Switches

You can turn a light on and off either by plugging a lighting fixture into an electrical outlet (receptacle) and turning the switch on the lighting fixture on and off, or by hard wiring the lighting fixture directly into the building's power supply system and using a wall switch to control the power. Switches up to 30 A that can be outlet-box mounted are considered wiring devices.

A common wall light switch is a type of general duty safety switch called a contactor. Contactors close an electrical circuit physically by moving two electrical conductors into contact with each other, allowing the power to flow to the lighting fixture. The contactor physically separates the two conductors to open the circuit, which stops the electrical flow and shuts off the light. Manual and remote pushbuttons use contactors to operate remote controls. Manual or remote pushbutton contactors can also be used with automatic devices such as timers, float switches, thermostats, and pressure switches. They are found in lighting, heating, and air-conditioning equipment, and in motors.

Contactors can be operated by hand, electric coil, spring, or motor. A wall switch is an example of a small, mechanically operated contactor. A relay is a small electrically operated contactor. The operating handles for contactors may be toggle, push, touch, rocker, rotary, or tap-plate types (Fig. 31-4). Mercury and AC quiet types of handles are relatively noiseless, while toggle, tumbler, and AC/DC types are not. A toggle switch has a lever or knob that moves through a small arc and causes the contacts to open or close the electric circuit. Keyed switches are used where access needs to be limited to authorized people. Tumbler-lock controlled switches are used where a keyed switch does not provide adequate security, as where keys may be stolen. Spring-wound timer switches are often used for bathroom heaters and ventilation fans.

General duty safety switches are intended for normal use in lighting and power circuits. Heavy-duty (HD) switches are used for high-fault currents subject to frequent interruption. They also offer ease of maintenance. Switches are installed in hot wires only. They disconnect an electrical device from the current, leaving the

Add a small programmable memory circuit—an erasable programmable read-only memory (EPROM) chip—and you have a programmable time switch. A programmable switch fits into a wall outlet box just like an ordinary switch. It uses miniature electronics for lighting, energy management, automated building control, and clock and program systems. For example, a readonly memory (ROM) chip can be programmed with the sunrise and sunset information for the latitude involved, thus becoming a "sun tracker," which can control circuits with dark-to-dawn control year round.

An even more sophisticated switch adds a microprocessor, giving it the ability to respond with a particular control plan to given input signals. This programmable controller uses programmable memory to store instructions that implement special functions. It amounts to a special type of computer that has a short program within its hardware for a specific type of function, such as logic, timing, counting, or other functions. Such switches are used in industrial controls, process controls, and elevators.

Wireless switching and control is undergoing extensive development. Wireless bandwidths are getting much bigger. The use of wireless devices will have a significant impact on building design. Wireless systems are finding a niche in facilities with fixed architecture, but in offices where the need for flexibility dictates partitions that can be quickly reconfigured, the benefits may be significantly reduced. For wireless systems to function properly, the locations of transceivers, the configuration of a space, and the number of users must all be coordinated. This can make a wireless office considerably less flexible than one with underfloor communications wiring distribution, which can be easily reconfigured.

To date, the trend toward the delivery of ever-larger amounts of information, at ever-greater speeds, directly to the desktop favors wired technologies over wireless devices. The bandwidth of today's wireless networks is narrow, which puts a limit on the amount of data that can be transmitted per second. Also, bandwidth is shared, which means that any one user's access is restricted as the number of users increases. These drawbacks, coupled with potential security problems inherent in wireless communication, make wireless systems a less desirable substitute for wire infrastructure in most office environments, except in very specific applications. However, all this may change as the technology continues to develop.

Interior designers often indicate the location of switches on their drawings. Switches to control lighting or receptacles are usually positioned on the handle side

Rocker plate switch

Conventional toggle switch

Rocker plate switch

Conventional toggle switch

Dimmer switch

Figure 3Í-4 Common types of wall switches.

Dimmer switch

Figure 3Í-4 Common types of wall switches.

device with no voltage going through it, and eliminating the possibility of shock when the switch is open.

A three-way switch is a switch used in conjunction with another switch to control lights from two locations, such as from the bottom and top of a stairway. An ordinary single-pole switch has "on" and "off" written on it. A three-way switch has three terminals, so the on and off positions may change, depending on the position of the other switch. Four-way switches are used in conjunction with two three-way switches to control lights from three locations.

Remote-control (RC) switches are used for switching of blocks of lighting or for exterior lights. They can control whole floors or whole buildings. They use electromagnets to operate fixtures from a distance without wiring. Ceiling fans and electrically operated window treatments often use remote controls.

Solid-state switches are beginning to replace the common wall switch. Solid-state switches use an electronic device with a conducting state and a nonconducting state, similar to a conventional switch in closed position and open position. The change between the two states is accomplished by a control signal in the voltage. The change is made instantaneously, noiselessly, and without sending a flash of electricity across a gap. With an electronic timing device added, you have a time-controlled electronic switch with no moving parts, acting independently of utility line frequency.

A switch with a solid-state rectifier makes it possible to switch incandescent lamps from high to low to off. They cost very little more than an ordinary switch, and can save energy where a lower illumination level is often acceptable.

of the door of a room. The interior designer's drawings should show and identify plug-in strips on walls and special purpose receptacles. Use special symbols and notes to locate signal outlets for fire alarm, telephone and intercom, data and communication, radio and TV, and other equipment. The circuits for these types of equipment are not usually indicated on the floor plan, but are instead shown on a separate power plan. Lighting fixture outlets are usually included with wiring devices, unless this leads to a cluttered drawing, in which case they are represented on their own drawing. Motors, heaters, and other fixed, permanently installed equipment is shown and identified on power plans rather than on lighting drawings. Equipment with a cord and plug is not usually represented, but receptacles for plugin equipment are shown and identified.

Lighting dimmers originated as large, expensive pieces of equipment for theater and display lighting. Today, modern wall-box dimmers are small electronic units. The simplest dimmers are rotary incandescent dimmers. Older units, and some inexpensive current units, produce annoying radio frequency interference and line harmonics that can affect computers and other electronic equipment. Newer dimmers use preset controls combining dimming and switching. They are used for smooth fan speed control, for remote and local con trols, to provide automatic fadeouts, and to dim fluorescent lamps provided with dimming ballasts.

Dimmers, switches, receptacles, fan controls, cable TV, and telephone jacks are all available in a variety of colors. Be aware that cover plates specified in a bold color may have to be replaced if the wall color or other decor is changed.

Normal full-voltage switches are wired directly into the load circuit and operate at line voltage and full current. Common ratings include 15 A, 20 A, and 30 A; and 120V or 120/277V. Low-voltage switching is used for remote control switching. It uses light-duty, low-voltage 24V switches to control line voltage relays, which then do the actual switching. Low-voltage switching allows flexibility of location for the controls. Low-voltage, low-current wiring is less expensive than full-voltage wires and conduit. The system gives flexibility and makes changes simpler. The status of individual loads can be monitored at a central control panel by use of relays with auxiliary contacts. Low-voltage switching is also used for group load override by central control devices like timers, daylighting controllers, and energy management systems, and for individual load control override by local control devices, such as occupancy sensors and photocells. These are important elements of an energy conservation system.

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