Control wiring is used to communicate commands and other information between control devices in a lighting system.
“Proper control wiring is like the nervous system in the human body,” said Ronald Bryce, national sales manager for PLC-Multipoint Inc., Everett, Wash. “The brain monitors the conditions of the organs and parts of the body, sends orders to the muscles and receives acknowledgment that those orders were received and acted upon. Just like a poor nervous system, improper control wiring creates problems for the control system.”
In a traditional lighting system, line-voltage wiring (Class 1, typically 120V or 277V AC) provides both power to lighting fixtures and also a means of grouping them by circuit/switch-leg within “control zones.” The most basic form of communicating with this zone is to provide or remove electric power using a controller, which turns the zone on/off.
Line-voltage wiring also can serve as a pathway for control signals. Power-line carrier communication has several advantages. It can serve as a reliable path for simple on/off signals and, depending on the environment, raise/lower dimming signals; can be run with other line-voltage wiring in the same conduit; enables long runs; and allows multiway applications using travelers. It is particularly economical in control retrofit situations because it will already be installed. In addition, electrical workers are very familiar with it.
However, it is not very flexible, imposing limited control options and rigid zoning based on lighting circuiting. Most codes require line-voltage wiring to be installed in protected runs, such as conduit.
For more advanced functionality and flexibility, dedicated control wiring may be needed. This wiring is low voltage (Class 2, typically 10–24V DC) and provides a pathway for communication of analog or digital signals, such as incoming sensor input data—e.g., light levels, occupancy conditions—and outgoing commands. It is inherently flexible as most codes do not require it to be installed in conduit; in such cases, plenum-rated wiring can simply be laid on top of suspended tiles. And it is safer to install.
As lighting systems increasingly become automated, knowledge about low-voltage control wiring methods becomes more important.
“Controls are becoming more popular and prevalent due to energy codes and the energy savings available using controll-able technology,” said Greg Bennorth, director of system projects for Universal Lighting Technologies, Nashville, Tenn. “Controllable systems are being designed to minimize and simplify their wiring to make systems more cost-effective and easier to install.”
In the United States, the most common types of low-voltage wiring are analog 0–10V DC and digital. Analog 0–10V wiring consists of two wires with a 1–10V potential between them. It does not have to be installed in conduit (and should not be installed in conduit with power wiring), but note that it can present a poor signal-to-noise ratio, sensitivity to polarity, and fixture-to-fixture light output variations when dimming across long runs. Wiring sizes typically vary from 22 AWG to 14 AWG, with a common size being 18 AWG. The wire is typically stranded copper as it is considered easier to work with and provides a more stable path for current.
The wiring may be shielded or unshielded. Since low-voltage wiring is sensitive to electrical noise and electromagnetic interference, shielding provides some immunity when these issues are a concern. Additionally, shielded or unshielded Category 5 and Cat 6 twisted-pair wiring offers, for a cost premium, some immunity against interference in electrically noisy environments.
Digital wiring uses two wires with a maximum potential of 18V between them. This wiring forms a single bus connecting all control devices, resulting in simpler, more elegant wiring configurations and other benefits. Digital wiring also provides the foundation of dramatically expanded capabilities, depending on the protocol and system.
“The major evolution has been and will continue to be from analog to digital,” said Pete Baselici, senior product line manager for Legrand WattStopper, Santa Clara, Calif.
Control wiring is typically transported in bulk and cut in the field to required length easily. Some manufacturers offer structured wiring options, such as factory-installed terminations with RJ-45 (computer), RJ-11 (telephone) or proprietary connectors. This can simplify installation for installers, although it involves predetermined wire lengths.
“There has been a movement to simplify wiring requirements for control systems and make it more robust,” said Thomas Hinds, product manager–fluorescent dimming ballasts for Lutron Electronics Co. Inc., Coopersburg, Pa. “Wiring has become easier to install, less prone to miswiring, and more immune to external electrical noise interference.”
“Ten years ago, control wiring was simply a switch leg providing on/off control,” said Andrew Parker, PE, LC, director of sales, Encelium Technologies, Teaneck, N.J. “Analog dimming technology brought the ability to continuously adjust light levels to ballasts grouped independent of lighting circuits. Today, digital networking technology has revolutionized lighting controls, allowing multiple energy management strategies to be deployed at the individual fixture level.”
Look for Part 2 next month.
DILOUIE, a lighting industry journalist, analyst and marketing consultant, is principal of ZING Communications. He can be reached at www.zinginc.com.