Continuous current is a term used in relation to locking devices. There are a few key concepts that it’s important to understand before we get to continuous current.
Fail safe and fail secure
Fail safe and fail secure are key terms in the world of locking. Knowing the difference (and where to install each type) is essential.
What does fail safe mean?
Fail safe locks are unlocked when power is removed. Power is applied in order to lock the door and prevent access. This type of lock is all about safety. They are used to ensure that people inside a building or area can get out safely in the event of an emergency. If something happened that caused a power failure, the lock would automatically unlock to allow people to exit.
Fail safe locks are generally used on emergency exits and external doors. They are not recommended for doors that protect equipment or assets that would be made vulnerable if the door was left unlocked in a power cut.
What does fail secure mean?
Fail secure locks are locked when power is removed. Power is applied in order to unlock the door and allow egress or access. These locks are all about security. In the event of an emergency power failure or temporary power cut, the door would remain closed and locked.
Fail secure locks are used to keep assets or equipment secure and protected from intruders during outages of electrical power. As a result, they are not recommended for emergency exit doors.
Coils inside locks
Inside electric strikes, there are coils. The coils act as relays within the lock to trigger the locking or unlocking action of the strike. The larger the coil, the longer it can sustain continuous operation.
Fail safe locks require a constant supply of power to keep them locked the majority of the time. When someone needs to open the door, the power is temporarily removed until they are through the door. Power is then applied again to re-lock the door. This means that fail safe locks require a much larger coil inside them than fail secure locks.
Fail secure locks are locked as standard. Power is only applied for short bursts of time in order to release the lock and allow access. When the door closes again after access, power is removed and the door locks. This means that the coils in standard fail secure locks don’t need to be as large as those in fail secure locks. This also means that standard fail secure locks tend to be less expensive than standard fail safe locks.
Continuous current fail secure locks
If a fail secure lock is listed as having continuous current (often abbreviated to CC) or being continuous rated, it means that the coil inside it is the same size as the equivalent standard fail safe lock. Its capacity for taking current over long periods of time is therefore much greater than a standard fail secure lock.
If a standard fail secure lock had power applied to unlock it for long periods of time, it would overwhelm the coil. The coil would burn out and the lock would be permanently damaged. In a continuous rated lock, the larger coil can cope with being powered continuously for much longer periods.
Where would continuous current locks be used?
Think about the main front door of a small office building. If there is a power cut, it’s likely you’ll want that door to remain locked in order to keep the building secure and stop people from entering without authorisation. Therefore, a fail secure lock is best suited to this environment.
However, what if the door needs to be kept unlocked from 8:30am to 6:00pm so that the office workers can get in and out quickly and easily? If a standard fail secure strike was fitted and set to stay unlocked all through the working day, its coil would burn out. The lock would be rendered useless.
In this case, a continuous current fail secure lock will be the best solution. Outside of working hours, a power failure would leave the door robustly locked. During working hours, people can freely come and go without obstacle, and the lock’s coil won’t be damaged.