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Compact Electric Strikes

A common problem with installing electric strikes is cavity depth – that is, how deeply you need to cut into the frame (or wall) so that the electric strike will fit. For most of the twentieth century electric strikes were, and most still are, designed without consideration for this factor. Instead they are designed for burglary resistance and durability.

VD6211

Von Duprin 6211 Electric Strike

Click on  the dimensional diagram of the Von Duprin 6211 electric strike at right.   You can see that its total depth is 1-11/16 inches. All of its internal parts are heavy duty, and it has a heavy cast body and a thick, finished face plate. Most of the parts are individually replaceable. To install the 6211 in a hollow metal door frame, the dust box must be removed and often material inside the door frame – sheet rock, wood, masonry, whatever – must be removed in order to accommodate the strike. If the strike must be installed in a grouted door frame the installer is in for perhaps an hour’s worth of work that may involve a masonry drill, a 2-1/2 lb. sledge hammer, a masonry chisel and safety goggles.

HES 5000 Dimensional DrawingsIn more recent years a new generation of low profile (shallow depth) electric strikes has become available, offering unprecedented ease of installation. The HES 5000 (illustration at left) was one of the first strikes on the scene to offer a depth of only 1-1/16 inches, and advertised that it could be installed without even removing the dust box from the frame. I have found it is usually much easier to knock out the dust box for wiring reasons, but it is true that the unit will fit neatly inside most original equipment dust boxes in hollow metal frames.

More recent offerings in the shallow depth electric strike department include the Trine 3478, the HES 8000 and the Adams Rite 7440, illustrations shown at the end of this article.  All are UL Listed burglary resistant. The HES 8000 offers 1500 lbs. holding force, the 3478 offers 1200 lbs. holding force and the Adams Rite, with its innovative double keeper design, offers 2400 lbs. of holding force.  The Trine 3478 offers an install with a very tiny lip cutout, and the HES 8000 offers the advantage of needing no lip cutout at all. Each of them fit in a strike cavity only 1-1/16 inches deep.

These strikes have revolutionized electric strike installation. Before, a good installer might install six or ten electric strikes in a day. Now a really fast installer might be able to install 20 or more, greatly reducing labor and other costs associated with installation.

What’s the Trade-Off?

None of the internal parts of these strikes are available. When these strikes break, you throw them away and buy new ones. Also they do not last as long. Whereas it is not unusual to see a Von Duprin 6211 or a Folger Adam 712 still in use after 10 or even 20 years, 6 years of service is a long time for a low profile strike. In ten years you might be replacing a spring or solenoid in a Von Duprin, but you might be installing your second or third low profile strike in the same door frame in that same amount of time. This is a small inconvenience.

Upon installing that third strike in the same hole, you probably will not yet have equaled the price of a single Folger Adam 712 or Von Duprin 6211. If price up front is the primary consideration, low profile is definitely the way to go. But if in about 12 years you are installing the fourth replacement strike in the same prep, those expensive, harder-to-install, heavy duty strikes start to look like a much better value.

strikethree

HES model 8000, Trine model 3478 and Adams Rite model 7440

Thank you.

What Is A Pullman Latch?

comparisonA Pullman latch is a type of exit device latch. The leading edge of a Pullman latch, the part that hits the strike first as the door closes, is a ramp.  The back of the latch, the part that rests against the strike to keep the door latched shut, is rounded.  When the Pullman latch comes into contact with another object it retracts automatically.  It is a simple, spring-loaded mechanism.

Some rim exit devices have Pullman latches, but most concealed and surface vertical rod exit devices do not.  Most vertical rod exit devices have a main latch that is shaped like a Pullman latch but also has an additional piece that looks like a kind of separate little latch, or auxiliary deadlatch.  This part interacts with the mechanism of the latch to keep the top latch retracted until this separate piece hits the strike as the door closes.  Then the main latch pops out and locks into the strike.

Latch release extended position.

Latch release extended position.

This latch-and-release design top latch is used by many manufacturers as the mechanism that holds both top and bottom latches in the retracted position while the door is open. That way the latches do not make contact with the surfaces of the door frame, floor or threshold.  When the top latch release makes contact with the strike it releases both top and bottom latches.

The photo to the left shows the latch release fully extended and the latch fully retracted.  This is the state that this type of latch is in when the door is open.

The Pullman latch is most often used with less-bottom-rod (A.K.A. top rod only) vertical rod exit devices when they are to be used with an electric strike.  The normal latch-and-release design is incompatible with most (if not all) electric strikes. Electric strikes that are compatible with Pullman latches are said to have Pullman keepers.

