There is often confusion between the terms ‘Door Entry System’ and ‘Access Control System’. This is in part because Access Control Systems often include audio or video door entry as a feature and many systems sold as door entry systems can actually include simple elements of access control.
In reality a basic Door Entry System provides a method by which a person - usually a staff member or building resident - who is usually already inside the building - is able to talk with visitors and remotely open a door to allow entry to the visitor without the effort of having to go to the door to operate it manually (as you would with a doorbell).
To achieve this a door panel is fitted at the entrance, which connects to a handset or monitor unit which is called from the door panel via a button press or button press sequence.
The units are fitted with speakers and microphones, plus (for Video Door Entry) a camera and monitor screen so that the operator can tell who entry is being given to. This type of system is fundamentally used to provide convenience, plus a small amount of security. The security of the door is reliant on the locks fitted to it, any door closing mechanism and on the users of the door. Tailgating is a common problem with such systems.
With lower specification door entry systems the opening of the door from outside the property by the staff member or resident would usually have been done using a traditional lock and key and would not have involved any electronic controls.
When an electronic system of unlocking is used, for example by adding an electronic keypad or proximity reader outside the building, and the property owner gaining entry using a PIN or proximity token, then some aspects of access control are now included.
In many cases a standalone door entry system might be integrated with an Access Control System from another manufacturer to secure a door. Usually this is because the access control system is being used in other areas of the building, or the system provides features that cannot otherwise be supplied via the door entry system. Where this is the case, it usually means that the access control system is directly in charge of the door and locking mechanisms, and the door entry system requests door opening via the access control system.
Care should be taken that wiring which controls locks for a door entry system are protected and located on the secure side of the door, to prevent access through vandalism. This should be worked out at the design stage, since some door entry designs have lock wiring located inside the external door panel. Systems are produced to differing criteria, and as such are manufactured to different levels of quality and security. With these systems, a knowledge of the available range of products is very useful. In some specialist door entry applications, door panels can call telephone extension numbers within the building or call telephone numbers of call handling centres or remote individuals for 24/7 or vetted access to a building.
So what does a modern audio door entry system consist of? For the purposes of this exercise we will start with a simple single door – single handset kit.
Typically (but not always), these would be installed along with, or integrated as part of an Access Control System, which would facilitate staff or resident access to the premises and deal with locks, break glass units, exit buttons, etc. Door Entry systems in the UK should be manufactured to meet BS EN 50486.
Here are the basic system components:
1) The Power Supply Unit (PSU): The power supply unit on some systems might supply differing voltages for door panels, handsets and locks and also it might double up as the controller for the lock. In higher specification systems, the power supply, locking, door panel and handset junction terminations are handled by a central control box. Typical examples of this are available from several manufacturers and are seen in many local authority buildings.
2) Cable: There are specific cables which are required by each manufacturer for the circuits from their system’s components. These can include intruder alarm cable, CW1308 telephone cable, Cat 5e, Cat 6, flexible mains cables, Belden 8723, etc. Each manufacturer's requirements are slightly different, though the considerations of audio or data line type, voltage, current, resistance, and volt-drop remain the same.
3) Door Panel: The door panel is the visitor’s interface with the system. Usually fitted at selected entrances, these units provide the means to call the correct handset and in some instances, also provide a ‘Trade’ or ‘Service’ button to allow free access for deliveries and maintenance within a specified time period. In some of the more affordable systems, the door panel is the central hub from which all wiring radiates, however this layout allows for the possibility of system tampering, which may be a consideration.
4) Handset: Usually fitted in a flat’s hallway or near a reception desk, these units allow staff or residents the means to communicate with the visitor and remotely control the door lock. Some models have monitor screens for viewing pictures from cameras mounted either in the door panel or nearby.
5) Magnetic lock or Strike lock : This is the main form of security fitted to the actual door frame and door. The lock may optionally be controlled via an access control system. It keeps the door locked until the lock release button is pressed on the handset or until the press to exit button, green break glass unit or fire alarm interface is triggered.
6) 'Press to Exit' Button : Also known as PTE, Press to exit, request to exit, or REX, This button is fitted on the inside (secure side) of the door, and is used to allow people to exit from the building by disengaging the lock for a pre-set time period. Due to COVID-19, proximity (no touch) PTE buttons have become popular.
7) Green 'Break Glass' Unit : This is supplied in the form of a purpose designed, manually operated switch that can disengage the lock in the event of an emergency, bypassing any timer mechanism that might otherwise re-engage the lock again. Used mainly in conjunction with 'fail safe' lock types, such as maglocks.
8) Mains powered 'unswitched fused spur' outlet: Powered form a dedicated 230 volt ac supply, the unswitched fused spur unit provides the final means of fusing before the mains cable enters the control unit.
