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Interconnected Locks


Sargent 7500 Series Interconnected Lock

An interconnected lock is actually two locks that are connected by an assembly that retracts both the deadbolt and the latch simultaneously when the inside handle is turned.   This is done to fulfill the life safety requirement under NFPA 101 that egress should be accomplished by one motion with no prior knowledge necessary, and at the same time provide the user with the security of a deadbolt.  The same function could be provided by an entry function mortise lock, but interconnected locks are cheaper, since they are usually cobbled together out of (usually) a grade 2 cylindrical lock and a tubular deadbolt.

The history of the interconnected lock is a twisted, strange story of different companies reinventing the wheel with different distances between the centerlines, connected or separate latch/bolt assemblies with correspondingly different strike preps, and radically different hole patterns on both interior and exterior door surfaces.  The end result has been many, many doors and frames prepped for locks that are now irreplaceable.

Today, preps are much more standardized.

These are some of the interconnected locks available today and the measurements of their preps:

  • Falcon H Series – 4 inches CTC, 1-3/4 inch hold above, 2-1/8 inch hole below
  • Schlage H Series – 4 inches CTC, 1-1/2 inch hole above, 2-1/8 inch hole below
  • Schlage S200 Series – 4 inches CTC, 1-1/2 inch hole above, 2-1/8 inch hole below
  • Schlage CS200 Series – 4 inches CTC, 2-1/8 inch holes above and below
  • Sargent 75 Series – 4 inches CTC, 2-1/8 inch holes above and below
  • Yale 4800LN series – 4 inches CTC, 2-1/8 inch holes above and below

Replacing any of the locks above with any of the others would not present an enormous problem.


Sargent 7500 Series Door Prep

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
  • 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


    Deadbolts and Auxiliary Deadlocks


    There are three main types of deadbolts:

    • Tubular (or Cylindrical)
    • Rim (surface mount)
    • Mortise

    This article discusses the installation details and relative merits of each, as well as what to look for in terms of quality and security.

    Deadbolts are usually considered an auxiliary lock because, with the exception of aluminum and glass storefront doors, they are not the primary means of latching the door shut.

    Tubular Deadbolts

    Above is a the first page of the B600 Series section of the Schlage commercial price book, showing an exploded view of the B600 series deadbolt.  Notice the “Security Shield” that protects the bolt from attack through the door.

    Tubular (or cylindrical) deadbolts are by far the most popular deadbolts used today.   Preferred by renovation contractors for their ease of installation, they differ greatly in quality and security.


    Tubular (or cylindrical) deadbolts are generally installed into a modified 161 door prep – that is, the same prep that accepts a standard cylindrical doorknob or lever set.  The 161 prep consists of a 2-1/8 inch diameter hole drilled through the door.  This hole is called the “bore.”   A second hole, called the “cross bore,” is then drilled from the lock edge of the door to intersect with the bore.  This second hole is usually 7/8 or 1 inch in diameter and is located on the center line of the first hole.  See diagram:


    Quality and Security

    Quality in tubular deadbolts ranges from the relatively poor quality of inexpensive locks widely available in lumber yards and hardware stores to high security versions available mainly from locksmiths and other security hardware specialists.  The differences between cheap and good are:

    • Sturdiness of the bolt
    • Strike reinforcement
    • Guarding of the bolt
    • Sturdiness of the cylinder collar
    • Bump, pick and drill resistance

    The bolt is the actual part that projects out of the door and into the door frame.   The sturdier it is, the harder it will be for a burglar to break it off or saw through it.

    The strike, or strike plate, is the rectangular piece of metal in the door frame that receives the bolt.  In a wooden frame, this piece will only be as strong as the wood it is attached to.  This is why it is important that the strike fasteners are long enough to reach the stud behind the frame.

    The dust box goes inside behind the strike plate, inside the door frame.  A metal dust box makes it much more difficult to get a tool behind the end of the bolt – a very important function in terms of burglary resistance.

    On a steel door frame the strike plate becomes less important, but it is still important to guard the end of the bolt as effectively as possible.

    The cylinder collar is the washer-like ring that surrounds the cylinder and rests against the exterior surface of the door.   The best deadbolts have solid collars that spin freely if one tries to twist them off with pliers.   Cheap deadbolts have hollow collars that crush like a beer can when gripped by pliers.