Sometimes Pullman latches are used as the top and bottom latches on vertical rod exit devices because they operate more quietly than standard latches.

Pullman latches are not fire rated and are not for use with fire rated exit devices.

pullmanlatchandkeeper

Illustration of Pullman latch and Pullman keeper. Whereas the locking surfaces of electric strike keepers designed for use with cylindrical or mortise locks is perpendicular to the door frame, the Pullman keeper is at a 45 degree angle to the frame, creating an angled recess to accommodate the unique shape of the Pullman latch.


Multi-function Doorways, Part Two

Secured stairwell doors are among the most basic multi-function door applications.  In most jurisdictions they must (usually)* be both unlocked and positively latched in the event of a fire.  Unlocked so that if a person, fleeing into the stairwell during a fire, finds the stairwell full of smoke, they can safely exit the stairwell.  Positively latched so that the door will remain latched closed against the spread of the fire.

Until there is a need for access control, a passage function mortise lock, cylindrical lock with UL listed latch or exit device with passage function trim are fine.  The application begins to get interesting when the need arises to lock a stairwell door.

Right up front, electric strikes are out of the question because of the unlocked/positive latching requirement mentioned above.   It is not possible to positively latch a door when the electric strike is unlocked.  There is no such thing as a fire rated, fail safe electric strike.  If you configure a fire rated electric strike to be fail safe it voids the fire rating.

Since electric strikes are unusable for this application, that leaves either electric locks or electromagnetic locks.  Both have advantages and disadvantages.  Fail safe electric locks positively latch whereas mag locks allow the installer to us the existing hardware on the door to accomplish positive latching.  Electric locks require running wire through the door and some means of getting the wire from the frame into the door, such as an electric through-wire hinge.  Not all inspectors like electromagnetic locks, so before you install them be sure to check with your local Authority Having Jurisdiction (AHJ ) – that is, Fire Marshal or Building Inspector.

If the stairwell door already has a fire rated exit device installed, there is probably a fail safe electrified trim available for it.  Once again, this means an electric through-wire hinge or other power transfer device would be required.  Sometimes existing exit devices are incompatible with the electrified trims available for that brand and model of device.  If that is the case, the exit device might have to be replaced with one that is compatible with electrified trim.

Alternatively, there are after market request to exit (a.k.a. RX) switches available for most exit devices.  One could be used to release an electromagnetic lock on the stairwell door.

Usually it is required that all electric locking devices on stairwell doors be controlled by the fire alarm panel.  When the fire alarm is in a state of alarm, it unlocks all the stairwell doors.  Two conductor wire is run from the fire alarm panel contacts to a special fire alarm relay in the power supply that powers the electric locks on the stairwell doors.  The alarm panel opens the circuit, causing the state of the fire alarm relay to change, thus powering down the fail safe locks and thereby leaving them unlocked.

An important detail:  technically speaking, according to most building and life safety codes, fire rated doors can only be modified in a fire rated shop.  Therefore if you field cut a raceway for an electric wire through the cross members of the door, for example, you are probably voiding the fire rating.  I have never heard of anyone being called on this, but it is good to keep in mind.  Just like it is good to keep in mind that the AHJ has total authority over what you can or can’t install.  Best make sure you’re on the same page with her or him, otherwise they do have the power to make you remove what you installed and replace both door and frame to repair the damage.

Happy hardware and good luck to you.


*Some jurisdictions specify that not all stairwell doors need be unlocked in the event of a fire, only certain doors.  For example, I have known some places where code was the door had to be unlocked at every fourth floor.  Check with your local AHD to find out what the rules are for your location.


Hot Stuff: Continuous Duty Electric Locking Devices

The Ohm Symbol

I regularly hear complaints about electric strikes, cylindrical locks or mortise locks that are hot to the touch.   When I ask, I am always answered that, yes, the device is being used in a continuous duty application.

Continuous duty means that the electric lock or strike is powered continuously, usually for several hours a day.  Most fail safe locks and strikes are run continuously, since they are usually locked part of the day and they require electric power to lock.  Whenever a door is kept unlocked by using an electrical timer, the lock or strike that is controlled by the time is run continuously for part of the timing cycle.

Heat in an electric lock or strike is caused by resistance in the electrical circuit as it passes through the coil of the solenoid inside the device.  Often this heat is sufficient to “burn out” the solenoid.   The solenoid does not actually catch fire, usually.  The term, “burned out” refers to a solenoid that has been ruined by excessive heat so that it no longer functions.