9) Fire Alarm System Link : This is not a requirement for every door or system, but where a proper Fire Alarm System is installed in the building, the Door Entry System (or at least the secured door's locks) should be considered for interfacing with the fire alarm to allow free means of egress in the event of a fire activation. Exactly which doors require fire alarm interfaces will be agreed as part of the building's fire strategy protocols.
In the economy ranges of Door entry systems, there are differing wiring topologies according to type and manufacturer.
For instance, a typical Videx door entry kit would have the door panel forming the central hub of the wiring configuration. On the handset, connection 1 and 2 are the directional speech lines, 3 is a –ve supply, 4 is the ‘buzz line’ and 5 is the door release switched –ve. Additional handsets with separate button calling are therefore a simple bolt-on option.
Whereas a typical BPT Door Entry intercom system would have the power supply forming the central hub of the wiring configuration.
System Wiring.
On a fully-wired door entry system like the one we are looking at, the cable forms the backbone links between all of the devices 'in the field' and the main cable hub point. The cable you use for each circuit should conform to the system manufacturer's specifications. You should always use the correct cable for the job - never skimp and use cheaper cables, as faults and erratic operation may very easily result.
Installing System Cables
Care should be taken when installing the access control system cables that they are kept away from mains cabling - In order to comply with BS 7671, all cables of ""Voltage Band I"" (SELV 0-50 volts rated) should be segregated from cables of ""Voltage Band II"" (low voltage / mains rated) This carries on down to which holes you bring the cables into the control panels and power supplies. Mains cabling should not enter any panel or PSU alongside door circuit cabling.
Generally, all cables should also be protected from risk of damage. This means that cables running down walls should ideally be contained inside the wall void, or protected either by capping (if being plastered over) or conduit or be fitted inside mini-trunking or similar. In areas where there is little traffic (like attic spaces and under-floor voids) it is okay to run in cabling without additional protection, as long as it is securely clipped to the building fabric. Don't leave hammocks of un-clipped cable hanging in the attic or under the floor, as this causes stress on the cable.
Magnetic lock or Strike Lock
The magnetic lock or strike lock part of any door entry install tends to be the most precise and labour-intensive area of the installation. For those with reasonable joinery skills and taking a bit of care, strike locks can be fitted quite quickly, though the finished article is rarely pleasing to the eye. Magnetic door locks tend to be bulky items that present their own issues, though 'slimline' and flush units can be used in certain situations. Of course, there are several other door or frame mounted locking options that are available, albeit for considerably more money.
Magnetic Lock
Magnetic locks are a staple item in the typical access control system, but with cheaper door entry kits they are less in favour due to their higher power requirements over those of a strike lock. In this case separate power supplies are fitted and the maglock is controlled via a relay. Higher spec systems can handle maglocks without issue. Several options of both mag lock and bracketry are available to help overcome most obstacles.
A basic mag lock works like this: The 'lock' unit, where all the wires connect to, is fitted on the door frame, normally on the top (transom) of the frame, nearest the opening edge of the door. The lock (if not flush) should also be fitted on the 'secure' side of the door so that it can't be tampered with. A thick metal plate, called an 'armature plate' is fitted on the door, and aligns with the lock to form a strong electromagnetic bond when the door is closed, and the lock energised.
The armature plate itself is securely, but not rigidly fixed to the door. Usually, the plate is held in the centre by a countersunk bolt, and stopped from spinning around on the bolt by a few split-pins which are fitted on the back of the plate at either end. These pins locate into similar sized, shallow holes which are drilled in the door face. At the centre-bolt between the door and the plate is fitted a couple of metal washers and a rubber one. When fixed correctly, the rubber washer allows the armature plate to move slightly to take up any difference in the angle between the door and the lock as it closes.
The lock itself should be fitted on the door frame only after taking into account the space needed between the lock and the door to allow the armature plate and washers to fit, with the door fully and properly closed. It is quite common to see doors where this calculation has been botched. The lock itself must be extremely well fixed to the frame, since they can cause serious injury if they become detached from the frame in normal service.
These locks are available in several voltages and ratings. The most commonly used ones are 12 volts dc units which usually cannot be powered directly from the door entry system. In this case, a separate 12v dc power supply would be switched via a relay to operate the maglock. Normally, these units are set for 'fail safe' operation (door unlocked when power is removed), and normal building exit is via a push to exit button. At minimum, a green 'break glass' unit should be fitted in-line with the lock, to cut off the power to the lock in an emergency.
Strike Lock
Strike locks are probably the cheapest locking units available for door entry systems, and due to the design of the cheaper door entry kits, are the lock of choice (see drawings above). These units fit on the door frame and align with a door 'keeper' or latch lock. When the door is closed, the keeper is engaged with the strike and rests within the strike's 'L' shaped release plate area. When the strike is activated, the solenoid within the unit unlocks the release plate, which can then move to allow the door keeper freedom to move away from the strike, thus unlocking the door. After the pre-set unlock time period, the solenoid will lock the release plate, and the door keeper will slide over it as the door closes and re-engage within the release plate area. These units are especially useful in low traffic or light duty applications. They are supplied for various AC and DC voltages, in 'Fail Safe' and 'Fail Secure' varieties.
