EE102B: PANEL-BASED CONTROL SYSTEMS
INTRODUCTION
Turning lighting OFF when it is not being used saves energy. Automating that function is the
most reliable method. As a result, most commercial building energy codes require automatic
lighting shutoff. This common-sense strategy also adds value to lighting upgrades in existing
buildings.
To turn the lighting OFF automatically along a branch circuit, we must add a switch. This
switch features a low-voltage input to accept control signals and a line-voltage output to
control the load. Switching may be local, such as a vacancy sensor turning the lights OFF in a
room, or remote. Remote switching concentrates switches in a central assembly that may
feature intelligence, which allows programming such as scheduled ON/OFF. This assembly
resides in a metal cabinet-type enclosure called a panel.
The panel, in turn, can serve as the backbone for a complete energy code-compliant control
system that responds to a wide range of control inputs for indoor and outdoor lighting control.
It is typically sold as a new complete unit, though panelboard retrofit assemblies are available.
This learning module describes common panel-based lighting control systems.
Image courtesy of Eaton
LEARNING OBJECTIVES
By the end of this course, you will be able to:
● Apply load-scheduling strategies to commercial buildings.
● Select an appropriate load-scheduling strategy to achieve lighting automation.
● Select appropriate features for the equipment.
SWITCHGEAR
Switchgear consists of power-switching devices used for electrical protection, electrical
isolation, and local and remote switching. Electrical codes require that circuit breakers feed
and protect each circuit. For remote lighting control, the circuit adds a switch to change the
load.
The circuit breaker may integrate this switch, resulting in a controllable circuit breaker that
provides both electrical protection and remote switching. Or the system may add low-voltage
relay switches (called contactors when controlling very large loads). These switches typically
reside in one or more additional panels installed downstream from the electrical panel. Relaybased panels may also house dimmer modules as well as relay switches.
Image courtesy of Schneider Electric
CONTROLLABLE CIRCUIT BREAKERS VERSUS RELAYS
Controllable circuit breakers present advantages in:
● new buildings; and
● existing buildings where the breaker panel is not up to code.
Controllable circuit breakers are available in single-, 2- and 3-pole versions from 15-30A and
from 120-480VAC. They are robust, rated up to 200,000 switching cycles. Consolidating
electrical protection with switching in the same panel can reduce material cost while saving
wall space.
Image courtesy of Eaton
CONTROLLABLE CIRCUIT BREAKERS VERSUS RELAYS
Low-voltage relay-based systems can be advantageous when:
● the building has a code-compliant electrical panel already installed;
● a relatively small number of loads needs adding;
● single- and 2-pole relays will do the job; and/or
● the switching cycle is lower.
Relays are typically used to control single-pole 120/277VAC and 2-pole 208/240VAC circuits.
Three-pole relays are available but relatively costly compared to 3-pole controllable breakers.
Typical relays are rated from 20,000 to 50,000 switching cycles, though relays are available
offering up to 250,000 cycles. Mechanical latching operation ensures the relay will remain in
the last switched state if a power loss occurs.
Image courtesy of Wattstopper
LIGHTING AUTOMATION
Whether controllable circuit breakers or relays are used, the switch accepts input from control
devices such as a timeclock, local switches, occupancy/vacancy sensors and light sensors.
Low-voltage wiring connects these devices to the panel. The devices tell the switch to open or
close the circuit. As such, the panel can serve as the platform for a complete energy codecompliant lighting control system:
Scheduling: Panels can enact scheduling strategies to turn lights OFF in large public spaces
when they are predictably unoccupied.
Other lighting control strategies: Panels can provide switching and dimming of branch
circuits based on other control inputs such as switches and sensors.
Plug load control: Specialized switches can turn OFF 50% of receptacles based on
predicted occupancy, complying with the latest energy codes.
Other load control strategies: Some panels can control other building loads such as HVAC
systems and dampers.
Energy metering: Some panel-based systems meter energy consumption and upload data
via Ethernet connection to a central server or the Cloud for analysis using software.
