RX for REX:

Aug. 1, 2007

REX is an abbreviation used in access control for devices and circuits involved in providing request to exit functionality.

REX devices customarily are pushbuttons, exit bars or motion sensors. REX functions can also be implemented using upgrade kits designed for these applications, or by performing site specific applications engineering.

Frequently, locksmiths installing access control systems will be supplied with terminal points for the connection of REX or remote door release devices. How the internal circuitry is designed to operate may vary. It is the system designer/locksmith installer's responsibility to understand the features and operation sequence of the equipment, and to ensure that the configuration of the REX and the locking device provides the required life safety.

Typically a REX device will produce contact activations as a consequence of someone attempting to egress through a door. These contacts are then used to signal and switch various system operations.

REX devices are used for three primary reasons. First, access control systems may control doors which are also being monitored for security management, to indicate exception conditions on remote monitoring equipment.

“Forced Door” conditions occur when the controlled door is opened without a valid card to gain entry or without a REX to egress. “Propped Door” or “Door Ajar” conditions occur when the controlled door remains open, unlocked or ajar for longer than the system is programmed to allow.

Second, access control systems may utilize electrically actuated bolts, electromagnetic lock, shear locks, or a combination of locking devices which do not provide an integral means of manually unlocking the door to allow free egress.

For the majority of applications, building and Fire Codes will mandate that any door along the path of egress (and most internal doors) allow free egress at all times.

There are exceptions, but these exceptions generally apply to institutional applications (such as detention facilities or psychiatric wards), government high security and special locking arrangements (such as delayed egress).

Suitability of an opening for anything other than Free Egress will always be ultimately determined by the AHJ (Authority Having Jurisdiction). There may be times when more than one AHJ may be involved, in which case conflicts between them have been known to occur, as each may interpret the code differently.

The bottom line is that for those situations where the electric locking device does not have any integral means of unlocking it for free egress, the REX components are critical elements in the system design.

An example would be where an access control panel is used to control a door equipped with an electromagnetic lock. Although connecting a normally open momentary switch to the REX terminals on the access controller could be expected to trigger the door output on the access controller to unlock the electromagnetic lock for the pre-programmed unlock time, this is not considered a safe installation.

Most approved REX devices are available with two sets of output contacts, and when configuring access controls for doors using electromagnetic locks, the second set of contacts should be wired in series between the door output and the locking device. In this way, as long as the button is depressed, the electromagnet is unlocked, even if the access controller output fails to release the lock. A failure in the access controller, a failure in the REX switch, or a broken wire could all prevent the REX button from triggering the access controller.

All possible failure modes should be carefully considered, and countermeasures designed into each system you install. As a security professional, you should always strive to achieve the safest system possible, rather than one that passes the AHJ's inspection, or meets the client's budget.

In most jurisdictions, electromagnetic locks are only permitted in buildings equipped with fire alarms or sprinkler system that can produce a signal to the locking systems to instantly cut power to the electromagnetic locks. The wording of such codes may be misleading, because frequently electromagnetic locking systems will be augmented with backup batteries so that if the building experiences a power outage, the electromagnetic locks will remain locked. In these situations, if the fire alarm interrupts the line voltage to the lock power supplies, the intent of the code will not be realized. Therefore the power supplies you use with electromagnetic locks should ideally have a factory installed provision for interfacing with the fire alarm system, and the fire alarm contractor should complete the wiring connections between the fire alarm and the locking system. A functional test should be performed and documented.

An alternative would be to supply an approved relay into the electromagnetic lock circuit, and have the fire alarm contractor connect the FACP (Fire Alarm Control Panel).

It is also good practice to utilize more than one REX device on an opening, in the interests of end-user safety and convenience, since there are many emergency situations where the fire alarm will not be triggered or a REX device may be rendered inoperable.

Suppose the code calls for a means of egress that requires only a single movement, and does not require any previous knowledge of how to achieve egress. So going back to our example of the door with the electromagnetic lock and the pushbutton, an experienced access control installer may also use additional auxiliary REX devices and enhancements to make it easier for individuals to achieve egress in an emergency.

One leading manufacturer offers a component REX system comprised of a specially designed REX motion sensor and a pushbutton REX switch with an integral electronic timer. The system is designed so that if the REX motion sensor fails to unlock the door (for example due to smoke obscuration), the pushbutton will unlock the electromagnetic lock by interrupting power to it. Both the motion sensor and the pushbutton are wired to the access controller and the a second set of contacts in both the motion sensor and the pushbutton are wired in series with each other the power circuit to the electromagnetic lock. This setup is particularly well suited for inswinging doors (that is on doors which open towards the end-user trying to egress).

REX motion sensors are specially designed to release locks on doors for individuals egressing, and to actuate doors and gates equipped with door operators. They have the specially configured contact arrangements and internal timers required for deployment on access control doors. A big problem with earlier technology REX motion sensors was that they were too sensitive and their field of view was hard to setup. These are not typically considered problems for motion sensors used for security, where a high capture ratio and large volumetric protection are desirable features.

REX motion sensors can be precisely tuned to the opening, thereby preventing false triggering by passersby, who are not intending to egress, and sensing individuals who may approach the doors quickly, or others who might hesitate or walk slowly when transgressing the door. REX motion sensors can also be obtained with direction sensitivity, so that they will only trigger on movement in one direction. It is important that the REX sensor not trigger extraneously, because when triggered, the subject door is unlocked and therefore a security breach.

Another solution is the pneumatic pushbutton switch. This type of device does not require power to provide the timed door unlock function that an electronic timer module or access controller would provide. When the button the pneumatic switch is pressed, an air valve controls how long the contacts will remain actuated. This type of switch can be ordered with dual contacts.

Typically REX devices are supplied with D.P.D.T (Double Pole, Double Throw) contacts, with switch contact ratings adequate to be connected into the actual electric locks power circuit. Carefully evaluate the power requirements of your locking devices to properly specify a switch contact rated for the load and duty cycle of your installation.

Illuminated REX devices are also valuable in ensuring safe egress when normal structure lighting might be out, and people need help to be directed to the door and locate the REX switch. Every emergency exit has an illuminated or luminescent EXIT sign; it only makes sense that the REX also be illuminated.

The final REX DEVICE Category is the exit bar, and it is perhaps the most desirable device for use on out swinging doors. I consider the exit bar as the primary REX device, and then add additional equipment to the extent required.

Exit bars are electronic, mechanical, or a combination of two technologies. Electronic bars use sensors to detect pressure or someone touching them to release the locking device and signal the access control system. Mechanical bars use switches and the pressure of the person attempting to egress to actuate the bar.

Dual technology exit bars use two technologies to increase their reliability. Illuminated and luminescent models are available.

The single biggest advantage of the exit bar is that it is a universally recognizable means of unlocking a door, and a person approaching a door on foot, will intuitively push on the bar, even if he or she does not know what the word EXIT means.

The single biggest drawback to the exit bar is that it is necessary to get the required wiring from the exit device to the hinge edge of the door, then from the hinge edge of the door over to the fixed door frame. Because the door moves, whatever method used to transfer the circuits are exposed to stress, movement and possibly vandalism. Electric hinges, pocket transfers, door loops are the most commonly deployed transfer solutions with other specialty products also available to professional designers with special requirements.

REX kits are also available for many exit devices, where signals are required for interfacing with security systems, or supplemental locks are being retrofitted to existing structures to ramp up building security.