    Since key bumping videos are now widely available via the Internet, it is worthwhile making sure your locks are bump resistant; lock picking is more of an art, but some burglars are skilled in it, so pick resistance is worth having; and because cordless drills are inexpensive and readily available, drill resistance is a good thing, too.   Locks that are resistant to these three kinds of attacks have a UL Listing UL437 for Burglary Resistance and say so on their labeling.  Two deadbolts that offer UL437 burglary resistance as well as sturdy bolts, collars and provisions for strike reinforcement are the Schlage B600 series with Primus or Everest UL437 cylinder, and the Medeco D11 series with M3 series cylinder.

    Rim Deadlocks

    The terms “deadlock” and “deadbolt” are often used interchangeably.

    Surface mounted deadbolts, AKA rim deadlocks, were once the industry standard.   Many locksmiths’ fortunes were made on the Segal 667 “jimmy proof” deadbolt with cylinder and latch guards, and, in fact, that locking system was often effective in keeping burglars out.  My personal preference for maximum locking strength (short of a multi-point lock) is a jimmy proof rim deadbolt and a tubular deadbolt on the same door.

    Here is an illustration of the Segal vertical deadbolt:

    A jimmy proof deadbolt, otherwise known as a vertical deadbolt, is the most effective kind of rim deadlock because it interlocks the door and frame in a way that few other locks do.

    The other kind of rim deadlock is a horizontal deadbolt such as the Yale 112 (see below left).

    The Yale 112 features a 1-1/2 inch throw deadbolt – ½ inch longer than what is normally available in a tubular deadbolt.

    To achieve bump, pick and drill resistance in a rim deadlock, simply add a UL437 UL listed rim cylinder.  Protect the cylinder with a cylinder guard to increase security still further.

    The weakest part of the rim deadlock is the strike when it’s installed into a wooden frame.  To help alleviate this weakness, install screws that are long enough to reach the stud behind the door frame.

    On a metal frame, a rim lock strike can be very strong when it is installed correctly.

    Mortise Deadbolts

    There are two kinds of mortise deadlocks:

    • Small Body Mortise Deadbolts
    • Full Size Mortise Deadbolts

    Small body mortise deadbolts are usually installed where most auxiliary locks are installed, six inches to a foot above the primary lock, maybe around 60 inches from the bottom of the door frame.  The lock case of a small body mortise lock is variable – that is, it is not standardized.

    A small body mortise deadbolt can be a good choice for a wooden door, especially if it is a thicker-than-usual wooden door.  Since the lock is a good size metal box that gets tucked into an approximately 5 inch by 1/2 inch pocket carved into the wood, the lock utilizes the strength of the door to its best advantage.

    Full size mortise deadbolts are installed in an “86 prep” (see illustration), which is a pocket located on a center line about 40 inches above the bottom of the door frame.  Unlike most other deadbolts, full size mortise deadbolts are intended for use as the primary – and usually the only – lock on any given door.  Full size mortise deadbolts are usually used on mechanical compartments, closets in corridors or other places where trim would be in the way.

    Both small body and full size mortise deadbolts feature heavy duty mechanisms and strong, 1-inch projection bolts.  With the addition of a high security, UL437 UL listed mortise cylinder to add bump, pick and drill resistance, mortise deadbolts can provide a high degree of security.


    Schlage L460 Series Small Body Mortise Lock


    Understanding Door Security Monitor Switches

    A number of different kinds of switches are available to help you keep track of whether or not your door is shut and / or locked.  Here are some of them:

    Door Status Monitor Switch

    A door status monitor switch changes states when the door is opened or closed.  Typically this is accomplished by using a magnetic reed switch, either surface mounted or concealed in the edge of the door and door frame like the one shown at right.

    How a Magnetic Reed Switch Works

    The magnetic reed switch is typically installed on the door frame and the magnet that activates the switch is typically installed on the door.   Inside the magnetic reed switch, a thin piece of steel – a steel ‘reed’, if you will – is held in position by the attraction of the magnet when the door is closed.  When the door is opened, the magnet is taken away from the switch and the spring tension of the “reed” causes it to spring back against the other contact, changing the state of the switch.

    Most magnetic reed switches are normally closed – “closed loop” – but are also available normally open (“open loop”) SPDT (single pole double throw, or “form C”) or DPDT (double pole double throw).

    The Purpose of the Door Status Monitor Switch

    The door status monitor switch is used to notify remote devices that a door is open or closed.  Typically these remote devices are burglar alarm panels or access control system controllers.   It does not tell you if the door is locked, just if it is closed.