Heat from electrical resistance is exacerbated when there are problems with the supply of power.  For example, if the power supply provides less than sufficient amperage to constantly power the solenoid, the solenoid will ‘run’ hotter.  Similarly if there is a current drop because of a long wire run with inadequate wire gauge, the solenoid will not get sufficient current and will run hot.  Also if the voltage supplied is significantly higher than the solenoid is rated to accept, that could create a heat problem as well.

Often, however, there is no detectable reason for the solenoid to run hot.  Sometimes, it seems, they just do.

A great way to mitigate the problem of the hot lock or strike (when all power supply problems have been solved) is to use an electrical device in line with the electric lock or strike that provides it with a full inrush voltage and current upon activation and then reduces the voltage and/or current to a holding level, allowing the solenoid to run cooler.

Several companies offer these units.  Here are some examples:

  • HES:  Model 2005M3 Smart Pack controller
  • COMMAND ACCESS:  CRU-2 current reduction unit
  • TRINE:  LC-100 line conditioner

 

 

PS900 Series Schlage Electronics and Von Duprin Power Supplies Demystified

Von Duprin and Schlage Electronics are divisions of Ingersoll Rand. Both are major manufacturers of power supplies for use with electric locking systems and access control. As of January 1st, 2011, Ingersoll Rand discontinued two of their power supply product lines, the PS800 series Von Duprin and the Schlage Electronics 500 series, and merged them into the new PS900 series.

A split in power supply branding may or may not remain, depending on what document you are looking at, but whether they say they are Schlage or Von Duprin, they are all the same PS900 series.

Here is the lineup:

PS902 – 2 Amp output at 12 or 24VDC, field selectable

Compatible with these option boards:

  • 900-BBK: Battery Backup – back up power in case of power outage, includes batteries
  • 900-FA: Fire Alarm – relay for interface with fire alarm panel  – wires to main board
  • 900-2Q: 2 Relay QEL control Board – to run 2 Von Duprin QEL devices
  • 900-4R: 4 Relay Output Board – four relay outputs to operate 4 electric locking devices, not QEL or EL
  • 900-4RL: 4 Relay Logic Board – for man trap or security interlock systems or up to 4 QEL devices
  • 900-8F: Fused 8 Zone Distribution Board – 8 outputs, fused for circuit protection
  • 900-8P: PTC 8 Zone Distribution Board – 8 outputs, circuit breaker protected

PS902 can accommodate 1 of the above option boards in addition to the 900-FA option and battery backup.

For use with electric locks and with Von Duprin Quiet Electric Latch retraction (QEL) exit devices, but NOT with Von Duprin electric latch retraction (EL) exit devices.

PS904 – 4 Amp output at 12 or 24VDC, field selectable

Compatible with these option boards:

  • 900-BBK: Battery Backup – back up power in case of power outage, includes batteries
  • 900-FA: Fire Alarm – relay for interface with fire alarm panel  – wires to main board
  • 900-2Q: 2 Relay QEL control Board – to run 2 Von Duprin QEL devices
  • 900-4R: 4 Relay Output Board – four relay outputs to operate 4 electric locking devices, not QEL or EL
  • 900-4RL: 4 Relay Logic Board – for man trap or security interlock systems
  • 900-8F: Fused 8 Zone Distribution Board – 8 outputs, fused for circuit protection
  • 900-8P: PTC 8 Zone Distribution Board – 8 outputs, circuit breaker protected

PS904 can accommodate up to 2 option boards and battery back up.

Note:  no plug-in for fire alarm relay on main board.  900-FA is only usable with the PS904 if used with an option board.

For use with electric locks and with Von Duprin Quiet Electric Latch retraction (QEL) exit devices, but NOT with Von Duprin electric latch retraction (EL) exit devices.

PS906 – 6 Amp output at 12 or 24VDC, field selectable

Compatible with these option boards:

  • 900-BBK: Battery Backup – back up power in case of power outage, includes batteries
  • 900-FA: Fire Alarm – relay for interface with fire alarm panel  – wires to main board
  • 900-2Q: 2 Relay QEL control Board – to run 2 Von Duprin QEL devices
  • 900-2RS: 2 Relay EL Control Board – to run up to 2 Von Duprin EL devices
  • 900-4R: 4 Relay Output Board – four relay outputs to operate 4 electric locking devices, not QEL or EL
  • 900-4RL: 4 Relay Logic Board – for man trap or security interlock systems
  • 900-8F: Fused 8 Zone Distribution Board – 8 outputs, fused for circuit protection
  • 900-8P: PTC 8 Zone Distribution Board – 8 outputs, circuit breaker protected

PS906 can accommodate up to 3 option boards, fire alarm interface (with option board) and battery back up.

