By David Miller M.I.S. (SA)
Generally speaking, the majority of locks that are operated only by keys are mechanical - and use no power at all. They are not affected by load shedding - but this is not always the case.
Locks used in access control are often mechanical locks, which will stay locked in the absence of power, but paired with an electric striker the can be released electrically.
If they are electric-locks – they usually use 12 volt (or sometimes 24 volt) power to unlock them. They usually remain LOCKED in the absence of power.
Weather rim mounted (visible on the surface of the door) or mortise mounted (concealed inside the door) these locks require power only to unlock them. In the case of disconnection of power they usually remain locked – but cannot be opened electronically (i.e. via remotes, intercoms, card, tag, pin or biometric readers) unless there is enough battery power available for this purpose.
Magnetic locks are all electro- magnets – they UNLOCK if power is disconnected – whether due to power failure, battery failure, electronic failures or wires being cut - they cant tell the difference. A magnetic lock can only re-lock when both of the following take place:
· power to the mag-lock is restored; and
· the door or gate is fully closed again.
Mag locks draw power 24/7 just to stay locked, regardless of whether the door is being used or not. Most magnetic locks draw between 0.25 and 0.5 of an amp, 12 or 24 volts, round the clock, and are the most likely of all locks to unlock during load shedding, particularly where there are several periods of load shedding in a day, and batteries do not have enough time to recover. The trend in the industry of using the smallest batteries and small capacity chargers to satisfy customer demand for lower prices does not help the situation. Given the current frequency of load shedding, the capacity of batteries used for these locks needs to be at least doubled or tripled depending on the size of the existing batteries and the load being drained by the mag lock, and by the other accessories that are draining the batteries constantly, day and night.
Mechanical locks with electric strike-releases (electric strikers)
in most cases in South Africa, mechanical locks are paired with 12 Volt electric strikers of the FAIL-SECURE type - which means that in the event of disconnection of power, they remain locked (and should be able to be opened by a key-bypass if fitted). These strikers draw no power, except for a few seconds at a time when the door is being released - hence they are usually able to be operated normally during load shedding, provided they have a battery backup system in good working order.
In some buildings FAIL-SAFE strikers are used - which means they are designed to unlock for life- safety reasons, in the event of disconnection of power. Fail-safe strikers are usually connected to a building- wide fire detection system, which will unlock all of the fail-safe strikers in the building when a fire is detected, to allow free escape. These fail-safe strikers are power-hungry much like the magnetic locks described above and require power 24/7 - just to stay locked.
ALL access control equipment will usually have some constant current-drain – including tag, face, finger, PIN and card readers, intercoms, and any device that has a lit display or indicator lights.
Motorised gates, motorised garage doors, electric fences and burglar alarms all use batteries – which may not be able to cope with the current long power-outages. Batteries may need to be replaced more frequently or up sized where possible. DON’T wait for the battery to fail before replacing it!
Batteries and battery chargers
Motorised gates, burglar alarms, access-control systems, electric locks and magnetic locks used in Souh Africa are generally fitted with either lead-acid or gel type atteries. In recent times, lithium batteries are being sold to power inverters and such equipment. Note that lithium batteries require a different type of charger and will not become fully charged if used with most of the chargers in common use.
The above is a guide of a general nature, and does not obviate the need for expert, site-specific advice.