    Request to Exit Switch

    The request to exit switch, also known as a REX switch, is so named because it is usually connected to the request to exit contacts on an alarm panel or access control board.  It is used to notify an external device that someone is exiting through, or wants to exit through, a door.  REX switches come in a wide variety of configurations, from push button palm switches engraved “push to exit” to switches concealed inside exit devices.  A motion exit sensor is also a form of request to exit switch.

    Request to exit switches are available with a wide variety of contact configurations and with or without electronic or pneumatic time delay.   If the switch is being used as a means of egress for pedestrian traffic, it will need to comply with life safety code.  Life safety code varies from locality to locality as governed by your local AHJ – Authority Having Jurisdiction – that is, your local building inspector or fire marshal.

    Latch Bolt Monitor Switch / Strike Monitor Switch

    I write about Latch Bolt Monitor (LBM) switches and Strike Monitor Switches because they somewhat overlap.  Both are designed to monitor the position of the latch bolt.

    Some LBM switches are inside locks and others are in electric strikes.  From inside the lock, they monitor whether the latch is extended or depressed.  When located in an electric strike, they monitor whether or not there is a latch bolt present in the keeper.

    Pictured at right is Securitron’s line of inexpensive strike monitor switches as examples of strike monitor switches.  Several companies offer like products.  Strike monitor switches are an easy way to monitor if there is a latchbolt (or some other object) present in the keeper.   Several companies, such as Von Duprin, offer heavier duty monitor strikes.  Monitor strikes are sold as a finished unit that includes as strike and a switch whereas strike monitor switches are aftermarket add-on units.

    Magnetic Bond Sensor / Bond Sensor

    Magnetic bond sensor and bond sensor options refer to electromagnetic lock applications.  Many manufacturers offer Bond Sensor or Magnetic Bond Sensor as an option.  What this does is allow an electromagnetic lock to notify some external device that its holding force is below spec.  Authorities are alerted and the situation is addressed.

    Maximizing Effectiveness

    To maximize effectiveness of door monitor switches, it is best to use both a door status monitor and some kind of lock status monitor as well, and this is why:  because monitor switches can be fooled.  A door status switch will tell you if the door is open or closed – unless it has been altered to tell you the door is closed when it is not.  Also, a door may be closed, but not locked.  If you have a latch bolt monitor or magnetic bond sensor in place as well as a door status switch, you will know if the door is closed but not locked.

    This is the center of this knowledge:  to know that the door is shut AND locked.




    How to Choose a Door Closer

    To intelligently choose a door closer for your application you have to know certain facts:

    • Does the closer need to comply with ADA opening force guidelines?
    • Is the door an interior or exterior door?
    • What is the door width?
    • Will the closer be mounted on the push or pull side of the door?
    • Where on the door will the door closer be installed?  How much room is there?
    • Are there any special circumstances like wind, positive or negative pressure, etc.?
    • You may also need to know the door handing.

    ADA Reduced Opening Force Guidelines

    American Disabilities Act (ADA) reduced opening force restrictions are enforced by the Authority Having Jurisdiction in your locality.  In some localities or applications ADA requires a maximum opening force of 5 lbs. and in others a maximum opening force of 8.5 lbs.  Most closers on the market today can be field adjusted to comply with these restrictions, but to do so you need to have a door pressure gauge.

    I am mildly acquainted with two door pressure gauges.  One is the model DPG by HMC and the other is the ADA/FG by LCN.  Apparently there are a lot of initials involved in door pressure.

    Door closers are also available with reduced opening force meant specifically to comply to ADA standards.

    Manufacturers usually print a disclaimer that says that a door closer adjusted to ADA maximum opening force may not have enough power to shut the door.  This is often true because perhaps recommended spring strengths for different applications are the result of perhaps a century of innovation.  Manufacturers know that a force greater than 8.5 pounds may be necessary to close a door.

    Interior versus Exterior

    When speaking about door closer closing force, we say that a door closer is of a certain size.  Door closer size does not refer to actual dimensions, but to spring strength.  Historically, door closers are available in sizes 1 through 6 – 1 being the wimpiest and 6 capable of exerting the strongest closing force.

    A size 4 closer is usually recommended for an exterior, 3-foot wide door, whereas a size 3 closer is deemed appropriate for an interior door of the same dimensions.  The assumption here is that the exterior door is more likely to be expected to close a door against a wind or negative or positive air pressure.