For use with electric locks and with up to 6 Von Duprin Quiet Electric Latch retraction (QEL) exit devices, but NOT with Von Duprin electric latch retraction (EL) exit devices.

PS914 – 4 Amp output at 12 or 24VDC, field selectable

Compatible with these option boards:

  • 900-BBK: Battery Backup – back up power in case of power outage, includes batteries
  • 900-FA: Fire Alarm – relay for interface with fire alarm panel  – wires to main board
  • 900-2Q: 2 Relay QEL control Board – to run 2 Von Duprin QEL devices
  • 900-2RS: 2 Relay EL control Board – to run up to 2 Von Duprin EL devices
  • 900-4R: 4 Relay Output Board – four relay outputs to operate 4 electric locking devices, not QEL or EL
  • 900-4RL: 4 Relay Logic Board – for man trap or security interlock systems
  • 900-8F: Fused 8 Zone Distribution Board – 8 outputs, fused for circuit protection
  • 900-8P: PTC 8 Zone Distribution Board – 8 outputs, circuit breaker protected

PS914 can accommodate 2 of the above option boards, plus fire alarm interface (on one of the boards) and battery back up.

Capable of powering:

  • Up to 4 Electric Latch retraction (EL) exit devices with 900-4RL board
  • Up to 2 EL devices with 900-2RS board
  • Up to 4 Quiet Electric Latch retraction (QEL) exit devices
  • Up to 4 Chexit (CX) delayed egress exit devices off the main board (use 900-8FA combination board if Fire Alarm relay is required)
  • Electric locks or strikes

 

Ordering Tips:

PS-914 is a 4 Amp power supply that is double the capacity of the old PS873, however, from my conversation with IR tech support, their feeling is that it is prudent to power no more than 4 EL devices per PS-914.  Theoretically the power supply could support as many as 8 EL devices however this presents the challenge of timing the relays so that no two can change states at the same time.  If two EL devices are powered up simultaneously the PS-914 could be damaged.

None of the PS900 series power supplies are a drop-in replacement for their predecessors, and the old and new option boards are not cross-compatible with the old and new power supplies.  Therefore, replacing old power supplies with new can present a rewiring challenge.

Ordering back-up batteries can be a little tricky, since they have very similar part numbers for the batteries, the charging circuit board, and a set that includes the board and the batteries.

  • 900-BAT – Pair of batteries only
  • 900-BB – Battery back up board only
  • 900-BBK – Power battery back up kit, board and batteries

 

 

What’s Hot in Door Hardware

A couple of new innovative products have recently caught my attention.  Here they are:

Security Door Controls (SDC) Model LR100VDK:

Field Installed Electric Latch Retraction Retrofit Kit for Von Duprin Exit Devices

 

 

 

 

 

 

 

 

This product is available now.

http://www.sdcsecurity.com/whatsnew2.aspx#lr100

The mere 450mA inrush powering Security Door Controls’ new electric latch retraction retrofit kit is attractive enough.  Its compatibility with all Von Duprin touch bar style devices may make it just about irresistible.   Optional request to exit switch kits are available.  The unit is usable for access control and electric dogging applications.

The small inrush is huge.  (I always wanted to say that.)  High inrush electric latch retraction requires special, expensive power supplies.  Not so with the LR100VDK.  Your average regulated and filtered 1-amp 24vdc power supply will do nicely, thank you.

Another great aspect of this kit is that it is compatible with the Von Duprin 22 series exit device. So now, for relatively short money you can give a customer electric latch retraction in a decent quality exit device.

HES Model 8500 Electric Strike for Mortise Locks


http://www.hesinnovations.com/en/site/hesinnovations/Products-startpage/?groupId=141798&productId=764670

This product is due to become available by the end of August, 2011, but we’ll see.

Hanchett Entry Systems’ new lipless electric strike solution for mortise locks.

Installing an electric strike to release a mortise lock will be much easier with the HES 8500 since no cutting of the face of the frame is necessary.  Below is an illustration showing the difference between the HES 1006 standard electric strike for mortise lock and the new HES 8500.

HES 1006 prep for hollow metal

HES 8500 door prep for hollow metal - look ma, no lip!

