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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!



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

    Exit Device, Panic Hardware and Crash Bar Basics


    The terms “crash bar”, “panic hardware” and “exit device” all mean the same thing.

    Precision Apex 2000 Series Rim Exit Devices by Stanley

    Exit devices are used on doors in the path of egress in buildings built to accomodate numbers of people.  Facilities like schools, hospitals, goverment buildings and large residential buildings all use them.  Fire rated exit devices are used on fire rated doors.  Most interior doors that require exit devices, especially stairwell doors, are fire rated.

    Fire Rated Exit Devices

    Fire rated openings require fire rated exit devices. Fire rated devices are so designated by Underwriters Laboratories. I am told that UL tests them by mounting the device on a fire rated door and setting the door on fire, letting it burn for a time, and then blasting the door full blast with a fire hose. If the door opens, the device fails the test and cannot be sold as a fire rated exit device.

    Non-fire-rated exit devices are used mainly on exterior doors.

    Dogging Feature

    One of the chief differences between a fire rated exit device and a non-fire-rated exit device is called the “dogging” feature. A dogging feature allows the user to “dog the bar down” using a hex wrench or standard key, leaving the door unlatched. Since fire rated devices must always postitively latch, they never have a dogging feature.

    Narrow Stile Exit Devices

    The term, “lock stile”, refers to the part of a panel door or aluminum-and-glass storefront door onto which an exit device or other lock is installed. Many aluminum storefront doors one encounters in the world have lock stiles only 1-3/4 inches to 2 inches wide. If you need an exit device for such a door, you need an exit device for a narrow stile application.

    Exit Device Types

    The four main types of exit devices are:

    • Rim
    • Mortise
    • Surface Vertical Rod
    • Concealed Vertical Rod
    • Mid-panel

    See examples of rim exit devices at:


    See an example of a surface vertical rod device at:

    See an example of a mortise exit device at:

    See an example of a concealed vertical rod exit device at:

    Specifying Exit Devices

    Exit device choice is based upon the door. As mentioned previously
    if the door is fire rated, the exit device must also be fire rated.
    If the door is a narrow stile door, an narrow stile application exit
    device is required.

    In addition, you need to know the width of the door. Exit devices
    come in different lengths to accomodate different door widths, so
    that the touchpad of the exit device provides the coverage required
    by national and local life safety and/or fire code. Door thickness
    could also be a factor, especially if you are going to need exit device
    trim, that is, a lever, doorknob or thumbpiece that allows people
    to unlatch the door and enter from the outside. I will discuss exit
    device trim shortly.

    For a pair of doors (otherwise known as a double opening, or a set
    of double doors), the best choice is usually a surface or concealed
    vertical rod exit device. In this case you also need to know the door

    It is possible to lock a pair of doors using one rim or mortise exit
    device and either a vertical rod exit device or a set of flush bolts,
    but these solutions (while perhaps saving a little money) present
    other problems. If you use a rim device on the active door, then the
    strike (the part you will be mounting on the inactive door to receive
    the latch of the rim device) is called quite appropriately a “pocket-ripper”
    strike, since it hangs into the opening at pretty much trouser pocket
    level. Use of a mortise exit device on the active leaf eliminates
    that problem, but it will not work as reliably as would two vertical
    rod devices, and would save very little money.

    The choice between concealed and surface vertical rod exit devices
    should be a simple one. If you are having doors made, have the door
    manufacturer install concealed vertical rod exit devices at their
    factory. If you are installing a vertical rod device at a job site
    on existing doors, then use surface vertical rods.

    Concealed vertical rod exit devices are preferable because they are
    protected from damage by the door. However, it is an especially skilled
    installer who can install one in the field, and at that, it is a time
    consuming and difficult job.

    Mortise exit devices offer superior durability, and are otherwise
    the best choice when retro-fitting an exit device to an existing door
    that already has a mortise lock.

    Exit Device Trim

    The exit device goes on the inside, or interior side of the door,
    and exit device trim goes on the outside. Exit device trim is available
    in different functions. Below are the most common functions:

    • Key locks and unlocks lever handle or thumbpiece. Trim can be
      left unlocked for periods of time allowing free entry.
    • Key retracts latch. Exit device is always locked from outside,
      entry by key only. Not available on some vertical rod exit devices.
    • Key unlocks trim only while key is inserted. User turns key, operates
      control for entry. Trim is relocked when user removes key.
    • Passage function: trim is always unlocked allowing free entry.
    • Dummy trim: trim is rigid, usable as a handle to pull the door
      open when either the bar is dogged down using the dogging feature
      (see above) or when the latch is retracted or the device released
      by other means.

    Exit Device Options

    Exit devices are available with a wide variety of options that increase
    their functionality. These include:

    • Alarm
    • Touchpad or latchbolt monitoring switches
    • Electric latch retraction
    • Electric dogging
    • Delayed egress