Knowledge is Power
Information is essential in selecting the appropriate power supplies
- By Paul Rizzuto
- Apr 02, 2008
It is critical to calculate the power
requirements of every system product
and consider how they integrate
with each other to ensure that the
selection and installation of power solutions
are appropriate for a project. This
information is necessary when selecting
the power supplies required to keep the
system running efficiently over time. To
initiate the selection process, three fundamental
areas should be addressed:
Approvals. Are there any specific
agency approvals that the installation must
meet? Each state, county and even municipality
has its own requirements regarding
agency approvals. Compliance issues such
as UL listings for video, access control
and fire/life safety must be adhered to,
along with specific local codes.
Features. Before starting the design,
a comprehensive analysis of the facility’s
security systems is required to determine
feature sets of the power supplies. Until
recently, selecting power supplies often
required combining various components
to deliver the functionality desired. All
that has changed with the introduction of
a new breed of integrated power solutions
that delivers both cost and installation
advantages.
Devices. How many devices are in the
system, and what are the power requirements
and physical location of each? This
information is a must to determine the
size and quantity of the power supplies,
how many devices they will run and
where they will be located. A good rule of
thumb is to add 20 percent more power to
your calculations as a safety factor.
Fire Alarm Systems
Power consumption is a primary issue
when configuring fire alarm systems.
One of the most critical considerations
centers on how alarm signals are activated.
When an alarm occurs, notification
appliance circuits are output from the fire
alarm control panel to activate notification
appliances, such as strobes and
horns. The number of appliances to be
activated, along with the current draw for
each device and its distance from the
FACP, sometimes makes the deployment
of NAC power extenders a necessity.
In large commercial installations or
multitenant buildings, the total current
draw of the notification appliances may
exceed the power output of the FACP. In
these instances, one or more NAC power
extenders needs to be installed for notification
appliances with wire runs that are
too long for the FACP to deliver sufficient
power.
NAC power extenders are available
with programmable features that maintain
horn and strobe synchronization by
producing internally generated sync protocols
used by major signal manufacturers
or by electronically repeating these
sync protocols from the FACP outputs.
Access Control Systems
Access control systems manage ingress
and egress at a facility by means of controlled
locking devices. NFPA requires
that any device or system intended to lock
or unlock exits must be connected to the
facility’s fire alarm system so all doors
will release when an alarm is generated.
To comply with NFPA requirements,
there are two classifications of locking
devices: fail-safe and fail-secure. Failsafe
locking devices, such as magnetic
locks, release when they lose power. Failsecure
locking devices, such as electric
strikes, unlock when power is applied and
may be manually released from inside.
This determines the manner in which the
power solution removes or provides
power, as well as the sequence and timing
of each action.
Access control power supplies come
in AC and DC versions, and some provide
multiple voltages simultaneously.
Features include independently triggercontrolled
fail-safe/fail-secure outputs,
power supervision, battery charging and
fire alarm interface. Wall- and rackmount
models are available.
Some systems also may require the
installation of panic hardware devices.
Upon activation, the devices’ high-current
power demand can reach up to 16
amps, but not all power supplies can
handle these high inrush currents. As a
result, users need to specify a power
supply designed for this type of application.
Some operate a single panic hardware
device and require optional modules
to add features like timing functions
or output relays. These base
models almost always require extra
modules to deliver the necessary func tionality and may not be cost-effective.
More advanced models offer integrated
features and supply a comprehensive
solution.
Video Surveillance Systems
Video surveillance systems typically run
all the time, placing high demands on
power supplies. These video power supplies
need to deliver a clean and consistent
source of 24-volt AC or 12-volt DC
power for uninterrupted operation.
Depending on the video component’s
power requirements and location, a selection
of power supplies is available. They
can be wall- or rack-mounted, designed
for use indoors or outdoors and feature
AC or DC outputs. Configurations range
from one to 32 outputs, and some models
offer additional features.
Other variables to consider when
selecting video power supplies include
the following:
Environmental conditions. Temperature
differences can directly affect the
performance of both the video components
and the power supply when located
outdoors. Enclosures for outdoor power
supplies should be rated to withstand the
elements.
Ground isolation. In some cases, cameras
are not equipped with internal electrical
isolation. If this is the case, it’s important
to use a power supply with this feature.
Video transmission systems. The
introduction of UTP transceiver hubs
with integral camera power makes it possible
to transmit both video and data via
structured cable along with power for the
cameras. This is accomplished via video
balun/combiners that pass the power and
data to the camera and send the video
back to the head-end equipment.
An Integrated Solution
New devices provide system designers
with a highly integrated solution. The
unit transmits UTP video, RS422/RS485
data and power over a Cat-5 (or higher)
structured cable. Features include eight
camera channels in a 1U EIA 19-inch
rack-mount chassis, video transmission
ranges up to 3,000 feet per channel, and
compatibility with AC and DC fixed or
PTZ cameras.
An optional HubSat4S Passive UTP
Transceiver Hub with integral camera
power also can be used to transmit video
from up to four cameras over a Cat-5 (or
higher) structured cable back to the
HubWayLD8S. This new breed of integrated
device reduces the time and
expense of configuring and installing
each component while minimizing bandwidth
requirements
for large systems.