 

 

 

 

 

 

 

 

 

 

 

 

This is not a new idea, but installers seem excited about the prospect of having an alternative to the Securitron UnLatch, which has been around for quite some time.  The Unlatch model that the HES 8500 will compete with will be the Securitron MUNL.

Of course, the advantage the MUNL currently enjoys is that, unlike the 8500, one can actually buy an MUNL.  Comparatively, the Securitron requires a door frame depth of about 1-7/8 inches whereas the the 8500 will require about 1-3/8 inches.  The 8500 will draw 240mA at 12 volts DC and 120mA at 24 volts DC and draws no inrush current.  The MUNL has an inrush of 2 amps at 24vdc or 4 amps at 12vdc and an operating current of 600mA at 12vdc or 300mA at 24vdc.  One important result of the lower current consumption of the 8500 will be that instead of the 4 amp 12vdc or 8 amp 24vdc power supply necessary for each MUNL, one 8 amp 24vdc power supply will theoretically power as many as perhaps 60 of the new HES 8500.  Of course then, factors like wire run will come into play, but still.

Another positive attribute will be that the 8500 will be field selectable for fail safe or fail secure whereas the MUNL requires an additional module to make it fail safe.

All in all, the 8500 seems that it will be a better choice all around.  We’ll just have to wait and see how it performs in the field after it becomes available at the end of August 2011.

Fail Safe and Fail Secure Electric Locking Devices

Definition

Basically:

  • Fail Safe = power off, it’s unlocked
  • Fail Secure = power off, it’s locked

Electric locking devices include:

  • Electric strikes
  • Electromagnetic locks
  • Electromechanical locks
  • Electrified exit devices

Most electric strikes are sold fail secure by default. For example,
if you order a Von Duprin 6123 24V US32D, and architectural grade 1
electric strike, it will most likely come fail secure regardless if
it has Von Duprin’s “FSE” (standing for fail secure) in the part number
or not. The part number in the Von Duprin price book does not include
“FSE.” To be sure you are going to get a fail safe electric strike (not
the norm) if that is indeed what you want, in this instance you would
include Von Duprin’s abbreviation for fail safe, “FS”, for example,
6123 -24V-FS-US32D.

All electromagnetic locks are fail safe because they are always
unlocked when disconnected from the power source. Using a battery
back-up does not make an electromagnetic lock fail secure because
the magnet would still be unlocked if the power was disconnected.
Later in this article it should become apparent why this detail
is important for reasons of life safety.

Electromechanical locks include standard cylindrical or mortise
locks that have been electrified and locks that are designed to
only work electrically, such as an electric bolt lock. They are
sold in equal amounts fail safe and fail secure.

Electrified exit devices come in a variety of functions, including
those with electric latch retraction and those with electrified outside
trim control. Electric latch retraction devices are fail secure whereas
exit devices with electrified exterior trim control might be either
fail safe or fail secure.

Application

Electric Strikes

Fail safe electric locking devices are used wherever doors must remain
unlocked in the event of a fire or other life safety emergency. If
the opening is fire rated, it must be positively latched by a fire
rated device in the event of a fire. Therefore there is no such thing
as a fire rated fail safe electric strike because if the power were
off (as it might very well be during a fire) the door would not be
positively latched. If you install a fail safe electric strike on
a fire rated opening, the inspector can require you to replace the
entire doorframe.

Technically, fire rated door frames cannot be modified in the field,
but must be prepared for hardware (including architectural grade electrified
hardware) in a fire rated shop. I have never heard of this being enforced,
nevertheless, the AHD (Authority Having Jurisdiction) could enforce
it, so if you plan to modify a fire rated opening in any way it might
be a good idea to get the local fire marshal on board during the planning
stages.

In general, a fail safe electric strike is a good choice for a “non-fire-rated
door that must be unlocked in the event of an emergency other than
a fire” kind of application.

Fail secure electric strikes are a good choice for exterior or other
non-fire-rated doors where remote release or electronic access control
is needed. They are pretty reliable, usually not difficult to install,
and relatively inexpensive. One of the chief disadvantages of an electric
strike is that, on out-swinging doors, they provide an opening into
which a burglar can insert a tool, such as a tire iron, to pry directly
on the locking device. A latch guard is a minimally effective deterrent
to this kind of attack.

(Exterior doors are almost never fire rated, and if they are, usually
it is because all the doors on the job were ordered to the same spec,
not because they have to be.)