OTHER CONTROL STRATEGIES
Besides achieving energy savings and energy code compliance, panel-based control systems
can deliver other value and benefits:
Strategy
How It Works
Benefits
Load preservation
Shed nonessential
loads during power
outages when
emergency power is
delivered by standby
generators
Supports emergency
power conditions such
as maintaining critical
loads
Security response
Control system
interfaces with security
system to automatically
switch lights on in
response to intrusion
alarm
Supports facility security
by supporting response
to intrusion
Building system
integration
Coordinated switching
of non-lighting loads
according to a time
schedule
Enables management
of loads such as fans,
heaters, irrigation
systems
Research/Horticulture
Tailoring lighting to
match seasonal
differences in
sunrise/sunset
Laboratory research
involving animals or
plants; plant growth in
greenhouses
SYSTEM INTELLIGENCE
Adding a microprocessor to the panel gives the control system intelligence, allowing
programming and scheduling. With an onboard lighting controller, the system operator can:
● group circuits in control zones;
● assign schedules (without needing a physical timeclock) and custom logic (IF/THEN
decision-making, called the algorithm); and
● communicate directly with other panels, computers and building automation systems
(BAS).
Panels are typically programmed at the panel’s frontboard, though Ethernet-based systems
allow remote programming via operating software.
Image courtesy of Schneider Electric
CENTRALIZED ARCHITECTURE
Panel-based systems may be centralized or distributed. In a centralized configuration, the
relays reside in a centrally installed panel. Multiple panels may install for control of single
floors or campus buildings. They may operate independently or be networked, with the lighting
controller residing in a “master” panel and controlling connected extension panels. This
provides central scheduling for all panels in a hierarchical configuration.
In a distributed configuration, very small relay-based panels (typically controlling two to four
20A circuits, see image) install closer to their controlled loads. This approach can minimize
wiring costs by reducing the length of homeruns between control devices and the panel.
System intelligence may be similarly distributed, allowing autonomous room-based operation,
though the system may allow networking of rooms.
Image courtesy of Wattstopper
NETWORKING
Networking allows data to flow between devices in a control system. Common network
options include RS-485 and Ethernet.
RS-485 is a physical layer standard governing the electrical characteristics of the sender and
receiver in a network. Economical, easy to install and resilient, it is often used for control
signaling between panels and input devices. However, it offers limited bandwidth unsuitable
for data-intensive communication such as metering.
Ethernet (IEEE 802.3), the most broadly used network IT protocol, is both a physical layer and
application layer standard, thereby able to govern communication between devices. It allows
more-intensive and higher-speed data, such as energy metering. Data can feed to a central
server or the Cloud for software- and optionally web browser-based control and data viewing.
CONNECTING THE SYSTEM
Input devices and panels, and master and extension relay-based panels, connect using lowvoltage wiring.
Standard #20 AWG Class 2 low-voltage wiring connects panels with low-voltage input devices
such as switches and sensors. Plenum-rated wire satisfies plenum and riser requirements. It
provides a dedicated path for low-voltage control signals.
Panels may be connected using data communications cabling. This type of wiring also
connects panels to digital input devices. It typically allows bi-way communication, which
enables built-in metering. Be sure to select appropriate data communications wiring and note
manufacturer limits on maximum number of connected devices and wiring length.
Image courtesy of Wattstopper
WEB-BASED CONTROL AND METERING
Panel-based systems are available that can measure energy consumption and monitor realtime voltage using metering capability built into the panel. Data feeds via Ethernet connection
to a central server or the Cloud. It then views in the manufacturer’s control software or
recognized third-party (e.g., BAS) software via a secure web browser interface.
Using this information, facility operators can measure and compare energy consumption for
different loads across buildings, departments and processes during different times of the day,
week, month, season or year. This information can provide valuable insight into optimizing
energy efficiency. It can verify performance of newly installed systems. And it satisfies
measurement and verification requirements in programs such as LEED.
The same software also allows the facility operator to change schedules and issue commands
to the control system.
Image courtesy of Schneider Electric
INTEGRATION
Integrating a lighting control system and BAS can provide greater flexibility, efficiency and
control. In an integrated system, data from a single component, such as a lighting control
device, can be used to manage the overall building systems. Conversely, a single computer
dashboard can control all building systems. Achieving this capability requires these systems
be able to share data.
For lighting and BAS to talk, they must be use the same protocol or employ a gateway
(whether a device or built-in functionality) that enables communication. The most popular are
BACnet, LonWorks and ModBus. Many lighting control and BAS systems share BACnet to
enable integration based on it being an open standardized protocol, though the designer must
understand BACnet has various dialects, such as BACnet/IP and BACnet MS/TP. Further, the
operator must decide which system will be the foundation of the integrated system, including
choices of which system’s schedules and objects to use. Some solutions partially integrate,
enabling the BAS to manage occupancy-based strategies while separating other strategies
such as daylight response.
