Use
Backup Power For EM Locks
Access control, one of the key components of a comprehensive security
solution, comes in many different varieties. Essentially there are two
components, the lock (i.e. the physical mechanism
keeping the door locked) and the access control system (such
as a card reader, biometric reader, keypad etc, which opens the lock).
Most locks can be set to
function in one of the following ways:
Fail-safe: in the event of a loss of power supply, the
lock will automatically unlock, ensuring that people can
still exit through the door (safety first)
Fail-secure: in the event of a loss
of power supply, the lock will automatically lock,
meaning people are unable to enter (or exit) through the door (security
first)
It
therefore only takes a loss of power to make a fail-safe lock ineffective. Of
course there can be a battery backup supply installed, but the battery will
have a limited lifespan, perhaps not more than a couple of hours, which
limits the time available for the power supply issue to be resolved. Fail-secure
locks are therefore better for doors which require higher security, but
carry greater risk for safety as there could be people trapped inside the
building.
When the
main power fails, many believe maglocks must leave doors unlocked.
However,
battery backed up maglocks are allowed according to IBC / NFPA code. It
just needs to be done properly. We examine the five critical steps for using
backing up maglock power correctly:
·
Understanding
Codes
·
Calculating
Power Budgets
·
Factoring
In Power Source
·
Connecting
Power Supply Fire Alarm Loops
·
Including
The AHJ
In this
note, we look at what the code actually says about power backups for maglocks,
where they might be illegal, and how to do it right when allowed.
Multiple Factors
When it
comes to preventing your Electromagnetic locks (mag-locks) doors from being
unsecured when power drops, there are three basic considerations to make:
·
Codes: Understanding
the applicable codes and how they apply to a building's use
of maglocks is the fundamental start.
·
Engineering:
Translating those code requirements into a compliant design.
·
The
AHJ: Getting approval from the relevant authority is the last, and maybe most
critical aspect of the process.
Codes
Accounting
for about 80% of the access control in use, mag-locks operate by an electromagnetic strip attached to the door frame
which aligns with an armature attached to the door. The lock can be fail-safe
(whereby the electromagnet releases the armature) or fail-secure (whereby the
electromagnet attracts the armature) depending on the use and safety standards.
Surprising
to many, national codes do not forbid the use of battery backed up maglocks,
despite the dominant 'free egress must always be possible' theme. If codes
indeed forbid battery backups, these exceptions are made at the local level.
However, their use is allowed if done correctly. Take a look at these passages,
covering the full scope of controlled openings regardless of occupancy code:
·
NFPA 101 (2012) 7.2.1.5.6 (Electrically
Controlled Egress Door Assemblies)
·
NFPA 101 (2012) 7.2.1.6.2 (Access-Controlled Egress
Door Assemblies)
·
NFPA 72 (2012) 21.9.1 Electrically Locked
Doors
·
IBC 1008.1.9.9 (2012)
The
fundamental relevant clause cited is:
Loss of
power to the listed hardware must automatically unlock the door.
However, the
clause does not prohibit the use of backup power. Any electric lock in the
direction of egress shall be connected to the fire alarm system and unlock when
the system is activated or when power is lost.
The local
jurisdiction may have a variation of these 'model codes' that take exception to
the rules, so maintaining local awareness of using maglocks or backup power to
them is a crucial step, often undertaken when meeting the AHJ. (See the last
section in this artical.)
Calculating Power Budgets
Knowing how long a battery will keep a maglock locked is crucial.
Maglocks are typically high demand devices that can drain batteries
rapidly as the current draw of maglock is continuous, unlike other lock
types that only use power when unlocking.
Take this example 500 pound maglock that requires 320mA at 12
VDC or 170mA at 24VDC:
Assume a 12VDC backup system furnished with two 5 amp hour
batteries that must keep four maglocked doors (two sets of double doors)
energized. The locks alone consume over 1.25 amps per hour, so with a 10 amp
supply, doors will fall unlocked in less than eight hours. As such,
prolonged outages may still require manual security response, such as guard staff
mechanically locking normally maglocked doors.
Calculating this demand is complicated by other devices that must also
be powered in the access system, typically the controllers, readers, and even
some RTE devices like PIR motion detectors. The total demand associated with
the backup supply may quickly shave the backup power duration to mere minutes
in a large system, and ample capacity is a matter of careful design.
Designing Battery Backup - Device / Door Priority
Part of
designing a battery backup system may be prioritizing specific (perimeter)
doors to stay locked, but leaving others (inside) unlocked when power drops. Of
course, the decision must conform with facility security management plans,
but in the interest of maximizing uptime for critical doors, others may need to
be excluded.