The lock types above are the most commonly used types, although as we've said, many other options exist.
Fail Safe / Fail Secure
So what does Fail Safe and Fail Secure mean?
‘Fail safe’ locks would normally be energised when locked and de-energised when unlocked. With fail safe locks a power failure event would leave the secured door unlocked, allowing free access. There are many applications where fail safe locking is preferred, e.g. internal secured doors.
‘Fail Secure’ locks would normally be de-energised when locked and energised when unlocked. With fail secure locks a power failure event would keep the secured door locked. There are many applications where fail secure locking is preferred.
The circuit diagrams above for the two door entry kits both specify 12 volts AC fail secure strike locks, although both can be adapted to work with fail safe units.
'Press to Exit' Button
As we've mentioned already, this button has a different name depending on the manufacturer, but it's purpose is identical - it signals the system to allow exit from the secured area. On the really cheap kits or on poorly executed installs, this button is sometimes connected so that it directly applies or removes the power to the lock. This crude arrangement does work, but for the customer, leaving the building becomes a two-handed operation, since they would need to press the button and simultaneously open the door, else it would immediately re-lock. Generic buttons usually provide one 'normally open' switch pair, and one 'normally closed' switch pair, to cover all eventualities. In the case of the drawings above, no provision is made for the use of PTE buttons. In this instance a timed relay could be added to the circuit to allow the button to operate the lock for a pre-set time period.
Green 'Break Glass' Unit
The green - coloured 'Break glass' unit is a common addition to many system installs. These units are coloured green to differentiate them from the fire system ones, and are also labelled differently. These units simply provide a mechanical means of switching off (or on) the power to the lock in an emergency situation. For this reason they are usually wired into the lock circuit in such a way as they can make one or both power wires to the lock become disengaged (Fail Safe operation) or powered (Fail Secure operation). If a Fire Alarm System is installed, access doors (at the very least on the fire exit routes, but usually all doors) should be interfaced with them so that the fire system can unlock the doors in the event of a fire activation.
Relays
A relay is essentially an electrically operated switch. Typical relays that we would install use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays.
Relays are used where it is necessary to control a circuit by a separate low-power signal, where several circuits must be controlled by one signal, or where the controlling equipment and the controlled equipment must remain electrically separate.
The first relays were used in long distance telegraph circuits as amplifiers: they repeated the signal coming in from one circuit whose voltage had diminished due to volt drop over the length of cable and re-transmitted it on another circuit, with fresh voltage supplied from the relay station’s power source. Relays were used extensively in telephone exchanges and early computers to perform logical operations.
In the Fire and Security industry, we typically use relays to integrate otherwise incompatible systems together (e.g. a 12volt ac lock supply from a cheap door entry kit to the PTE input on an access control unit), or incorporate third party equipment.
Typical plug-in relay with DIN rail mounting connection base
Relays can be purchased as momentary, latching or timed types. The number of switches (poles) that are available within the relay unit can vary from one to six. The switches (poles) within a relay all ‘change state’ at the same time.
A relay switch ‘changes state’ when the electromagnet coil is energised or de-energised by the control circuit. For this reason the switches are usually supplied with three contact terminals. These are usually labelled:
C – Switch ‘common’ connection
N/O or NO – Switch ‘normally open’ connection (open circuit when the control coil is de-energised)
N/C or NC – Switch ‘normally closed’ connection (closed circuit when the control coil is de-energised)
‘Changing state’ involves the changeover of the N/O and N/C settings - normally open to closed and normally closed to open.
It is worthwhile to know in advance before specifying a relay for a task the following information:
Coil voltage: the voltage of the control circuit and if the voltage is AC or DC.
Switched voltage: the voltage of the relay controlled circuit
Switched current: the maximum current draw through the relay switch contacts.
Momentary, timed or latching operation
Number of switches (poles) required and type:
Single throw (N/O OR N/C terminals) or double throw (N/O AND N/C terminals).
Common system faults
No speech in one or both directions : This could be due to a faulty handset, faulty door panel speech unit, broken wire cores, or power issues.
No buzz on phone: Faulty button or cabling, handset damaged or off hook.
Locking issues : This could be due to a badly adjusted lock, power issues, faulty locks, or damaged wires.
Locks : These can be the source of 'back electromotive force' (back EMF) which can damage equipment. A correctly rated diode should always be fitted across the supply terminals of the lock. Some locks have these fitted as standard, or supply them as part of the fitting kit.
Door Faults : Joinery issues like twisted doors, loose hinges, broken handles, and failing or badly adjusted door closers, and other issues like vandalism can and do cause call outs.