Controlling Access With Interlocks and Mantraps

Special door control features may be required for some access control projects. The markets or geographic area you serve will have a lot to do with your activities with respect to these special projects.



Lockdown systems permit the immediate disabling of request-to-enter devices (card readers, keypads) into a defined area. Schools and universities are implementing lockdowns in order to protect students and teachers in the event of violent behaviors.

The lockdown may also involve securing the premises against egress, such as in a detention or institutional setting. Lockdown systems can be triggered from a central location, and usually it is desirable that in the lockdown can be initiated from within the protected area.

In military, government detention and healthcare facilities, control of entry and egress may be allowable, while the usual life safety rules may be suspended.

In a crisis situation, it may be required to immediately take control of all movements in or out of a facility.



Sequencers (wireless and wired) are not emergency devices but may be used for convenience and environmental purposes. For example, both low and full energy automatic door operators used in vestibules may incorporate sequencers so passage through the vestibule may be accomplished with minimum effort for the end-user.

Sequencing the doors also helps to contain environmental air, to reduce heating and cooling costs, as well as enhancing the comfort of the building occupants.



Locking or non-locking interlocks can be used in a number of situations for a variety of reasons and may involve multiple openings.

The basic operation of a two-door locking interlock is that when one of the doors is open, the other cannot be opened. Non-locking interlocks can inhibit the operation of handicapped actuators, card readers or other request-to-enter devices if a door is not closed.

When individuals are entering or leaving secured areas, an interlock may be used to enforce the proper usage of access controls so movements can be documented and controlled to prevent piggybacking or passback.

Piggybacking and tailgating occur when an unauthorized person achieves access by following and authorized person through an access point.

Passback refers to the uncontrolled, consecutive unauthorized passage through an access point. Anti-Passback prevents misuse of a security door control system by establishing a specific sequence which must be followed in order for the system to grant access and in some applications egress. For every use of a card to enter, there be a corresponding use to egress before the card can be used to enter again. The Anti-Passback rule can be applied to a single access control point or globally to all access points within a system.



In clean room environments, it may be required that the perimeter around an area be secure at all times, so an interlock will be used to create an air lock between doors. This arrangement of doors and controls are also referred to as mantraps. Mantraps may be employed where hazardous substances are being moved.

Marshals are using mantraps in order to maintain law and order at entrances to Federal Courts and buildings. In detention and institutional situations, there may be a requirement to maintain external control over prisoner or patient movement, where an interlock system will allow safe and controlled movements.

In certain settings, there will be shared facilities such as bathrooms between adjoining spaces. Interlocks can be used to afford the desired convenience and privacy to users.

Research laboratories may wish to prevent the possibility of the unintentional entry or escape of radio frequencies. Specially designed radiation-proof enclosures and doors may also incorporate interlocks so the RF seal is maintained.

Interestingly, unlike delayed egress and similar special locking arrangements, interlocks which may have a negative impact on the life safety characteristics of an opening are not clearly referenced by Life Safety and Building Codes. Be careful to obtain approval from the authorities having jurisdiction (AHJ) for your installation and be aware that there may very possibly be more than one AHJ involved.

Door control systems should be easy for management to control and end-users to understand and navigate. The door control system should also be safe. The use of visual lock status indicators will help management and users know the locked status of every door. As individuals negotiate the labyrinth you’ve created, Red and Green go-no-go lights will help them transgress area with minimum frustration and confusion.

Remote controls and emergency overrides will allow immediate intervention should the situation require.

Since your system will be controlling movement in both directions, an interface with the premises fire alarm may be required, and provisions for interfacing should be included in your design and specification.


Dortronics 4300

The Dortronics 4300 Series 2-Door interlock features two powered relay outputs for direct connection to locks and traffic lights, if used. It may be easily configured during installation for locked, unlocked or locked-unlocked operation by means of jumpers. An optional remote connection provides for override of one or both door locks by remote console, panic switch or similar actuator.

The standard 4300 series controller comes mounted in a NEMA enclosure. The standard configuration includes a 12 or 24 VDC (user selectable) 4 Amp power supply with fire alarm interface. A signal from an external fire alarm (normally closed dry contact) will cause the power supply fire alarm relay (FAR) interface relay to de-energize, cutting low voltage power to all door locks, LEDs, sounders and the PLC. The power supply manual shipped with the system has additional details.

