THE HUMBLE STRIKE
The humble electric strike has been a major player in the electronic locking hardware field for many years and, with correct specification in the right application, it remains one of the mainstays of electronic locking today.
Applications can be found in all areas of life from single door to large PC-based systems covering multiple doors and sites.
All strikes basically work on the principle of electronically controlling the temporary free movement of the jaw (striker) allowing for door opening without manual retraction of the latchbolt.
Dependant on model (mortice or rim mount) electric strikes work in conjunction with the majority of popular mortice or rim night latches. Ideally, the latch should have a dead-locking facility whereby the latch bolt cannot be forced back into its case because of the action of the snib resting against the electric strike forend. This facility offers extra protection when a strike is fitted to an outward opening door.
WHICH STRIKE SHOULD BE USED?
This depends on a number of factors. What level of security is needed? What type of door material is the strike to be fitted to? Single or double door? Is monitoring of the strike required? What power supply unit is to be used in the system? Is the system AC or DC? What else is running off the PSU?
LEVEL OF SECURITY
There are three basic categories.
TYPE OF DOOR
Door material - internal or external, single or double doors.
Electric strikes can only be used on single action inward OR outward opening doors. For double action swing-through doors other locking solutions like solenoid bolts, magnetic shear locks or double action electric latches are available. Nowadays there are strikes suitable for nearly all door styles and materials, the most popular being timber and aluminium followed by steel, and occasionally, uPVC.
Potentially, uPVC causes the most problems because of the narrow and often complicated section containing steel re-enforcing. Another problem is the fitting of a suitable lockcase into the narrow uPVC framing to operate with the strike. If the door contains a multi-point lock it is likely to be impossible to fit an electric strike.
If the door contains, or can be fitted with a latch, the best option could be to fit a narrow style sashlock and operate with a sashlock strike either in a UK or DIN faceplate format.
Whilst a sashlock can improve the level of security in any door when the deadlock is thrown, care should be taken to ensure that the bolt is removed prior to attempting the operation of the strike.
The first quantity usage of strikes was in the United States in aluminium doors and frames. This in turn led to an ANSI (American National Standards Institute) specification being produced. The ANSI short faceplate strike (flat or radius faceplate for single or double doors) became the standard for aluminium, whilst a further development was the introduction of a longer faceplated variant which made the ANSI style strike suitable for use in timber door applications.
With the introduction of centre-hung aluminium doors in a 4 inch (101.4mm) framing section, the need became apparent for lead in or extension lips to allow the latch free entry into the jaw of the strike without interference from the frame. Originally a mix and match of the long and short faceplate variants covered steel doors, whilst products designed specifically for timber and steel doors offering longer shallower and narrower bodies are now available.
Watch out for door gaps. The most commonly sold strikes in the UK operate successfully with no more than 1/8 inch (3mm) gap between the frame and door leaf.
Depending on model, most manufacturers produce strikes with or without a monitoring facility. This function relays back the state of the strike via single point monitoring of the latch in the jaw of the strike or by dual monitoring of both the latch and solenoid operation. For door state monitoring, consideration should be given to using a separate reed switch on the door/frame.
POWER TO LOCK/POWER TO OPEN
Fail Open (Power to Lock) or Fail Secure (Power to Open) are features of the electric strike that will be site dependant. For example, if the strikes are tied into the fire alarm system it is likely that they will be required to Fail Open (Fail Unlocked) once power to the strike is removed. Under other circumstances the strike may be required to fail in the locked position requiring the use of a Fail Secure (Power to Open) strike.
AC OR DC?
Where security is involved you cannot always expect a low cost AC strike to offer the same level of security that can be achieved by using a more expensive medium/high duty strike. Pick a product that is fit for the purpose. Short-term savings can work out very expensive. Most of the low cost door entry systems operate on AC rather than DC. Alternating Current produces the familiar buzzing sound which is not heard with DC systems, and AC strikes are only available as Fail Secure (Power to Open). More sophisticated systems operate on DC allowing for continuous silent Fail Open (Power to Lock) or Fail Secure (Power to Open) operation.
POWER SUPPLY UNITS
One of the most important areas for consideration when using any electric locking device is the PSU. Correct specification will help ensure fault-free running and ensures the PSU puts out the correct voltage required to run the electric strike within the tolerances stated. Remember to take into account any other products running off the same PSU. Most access control systems in the Australia run off 12v DC with the other common type being 24v DC.
Normally 24v DC runs at half the current draw of 12v DC which may be of assistance when working out what PSU to use. Most of the Australia fire alarm industry runs on 24v DC. If possible, ensure it is a regulated PSU whilst consideration should also be given to the gauge of wire used to supply the product. Long and thin wire runs could lead to voltage drop at the product and further problems.
These have included higher holding forces; rapid Power to Lock/Power to Open and vice versa changeover; more shallow overall depth reducing frame cut-outs and possible weakness; rebated face plates for timber doors; low current consumption; low heat generating solenoids; cast one-piece bodies; supplying templates to assist fitting; weather resistant models and extended warranties. Three companies now offer UL rating, with one offering both UL and CE approval.
An area of concern is fitting electric strikes to outward opening doors. Potentially doors fitted with standard ANSI strikes are left vulnerable because of the open lead-in extension lip, often unavoidable on aluminium door applications.
This led to the development of lipless and wrap-around strikes now available from a number of manufacturers which, when used in conjunction with an integral door or face fix T bar, offer the highest levels of security attainable with an electric strike.
Electric strikes are not the all-encompassing solution for all problems - like all things in life the right product still needs to be correctly specified and installed in the right place, and all reputable manufacturers will give guidance to help the installer make the right choice.