Switches

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Introduction

Figure 1. Upper image is of a single-pole switch controlling an arrangement of luminaires. The phase wire (P) that delivers the voltage is connected through the switch. The lower image is of a multi-switch arrangement. The first and last switches in any multi-switch layout are three-way switches, while all interior switches are four-way switches. A pair of travel wires then connects these switches in series as shown, with one of these travel wires carrying the voltage in each leg of the system.

Switches are the most common means of lighting control, typically providing the user of a space with the opportunity to turn lighting on and off at one or more locations. Toggle switches provide this function by opening and closing the wire that delivers power to the lamps or luminaires (See Figure 1). Single-pole switches provide control from a single location, while three-way and four-way switches permit control from any number of locations when properly arranged in series. When multiple switch locations are used, the first and last switches in this series are three-way switches, while all interior switches are four-way switches as show in Figure 1. The two wires that travel between switches in multiple switch layouts are referred to as travel wires. A three-way switch toggles the single incoming or outgoing phase wire between the two travel wires, so one of these two travel wires is always live (with voltage) while a four-way switch either connects the two pairs of travel wires in parallel or in a crossed arrangement, again maintaining the voltage on one of the two outgoing wires by alternating which is provided with power as a four-way switch is toggled. If the last switch in a group (which must be a 3-way switch) is connected to the live travel wire, then the lighting circuit is energized and the lights are on, otherwise, they are off. Changing any switch in this configuration will alter the on/off condition of the controlled load.

Ambient lighting is typically controlled at the entrances to a space, while localized task lighting is best controlled at or near the task. Control at locations other than the room entrance may be provided for the convenience of the occupants, such as at a podium in a classroom, conference facility, or lecture hall. In public spaces, control may be through a keyed switch, remote switch or through a time clock or remote device. Energy savings can generally be enhanced through the use of smaller control zones, such as in open office areas, where smaller groups of lighting equipment would need to be energized to accommodate a single person occupying a large space. Low voltage switches, which are another control option, open and close a low-voltage circuit that signals one or more relays to open or close the phase wire that provides power to the lighting system. Relays may be individual devices installed in branch circuits or grouped within control panelboards where switching of multiple circuits can be performed. With relays, a single switch or signal from a building automation system or automated lighting control system can operate multiple circuits. Another option is to apply individual relays to the wiring system near a space, such as in a junction box within the ceiling plenum. This is how many occupancy sensor systems operate. Digital switches can be configured to control groups of lighting equipment on a digital network. The signals from these switches are typically carried by Cat5 wires or other low voltage wiring, as is the case with DALI compatible devices (see DALI under Lighting Control System Protocols). Switching of grouped lighting equipment can be performed at a DALI relay or at individual ballasts when they are assigned to the control group operated by a switch. With digital control and addressable luminaires/ballasts, control zones that are assigned to switches can be easily reconfigured, independent of how the equipment is wired. With conventional wiring, the wiring configuration determines which luminaires are controlled by each of the switches, as shown in Figure 1, with all luminaires downstream of a switch or multiple switch arrangement being controlled by that switch or group of switches.

The layout of switches in a building or individual space can provide for both control flexibility within a space and energy savings when multiple lighting control options are provided to the user. Given the option, users may not turn on all lighting equipment within a space, instead selecting a reduced lighting level they find adequate and comfortable for the current space and task conditions. For example, a reduced level may be selected when daylight is present in a space.

Switching can provide for multiple levels of general lighting, as well as separate the different types of lighting within a space by the area or surface being illuminated. Two-lamp, three-lamp, and four-lamp luminaires can have multiple lamps within a luminaire controlled on different switches, which requires that these lamps be powered by different ballasts in a fluorescent system. When lamps in different luminaires share a ballast, this is referred to as tandem wiring, which is quite common with parabolic three-lamp troffers, where luminaires can be factory linked in pairs, with flexible conduit provided between the pairs of luminaires. With tandem wired three-lamp luminaires, the center lamps in adjacent luminaires share a ballast and are switched separately from the outer lamps. Under this arrangement, all ballasts are two-lamp ballasts and fewer ballasts are required. In private offices, a wiring and control layout that provides a bi-level capability is required by some energy codes and can be integrated into a single wall plate.

In daylit spaces, if automatic lighting control is not provided, energy savings may still be possible if luminaires within a daylit zone are switched separately from luminaires outside that zone. For example, switching rows of luminaires along a window wall can provide energy savings if the occupants elect not to operate that row due to adequate illuminance being provided by daylight.

Bi-level control has been confirmed as a means of saving energy and is being applied in a wide array of applications. One example is exterior lighting, where parking lots (and parking garages) are now being configured with occupancy sensors to lower lighting levels when spaces are unoccupied, but for safety and security reasons, these systems are not turned completely off. A similar arrangement has also been applied in interior stairwells and corridors. In some cases, bi-level output is achieved through switching, while in other cases (such as for HID systems), this control is achieved through stepped dimming ballasts due to the warm-up time required when switching these sources.

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Lead Author(s): Rick Mistrick

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