    Door Width

    If you look at a door hung on butt hinges and equipped with a door closer from above, it looks something like this:

    View from the Ceiling


    You see from the illustration that the door closer closes the door by exerting force on a point about eight or ten inches from the hinge side of the door.  To see what this means, go to a door with no door closer.  Open it.  Now put your hand a foot from the hinge side of the door and push it closed.  Pretty difficult, isn’t it?   If your door was wider, it would be even harder to close from that point.  This is why door closer size – that is, spring strength – is determined by the width of the door rather than the height.

    For a three foot wide exterior door, you would normally adjust your door closer to be a size four.  For a four foot wide exterior door you would adjust your door closer to be a size five.  Therefore, if you have a four foot wide exterior door, you had better buy a closer that can be adjusted to a size five.

    Push or Pull?

    Different arms are required for different applications.  On doors that swing out, where the closer is mounted on the push side, the closer is mounted in a top jamb or parallel arm configuration.  If it is mounted on the pull side it is mounted in what is called a ‘standard’ installation.  (There are other ways to mount a closer on the push side, but parallel arm and top jamb are the most common.)

    See manufacturer’s literature for more information, or check out my article on Door Closer Basics.


    If you have a glass and aluminum storefront kind of door, you may have a space issue as regards your choice of door closer.  If you have a hollow metal door with no window hung in a steel frame, chances are you will have no space issue.

    You need to figure out what door closer will fit.  To do that, measure the space where you would like to install it and download installation templates or instructions from manufacturer’s web sites.  Check the dimensions to see if the closer you have selected will work or not.

    Or you can measure your door and frame and consult a door hardware professional.

    Special Circumstances

    I have installed door closers in some fairly challenging environments.  One, for example, was on a four foot wide, eight foot high, two and a quarter inch thick mahogany and glass door.  In addition to the size of the door, the location was also challenging – right across Beacon Street from the Boston Common where the wind could race across the open ground and dash itself against the door to its heart’s content.  Also, the front of the building had settled over the century or so of its existence, and leaned decidedly inward.  The door opened inward, and, left on its own, would swing sedately inward to 90 degrees if not latched.

    In other words I had to install a door closer that would close an extra heavy door, uphill, in a wind.  I actually got one that would do it about 95% of the time.  For this application I chose the most durable, powerful, adjustable door closer I knew at the time:  the LCN 4041.  If I did the same job today I would probably choose an LCN 4011 or a Norton 7500.

    A big, beefy, versatile door closer is not a cure-all.  For example, sometimes the 4041 is just too big, or templated too close to the hinge.  The point is that you must look at all the details of your door before you buy a door closer – not only how it is made and its size, but its environment as well.


    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.

    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

    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.

    Alphabetical Index


    Low Voltage Detective Work


    Finding the Current Drop


    As electric locking systems become increasingly complicated, troubleshooting these systems has also become more complex.  Yet certain basic principles always apply.

    Case in point, a customer had access control on a stairwell door using a fire rated mortise exit device with an electrified mortise lock.  The solenoid in the mortise lock had burned out twice and the third one, newly installed, was already too hot to touch.  Granted, a solenoid operated fail safe device used in a continuous duty application will get warm, but it should not get too hot to touch.  So they called me to help them figure out what was going on.

    To find the problem, I first listed the possibilities:

    1. They had gotten three defective solenoids in a row
    2. The power supplied is the wrong voltage – if the voltage was either too high or low, that would cause the solenoid to heat up
    3. The current supplied is inadequate – the solenoid used 330mA.  If it were being supplied with only 150mA, for example, the solenoid would heat up.

    We determined that 27 volts DC was available at the door to power the 24 volts DC solenoid – perfectly acceptable – and we all felt that it was rather unlikely that they had received three defective solenoids in a row.  So that left current drop.  Where was the current going?  What was preventing it from getting the current it needed?

    The access control tech on site could not determine whether the solenoid was getting enough current at the door by using a meter (for whatever reason) so we traced the current back through the line.

    The power supply was a 6 amp, 24 volts DC power supply that had an output board with 8 fused outputs.  If all were in use, then a max of 750mA should be available from each output, provided they all were carrying the same amperage load.  We determined that four of the outputs were being used:  three were used to power electric strikes at 300mA and one was used to power the electric mortise exit device at 330mA.  The sum of the current draw for all devices attached to the power supply was therefore about 1.2 amps – well within the power supply’s capacity.  Therefore the power supply size was not the problem.  The technician measured the output from the contacts that were connected to the mortise lock and found that they were outputting correct voltage and current.  Therefore the output board was not the problem.