  • Power connections are made at the factory.
  • Door switch contacts must be closed when the door is secure. Twisted pair wiring – AWG gauge 22 or larger is recommended.
  • Door unlock time is determined by an external device, typically a card reader, motion sensor, pushbutton or remote console. Only normally open dry contacts should be used. Do not apply voltage to a 4300 input.
  • Maglocks and strikes are connected to the powered outputs directly. Both powered outputs are fused. LED indicators to indicate lock status may be wired in parallel.
  • LED and incandescent indicator lights, typically red to show a locked or inaccessible condition and green to show an unlocked or freely accessible condition, may be connected

The 4300 controller offers an optional lock override function. If this function is required, it must be specified when the controller is ordered. Remote lock override terminals may be connected to a set of dry contacts. On closure, the associated door lock relay will energize, unlocking the door bypassing the interlock function. To release both doors by a single set of contacts, wire the Remote inputs in parallel. This is separate and in addition to the FAR on the power supply that kills power to the locks and controller in the event of a fire alarm condition.

Building codes vary by location. The installer is responsible for understanding and working in compliance with all local codes and regulations as defined by the governing authority.


Dortronics 4700

The 4700 series Programmable Logic Controller is an economic way to control up to four interlocked doors. The controller logic sequences simultaneous requests for access and monitors unsecured doors to maintain the highest level of security at all times.

The Dortronics 4700 is suitable for air locks or security mantraps, with up to four normally unlocked doors or three normally locked doors. The controller may also be customized to control automatic door openers and provide timing and logic sequences for biological wash-down controls. Typical configurations provide outputs for traffic lights, forced doors and an emergency panic release input.

It is compatible with any access control system. The request for access input recognizes any normally open dry contact.

The 4700 series PLC controller is paired with a heavy duty 4-amp power supply that includes a Fire Alarm connection for emergency egress and provides power to operate the maglocks and electric strikes and traffic lights. An alarm output is also provided.

Typical Configurations:

  • #47211-U – Standard 2-Door / 1-Room Normally Unlocked
  • #47211-L – 2-Door / 1-Room Normally Locked
  • #47321-LU/S – 3-Door / 2-Room1-Normally Locked & 2-Normally Unlocked with 1-Shared Door
  • #47431-U/2S – 4-Door / 3-Room Normally Unlocked with 2-Shared Doors


Dortronics 4900

The 4900 series door interlock controller can provide power and control for up to 128 doors. The PLC logic allows only one door, in any defined area, to be unsecured at a time. Simultaneous requests for access or requests for access while another door is unsecured are denied to maintain the highest level of control.

Suitable for air locks or security mantraps, this door interlock system will effectively control normally unlocked doors, normally locked doors or any combination of both. The controller may also be customized to control automatic door openers and provide timing and logic sequences for biological wash-down and air purging controls.

Fail-safe or Fail-secure Locks: Lock control relays with DPDT outputs allow use of 12 or 24 volt DC fail-safe maglocks and fail-secure electric strikes. Both types can be used simultaneously on the same doors.

Access Control Compatible: Any access control system can be used with the 4900 series controllers. The request for access input recognizes any normally open dry contact.

Optional 12/24 VDC Lock Power: While the PLC controller requires regulated 12 or 24 VDC input, the integral 4204 power supply also provides ample 12 or 24 VDC output to operate maglocks and/or strikes for each of the doors. The heavy duty power supply is ready for hook-up to the fire alarm system. An alarm output is also provided for monitoring the control system.

Traffic Control Indicators: The DPDT relay outputs can be used to control lighted door status indicators, providing visual feedback as to when a door may be accessed. For user convenience, a green light typically signifies that a door is ready for access and a red light indicates that a door is un-accessible. Dortronics #7201xL2-H hi-intensity LEDs are ideal for use with this system.

Typical configurations are:

  • #4900-PLC - Programmable controller capable of interfacing with up to sixteen I/O modules for a total capacity of 128-Inputs and 128-Outputs
  • #4900-I/O Module - Eight digital Optically isolated inputs accept dry contact signals from door status switches and request-for-access devices such as push buttons or card access
  • systems. Four DPDT relay outputs provide control for maglocks, strikes, traffic lights or other low voltage devices.
  • The #4900-I/O module has additional capability providing digital outputs which may be utilized for up to four more relays controlled by the PLC



  • Enclosure- 12” x 16” x 4” deep
  • NEMA enclosure will accommodate PLC controller & one I/O module with power supply. Additional modules require larger enclosures.
  • PLC Module - 6-1/8” x 3-3/8” overall
  • I/O Module - 10’ x 3” overall
  • Electrical - AC Input - Fused 110 VAC
  • DC Output - 4 amp field selectable 12 or 24 VDC
  • Inputs - Door Status (Dry contact closed when is door secure)
  • Request for Access (Dry contact normally open)
  • Relay Outputs - DPDT Contacts rated 3 Amps @ 28 VDC for each door (Magnetic lock or strike & LED traffic indicators for each door. One common on each relay is fused.

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