes require two-level lighting in all office buildings. Each four-lamp fluorescent fixture will have two lamps controlled from one switch and two lamps controlled by another switch located immediately beside the first. When there are more than two circuits involved, two-pole switches can be used in the same two-gang switch box.

Three-way switches allow switching a lighting circuit from two separate locations. For example, in a hall you want lighting controlled from switches at either end. On a stairway you want lights controlled from both upstairs and downstairs.

Four-way switches are used where three switches need control of the circuit. The four-way switch is connected into the switching circuits between two three-way switches.

There are two types of switches with illuminated handles. One lights when the switch is in the "ON" position. The other lights when the switch is in the "OFF" position. Either can be used as a pilot light. But be sure you order the right switch. They're not interchangeable and can't be modified on site.

The switch that lights when the switch is on is used where the switch and the fixture or appliance are in different rooms -- such as the light for a storage room or closet.

The switch that lights when the switch is off is used in rooms that are normally dark when unlighted. When the switch is on, the handle isn't illuminated.

Quiet (silent) switches are a good choice for better-quality homes and offices. You'll hear these called mercury switches, but they may or may not be made with mercury contacts. Quiet switches come in voltages to 277V.

Heavy duty "T" rated switches are made for heavy loads. The circuit is closed by a contact armature that moves very fast to minimize arcing when the switch changes position.

Decorative wiring devices are offered by some manufacturers. Unlike standard devices, decorative devices are generally rectangular. The trim plate is designed to fit only a decorative style device. And note that trim plates made by some manufacturers for decorative switches won't fit decorative duplex receptacles by the same manufacturer. That creates a problem when placing a decorative switch and a decorative duplex receptacle in the same box.

Horsepower-rated switches are used to control small motor loads, such as exhaust fans, where manual motor starters are not required. The motor has a built-in overload protector.

Key-operated switches are common in public areas where lighting shouldn't be controlled by the public -- for example, in a public restroom where the light has to be on while the building is open to the public. Key switches come with either a simple stamped 2-prong key or a conventional lockset.

Duplex switches have two switches mounted in a housing shaped like a duplex outlet. They can be wired to control two separate circuits or to control one circuit with two loads. Duplex switches can be used to control two-level lighting in an office.

Momentary-contact switches provide current only for an instant. When not being activated, the switch is always open. Momentary switches are commonly used to throw another switch like a lighting contactor that controls a large bank of fluorescent lights. If the lighting contactor has a close and open set of coils, a momentary-center-off switch is used. The contactor is closed when the momentary switch handle is lifted to the on position. When the switch handle is released, it returns to the center position. To de-energize the lighting contactor, the momentary switch is pushed down to the off position. Any time the momentary switch handle is released, it returns to the center position.

Every modern wiring device has a voltage and amperage rating. This rating has an effect on cost. Usually, the greater the ampacity and voltage rating, the higher the cost.

Devices intended to meet exacting specifications or to serve in special applications are said to be specification grade. Usually these devices are made with more expensive contact material, are designed with special features, or are built to be particularly durable. That increases the cost, often to several times the cost of the standard-grade device. But the added cost may be a good investment from the owner's standpoint. For example, one specification-grade convenience outlet has contact material with better shape-retention characteristics. That ensures better electrical contact after years of hard use. You've probably seen duplex outlets that will hardly hold an electrical plug in place after a year or two of service.

Most manufacturers offer wiring devices with smooth surfaces that stay cleaner longer -- and are easier to clean when they do get soiled. Older switch covers had decorative grooves that accumulated smudges and were hard to clean.

Standard colors for wiring devices are ivory, white and brown. Other colors are available but will cost more.