Conventional Components
Using conventional line voltage components, each lighting
load is turned ON or OFF by a switch. When the switch is turned
'ON', it completes the circuit, sending power to the lights.
When the switch is turned 'OFF', it breaks the circuit and
the lights go OFF.
In conventional systems, no single switching device can control anything but the simplest of circuits.
In many cases, several switching devices will need to be combined. Combining switching devices results in complex circuitry.
Low Voltage Components
A low voltage lighting control system uses a pulse-controlled latching relay to switch the lighting load.
A switching device is connected to the input of the relay, whose output connects directly to the lamp.
When a pulse from a switching device energizes the relay, it latches, turning the light ON (or OFF).
There are several advantages with a pulse-controlled latching relay. Several
different switching devices can be simultaneously connected to it with simple wiring
and they require power only when being switched.
Because of the reduced power requirements, one transformer can supply many latching relays.
And since each relay is being switched individually, a more powerful coil can be used. This larger coil greatly extends the
life of the relay contacts by creating a faster and more positive make-and-break with the load contacts.
Douglas Latching Relays can be controlled by any switching
devices that emit a compatible low voltage pulse.
These switching devices can include:
Douglas manufactures a full line of lighting control devices.
Low Voltage Control Systems
Groups of relays powered by the same transformers are mounted in a relay panel.
Barriers within the panel allow the placement of relay groups
fed by different voltages within the same panel. You could
set up one relay panel that is fed by both a 120V and a 277/347V
lighting circuit breaker panel.
You can interconnect multiple relay panels for building-wide control.
Relay scanners are the fundamental building block that permits group control of relays in one or many panels.
Here is a diagram of a sample low voltage control system
for a 3-floor commercial building. There is a relay panel
on each floor, controlling all the floor's lights. Each
room in the building has a local switch that lets occupants
turn room lights ON or OFF as desired. Each floor has a master
switch that allows the last person leaving to turn OFF all
the lights on the floor. There is a building time clock that
that turns all the lights OFF at dark with repeated OFF sweeps
every 2 hours thereafter.
A programmable relay scanner permits the connected relays
to be assigned into groups. Assigning groups is easily accomplished
with the buttons built into the front of the scanner. Up to
five groups are possible with the scanner in its basic non-networked
configuration.
A Douglas Relay Panel equipped with a Programmable Relay Scanner and a Lonworks networking node
can be networked with other scanner-node pairs to extend the size of the relay group controlled by an input.
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Low Voltage Control Systems (continued)
The Lonworks protocol utilized by the Douglas
scanner/node network is LonMark 3.1 Certified and therefore
follows all of the standard, published open protocols for
lighting control. Thus, the network can be integrated to become
part of any external Lonworks building control
system without conflict with other vendors' products.
Networks of programmable relay scanners paired with networking
nodes that include a Douglas Network Manager Module can also
be accessed and programmed directly with a PC, using the PC's
standard Internet browser (no proprietary software needed).
Designing a Low Voltage System
Once you have determined the objectives for a project's lighting control system,
you can proceed with its design. Our recommended method is to utilize a One-Line Diagram, a Reflected Ceiling Plan
and a Relay Schedule.
The One-Line Diagram shows the interconnection between panels and the switch connections
to each panel in block diagram form.
The Reflected Ceiling Plan is a plan drawing of each room or area of the project showing the
locations of the switches and the fixtures that each switch controls.
The Relay Schedule is a list of all the relays in a panel, showing numbers, circuits and switches connected to for each relay.
After you determine the line voltage circuits (this should always be done first),
start laying out the low voltage control circuits.
Follow these basic steps:
Lay out the lighting circuits on the reflected ceiling plan, then identify which circuits are relay controlled, Enter the circuit numbers and relay numbers on the relay schedule. Determine the relays to be controlled by local switches, then indicate on the reflected ceiling plan and relay schedule. Determine the relays to be controlled by master switches. Indicate on the reflected ceiling plan and relay schedule. Indicate which relays, or groups of relays, are controlled by each time clock on the relay schedule. Indicate which relays, or groups of relays, are controlled by each photocell on the relay schedule. Indicate any special requirements for a relay on the relay schedule in ‘comments’. Complete the one-line diagram.
For assistance in designing a low-voltage lighting control
system for your project, call Douglas Lighting Controls at
604-873-2797.
The above was a very brief summary. For more details on low
voltage lighting control system design, go to:
Low Voltage Lighting Control System Design.pdf
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