Factoring In Controller Power Support
However,
even if one specifies sufficient batteries, a door controller may not support
passing sufficient power for the period desired for battery back up power.
Normally,
the maglock will be powered by main power and power will be switched on/off by
controller contacts. However, in cases when main power fails or the
access designer connects maglocks as field-powered devices, power may then
supplied and routed through the controller itself. Flat out, many controller
contacts are not designed or rated to deliver substantial amps for long
periods.
While card
readers may draw modest amounts of power (ie: 35mA - 100mA), the controller's
output relay contacts may not be rated to pass through sufficient amperage to
power maglocks (ie: 125mA - 850mA+)
(Note:
Later versions of eIDC32 do not include this output power limitation.)
It is
because of this limitation, and the way that codes address 'direct
interruption' of power to maglocks, that most maglocks are best installed
using a separate linear power supply, not powered by pass-thru capacity in the
controller.
Batteries vs UPS vs Generators
It is worth noting that batteries are not always the only, or even
preferred method, of backup power. UPS devices or batteries, as noted in UPS
Backup Power for Security Guide, are the most unitized and least expensive to
deploy, but run duration is always a concern. As a result, especially in
critical infrastructure or services facilities, the entire building may be
backed up by a generator. In this case, the supply is generally much more
substantial and runs into hundreds of amps per hour. In these situations, the
run length of the backup system may simply not be a realistic problem.
Power Supply Fire Alarm Loops
The codes are clear on one engineering point: when the fire alarm
activates, all power to maglock must drop. This typically is implemented by
tying the linear power supply into the fire alarm via an input loop. When
the alarm is pulled, it sends a signal to the supply that it must cut power to
whatever device is wired to it.
Most access panel and maglock manufacturers include these instructions,
although they are typically vague on details in how to connect their components
so that it happens. In many cases, the install instructions state 'Installer
must wire controller and/or power supply to stop issuing power when local fire
alarm is activated', or similar. However, connection plans for doing
this are not hard to accomplish if understood graphically.
For example, take this Kisi access control knowledge base schematic that
shows this common connection graphically:
Power to the maglock is directly issued by a linear power supply, that
in turn is triggered to drop power when a fire alarm is detected at the
controller. Alternatively, the power supply itself may include fire alarm
input contacts instead of connecting to a door controller. As previously
noted, however, this power drop may apply to every device connected to the
supply: readers, controllers, RTE and more.
This may leave the door unsecured, and the main motivation of 'occupant
safety' takes a clear precedence over 'building security'. Therefore,
schematically planning out where each device is powered, and under what
conditions backup power is supplied, should not be oversimplified.
Including The AHJ
Even after
all this is done, the answer might still be "no". If the
local authority having jurisdiction, or AHJ, does not approve, the idea is
dead. There are two basic reasons why local AHJs may not accept the idea:
·
First
Responder Access: AHJs simply do not want any possibility that
firefighters cannot enter a building because the door is locked.
·
System
Malfunction: Alternatively, some AHJs refuse backed up maglocks
because if the fire alarm interface malfunctions, the batteries could
potentially keep the door locked and trap panicked occupants inside a dangerous
building.
As a result, some areas outright forbid using backup power of these
types of door locks as a matter of local exception and take any decision out of
the hands of local inspectors.
Proceed Cautiously
These
issues describe why maglocks are hated or deemed too difficult to work
with by many. While using maglocks may be less expensive or easier to install
that other types of electric locks, they are not always the best choice. If the
opening design is too restrictive or costly to employ other lock types,
then backup power must be supplied to keep doors locked.
Working
through a code compliant design and getting approval of the AHJ become a
priority for the new access system.
Before you
make any decisions about what lock is best for your site, it's important to
first think carefully about what your site requires in terms of safety and
security, and to evaluate how risk can be reduced to ensure that security
related incidents won’t interrupt your business operations.
Another
key consideration is the state of the site itself: if you are adding access
control to a site after its completion, it may be easier (and certainly more
cost effective) to opt to use wireless locks as installing all the
components and wires for mag-locks and electric strike locks will require a lot
of additional time, labor and effort.
Some
end-user opt for a combination of locks, installing a mag-lock and an electric
strike lock on a single door to ensure that it is safe, secure and is able to
accurately record movements of people in and out of the door at all times.
However, in this case, it may just be simpler and more cost effective to
install a wireless lock.
If you
still aren't sure what type of lock and access control system best meets your
needs, feel free to get in touch with one of our experts via ssaintegrate@gmail.com. Before
selecting vendor / installer check and verify they are authorized or not to
execute your access control system.