Electromagnetic Locks

Some inspectors and fire marshals just don’t like electromagnetic
locks. This is another reason to get your local AHD on board from
the start. But if your AHD is not an obstacle, a mag can be a good
solution for existing fire rated doors with existing fire rated hardware
on them. The fire rated hardware can stay to keep the door positively
latched in the event of a fire, and the mag is inherently fail safe,
so it could be a good choice for stairwell doors, greatly simplifying
the application. The problem with mag locks is that they lock both
sides of the door simultaneously. That means you have to deal with
both a means to get in (access control) and a means to get out (presence
detector and redundant exit pushbutton, for example).

If the door already has an exit device, it is probably possible to
install a request-to-exit (RX) switch in the bar to allow exit by
a fully mechanical means – a factor which might make the AHD happier
with the installation. The AHD will also want to know that all electromagnetic
locks are wired so that the fire alarm will cut power to them in the
event of a fire.

Since a mag lock does not positively latch, it cannot be legally
used alone on a fire rated door. There must be a fire rated positively
latching mechanism in addition to the mag.

Delayed egress electromagnetic locks can also be used for access
control on egress doors while helping to prevent unauthorized exit.
For more information on delayed egress, please visit:

Electromagnetic locks are not too expensive and are very easy to
install. Because they are inherently fail safe, you may want to install
a battery back-up system so that they remain locked during routine
power outages.

Electromechanical Locks

Fail safe electrified standard locks are ideal for stairwell doors
(unless they already have exit devices) because they remain positively
latched when unlocked. Many states and localities require that stairwell
doors be unlocked in the event of a fire, and because all interior
stairwell doors are fire rated, they must also remain positively latched.

In order to replace a standard mechanical lock with an electrified
one, a raceway must be drilled through the door from lock side to
hinge side so that wire can be run to power the lock. If you guessed
that, technically speaking, this voids the fire rating on a fire rated
door, you were correct. Be sure to clear all modifications to fire
rated openings in advance with the local AHD.

Electric bolts are usually used as a last resort when no other application
will work, such as when retrofitting access control to automatic sliding
doors. Electric bolts are most commonly used in prisons, where egress
concerns are treated rather differently than commercial applications.
They can also be used in place of electromagnetic locks, however electric
bolts designed for commercial (rather than detention) applications
are less secure, less durable and more difficult to install than mag
locks.

Electrified Exit Devices

If a door has an existing exit device or an architect has specified
an exit device for an opening, it is because the capacity of the building
in terms of the number of people therein warrants the use of an exit
device. Therefore it is unwise to replace an exit device with another
kind of hardware.

Luckily, many exit devices can be electrified in the field either
by replacing internal parts of the device or by adding an electrified
trim (outside handle or lever).

As I mentioned earlier, exit devices can be electrified in one of
two ways:

  • Electric latch retraction
  • Electrified outside trim

Since electric latch retraction is always fail secure, it might not
be a good choice for stairwell doors unless it was always unlocked
from the stairwell side. If that were the case, the only probable
purpose for the electric latch retraction would be to unlatch the
door for a power operator (automatic door opener).

Electric latch retraction is ideal on exterior pairs of doors where
fail secure access control is required. Since exterior pairs of doors
are often equipped with concealed vertical rod exit devices, installing
electric latch retraction is often the easiest and best alternative.
Electric latch retraction (or electric remote dogging) is also very
compatible for use with power operators.

The down side of electric latch retraction, in addition to being
expensive in its own right, is that it often requires a special and
expensive power supply. Sargent 56 prefix exit devices are an exception,
requiring only a minimal power supply for activation.

Fail safe electrified exit device trim is a good alternative for
stairwell doors whether they already have an exit device or not. For
one thing, since the wire powering the trim is run through the exit
device, no modification of the fire rated door is necessary.

Electrified exit device trim is also available fail secure, and is
often a less expensive alternative to electric latch retraction where
simple access control is the goal.

Note on “Continuous Duty”

I have been asked, ‘What is the difference between fail safe and
continuous duty?’ Fail safe applies to the function of the device
as described above whereas continuous duty simply means the strike
is built to be constantly powered if so required. The confusion arises,
I think, because all fail safe locking devices are continuous duty.
This is because a fail safe device must have power to be locked. Fail
secure electric strikes that are connected to a timer and powered
all day to remain unlocked also must be continuous duty rated. Therefore,
not all continuous duty electric strikes are fail safe, but all fail
safe strikes are continuous duty.

Rule of thumb: almost every kind of electric locking device that
runs on DC current is continuous duty.


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