    Assured by the technician that the wire run between the power supply and the mortise lock was less than 100 feet and that 18 gauge wire was used, I knew that the wire run was not the problem.  I asked how power got from the door frame through the door and into the mortise lock.  The technician responded that power transfer was accomplished by use on an electric hinge.

    Typical wire gauge in an electric hinge is 24 gauge – a thin wire to be sure, but since power only needs travel a few inches through it, hinge wire gauge is usually not a problem.  But this electric hinge had its own 3-foot wire lead threaded through a raceway in the door to the mortise lock.  Whereas a few inches of 24 gauge wire might not be a problem, I reasoned, three feet of it might be a problem.  We talked about it briefly and then agreed that they would give it a try.

    To my dismay, they called back two hours later – after they had replaced the wire running through the door with 18 gauge wire and let the mortise lock run on it for a while – and let me know that this did not work either.

    The answer finally came when I asked how the electric mortise lock was connected to access control and was told there was a controller in a box above the door.  The controller used a form C relay to turn the electric mortise lock on and off.  I suggested that the technicians check the relay to make sure it was working properly.  When they did they discovered that the electric mortise lock had been connected in series with another device.  This other device – whatever it was – drew enough current to deprive the mortise lock of the current it needed to operate without burning up.  Problem solved.

    The moral of the story is that, yes, access control has only gotten more complex as time goes by, but by using simple, logical methods a good technician and figure out and repair most problems.  So stick with it and keep asking questions until you ask the right one.


    And good luck!



    Door Propped Alarm


    The purpose of a Door Propped Alarm is to sound an alarm when a door has been left open after a pre-determined period of time – a function that is deceptively complex.   The motivation for this function is usually that a door is left unlocked or open when it should be closed and/or locked.  Many access control systems include Door Propped Alarm capabilities, but stand-alone Door Propped Alarms are also available.

    First, to clear up a common misconception, a Door Propped Alarm is not an exit alarm.

    An exit alarm is a relatively simple device that screams when a door is opened.  Usually it is equipped with an audible local alarm, a cylinder, keypad or credential reader for reset and authorized bypass, and a door position switch to tell the alarm when to scream.  In recent years the exit alarm has grown more sophisticated, incorporating timers for automatic reset, delayed arming and other complex functions.

    A Door Propped Alarm must accomplish a more complex set of operations because of the variety of user needs and expectations.  A lot of this variety stems from vocabulary issues.  For example, many users will refer to a door as being “closed” when they really mean, ‘locked.’  A true Door Propped Alarm will have the flexibility to accommodate these varied expectations.


    The condition that creates the need for a Door Propped Alarm is the need to leave the door open for a period of time, but no longer.  For our discussion, we’ll call this period of time the Authorized Open Period.  This is the most important time segment a Door Propped Alarm needs to track.

    The next time segment that a user may want the Door Propped alarm to track might be what could be called the Pre-Alarm state.  Typically in this state the Door Propped alarm will change the state of one or more relays.  These relays can be used to notify other equipment to create a warning sound, lock other doors, or for many other functions.  The warning sound is useful because it allows the user to close to door before the Door Propped Alarm goes into full alarm.  In the Pre-Alarm state, the Door Propped Alarm could be set up to automatically reset when the door is closed and/or locked.

    The Alarm State may or may not be a timed function, that is, it may have the ability to self-reset after a pre-programmed amount of time that would begin when the door is closed and/or locked, or it may require manual reset at the door by key or other credential.  In the Alarm State, the Door Propped Alarm may have an on-board siren or may change the state of a relay to sound an external alarm.

    Necessary Switches

    In order to work, a Door Propped Alarm needs a door status switch.  Depending on what the user wants the Door Propped Alarm to do, it also may need a lock status switch.  If the user wants to sometimes leave the door open or unlocked without the alarm going off, some kind of secure access control, such as a key switch, keypad or credential reader, will be necessary to temporarily bypass the Door Propped Alarm.  If the user wants to require that the alarm be silenced and reset at the door for extra security, a key switch or other secure access control will be needed.

    To get an even better idea of the functionality of a Door Propped Alarm, go to Securitron’s web site and search out the installation instructions for their DPA-12 or DPA-24 Door Propped Alarm.