INTEGRATION
Another strategy is to expand the capabilities of a lighting control system, as some systems
can handle HVAC, service water heater and motor loads. This might be suitable if the building
currently does not have or will not have a comprehensive BAS, and if the lighting panel will
have unused inputs/outputs. In this case, the panel can extend to provide many energy coderequired functions, such as automatic shutoff of HVAC systems and dampers.
Additionally, the panel can configure to accept control signals from other systems, such as
security systems.
EMERGENCY CIRCUITS
It is essential that the building’s emergency lighting will not be switched according to the
implemented lighting schedules, but instead operate continuously, as in the case of exit signs,
or when needed during a power failure, as in the case of emergency units.
Some panels compartmentalize emergency lighting circuits to ensure they will receive power
during a power failure and will operate when needed. Relays can be specified with normally
closed contacts to ensure continuation of electrical contact to supply power from a backup
power source during a primary power failure. Special emergency lighting remotely operated
circuit breakers are also available. To verify your requirements, refer to the Life Safety Code,
NFPA 101, as well as your state and local regulations and fire codes.
OVERRIDES
Panel-based systems often implement time scheduling as a control strategy. In this case, the
system turns OFF the lights based on what time it is, not whether a space is actually
unoccupied.
Therefore, so occupants working afterhours do not suddenly find themselves in the dark, they
should be given the capability of overriding the shutoff event and temporarily keep the lights
ON in their area. Energy codes typically limit the override period to 2 or 4 hours. For space
controls, energy codes typically limit the maximum override zone to between 2,500 and
10,000 sq.ft., depending on the code and size of the enclosed space.
Additionally, the facility operator may require the ability to override the schedule via remote
switching. In this case, the override area may constitute multiple spaces or even entire
buildings. Such overrides are important when interfacing with security and fire alarm systems.
Image courtesy of Acuity Brands
OVERRIDES
A typical local-area override is a low-voltage switch. This switch produces a control signal that
is transmitted to the panel, which controls the load. Digital low-voltage switches are
programmable and networkable. Alternately, depending on the system and desired approach,
occupants may receive the ability to override the OFF event using telephones, cell phones,
tablets or a PC.
OVERRIDES
After the override, the lights will remain ON until the next OFF event. When the next OFF
event occurs depends on the type of system. The majority of panel-based systems operate in
one of two modes.
In a sweep-based system, the OFF event occurs at a set interview during non-occupied hours
(e.g., every two hours after closing time). An occupant override simply toggles the relay or
breaker to the ON state. The relay/breaker remains ON until the next programmed sweep.
This type of system may inconvenience occupants if they initiate an override just before the
OFF sweep.
Alternately, a logic-based system can be used. In this type of system, scheduled events are
programmed, and overrides are set up with preset countdown timers. If either the schedule or
override is in a True state, the lights will remain ON. It may be possible with this type of
system to program custom configurations using special logic commands.
OVERRIDES
Although not required by energy codes, it is generally desirable to warn occupants that the
lights are about to turn OFF. For example, as long as the controlled light source is not HID,
the panel can “blink” the lights OFF and ON to warn occupants. Depending on the
manufacturer, the number of blinks and the time before shutoff may be specifiable.
Frequent switching poses a negligible effect on LED product life but may reduce fluorescent
lamp life. If fluorescent lamps are used and lamp life is a concern, alternating lamps (if bilevel
switching is employed) or some percentage of luminaires can be set to blink. If HID lamps are
used, there may be task lights or other lighting in the space that can be set to blink.
Alternately, an audible signal can warn occupants.
YOU’RE FINISHED
This concludes The American Institute of Architects Continuing Education Systems Course
EE103: Panel-Based Control Systems.
Please take a moment to provide feedback about your experience with this course.
You may also take the Comprehension Test to test your learning and to qualify for CALCTP
(CALCTP), LEU (NCQLP LC) and LU/HSW (AIA CES) credit. A 70+% passing grade is
required for LEU and CALCTP credit and 80+% for AIA CES credit.
Upon passing the test, you may download a Certificate of Completion on the Courses page. If
you are an AIA member, please email your course completion certificate to LCA with your AIA
number.