    Exit Devices with Electric Latch Retraction


    Almost all exit device manufacturers offer the option of electric latch retraction on their touchbar-style exit devices.  Different manufactures may call it by other names such as ‘latch pull-back’ or ‘remote dogging’.  Some people refer a device with electric latch retraction as an ‘electrified exit device’, but that could also refer to electric unlocking of outside trim – a different animal altogether.  Electric latch retraction is accomplished by unsing a powerful solenoid or electric motor to actually retract the latch or latches of an exit device.

    The advantages of electric latch retraction over other means of electrically unlocking exit device-equipped openings are:

    • Electric latch retraction is fail secure.  When power is supplied, the latches retract.  When power is shut off, the latches extend, securing the door.
    • Electric latch retraction works well with power operators because when the latches are retracted, the doors can swing free.
    • With electric latch retraction, pairs of doors continue to be latched top and bottom.

    Cheaper alternatives, such as using an electromagnetic lock or an electric strike, would result in double doors that are only locked at the top.  If they happen to be aluminum narrow stile doors locked only at the top, a person could actually pull the bottom of the locked door open several inches with very little effort.  Such installations are at best sloppy, at worst not secure.

      Following are examples of electric latch retraction devices by different manufacturers.

      Adams Rite

      Division of Assa Abloy.

      Adams Rite makes hardware primarily for aluminum-and-glass storefront type doors, but also for standard hollow metal and wood doors. All of their exit devices are available with latch retraction.

      Their rim devices, the 3700, 8700 and 8800 series require no specific power supply. 12VDC models draw 1.5 amps, 24VDC models draw 600mA.

      All other devices draw an inrush current of 16 amps and require the Adams Rite PS-LR power supply. The PS-LR will power up to 2 Adams Rite exit devices with electric latch retraction.

      They make rim, concealed vertical rod, surface vertical rod, and mortise exit devices.

      They do not offer a retrofit kit for field conversion of existing devices to my knowledge.


      Division of Ingersoll Rand.

      Doromatic makes exit devices primarily for aluminum storefront doors. All of their touchbar-style devices are available with electric latch retraction. Since purchased by Ingersoll Rand they use the Von Duprin type solendoid for latch retraction, and use the Von Duprin PS873-2 power supply to handle the 16-amp inrush current these solenoids draw.

      The PS914-2RS  will power up to 2 exit devices with electric latch retraction.

      Doromatic offers an electric latch retraction field retrofit kit for their 1490 series concealed vertical rod device and their 1590 series rim device. The EL1690 concealed vertical rod device and EL1790 rim device are in fact field retrofit kits to electrify the 1990 and 2090 series crash bar “pipe-type” exit devices for latch retraction.


      Division of Stanley.

      Precision makes exit devices for hollow metal, aluminum storefront, and wood doors, fire rated and non fire rated. All touchbar-style exit devices are available with electric latch retraction. ELR devices require an ELR150 series power supply. Use:

      • ELR151 for 1 ELR exit device
      • ELR152 for 2 exit devices
      • ELR153 for 3 exit devices
      • ELR154 for 4 exit devices

      Precision offers ELRK and NELRK series conversion kits to retrofit existing exit devices to electric latch retraction in the field.


      Division of Assa Abloy.

      Sargent offers a very wide variety of exit devices in various functions and configurations to accomodate diverse applications. All 80-series models are available with “Remote Dogging / Latch Retraction”. Sargent recommends the Securitron BPS-24-1 power supply, a simple 1-amp, 24VDC power supply, to power it electric latch retraction offerings.

      Sargent offers a retrofit kit to convert existing Sargent exit devices to electric latch retraction in the field.

      Von Duprin

      Division of Ingersoll Rand.

      Von Duprin offers electric latch retraction in rim, surface vertical rod, concealed vertical rod, mortise, and three-point exit devices for narrow stile aluminum storefront, standard hollow metal, and wood door applications. These would be the 33, 35, 98 and 99 series. Like the Doromatic exit devices discussed earlier, since they use almost exactly the same solenoid, Von Duprin electric latch retraction devices draw a 16-amp inrush current and therefore require the PS914-2RS to power 1 or 2 devices.

      Von Duprin offers retrofit kits to field convert existing exit devices to electric latch retraction.

      Global Considerations

      • Check door width. Electric latch retraction devices may not fit if the door is too narrow.
      • A means of getting current from the door frame into the device, such as a door cord or electric power transfer will be needed.
      • Voltage drop due to length of wire run could be an issue with high current inrush devices.

      If you have further questions, don’t hesitate to contact me at