Q&A: Electronics 101

We have to install a shear lock on a Herculite door with a rail at the top. The door swings both ways. After researching the available shear locks, I am wondering; since it is a Herculite door, what sense does it make to install a 2700 lb. lock, when the door will probably shatter under considerably...



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We have to install a shear lock on a Herculite door with a rail at the top. The door swings both ways. After researching the available shear locks, I am wondering; since it is a Herculite door, what sense does it make to install a 2700 lb. lock, when the door will probably shatter under considerably less pressure?

We all know that glass doors are not the epitome of security, but they are aesthetically pleasing, and a rather common architectural feature. Electrical locks are frequently used on this type of door because it is desirable to control access, or use a clock to automatically lock and unlock. The locking cylinder, which is typically in the bottom rail, is difficult for many individuals to reach, or they feel they are put into a compromised position while bending over to lock or unlock them.

Since your door is bi-swing, and you have a channel at the top, you probably will want to use a concealed shear lock with the armature mounted in the top of the door and the magnet in the header. Selecting a shear lock whose physical size will allow installing it is the first criteria.

I would recommend selecting the highest power/best designed shear lock you can budget into the job, because it will pay you back over time.

Bear in mind that the published rated holding force is somewhat optimistic: it assumes that full voltage is being applied to the shear lock, and all other conditions which might adversely affect the bond are ideal.

One condition which can adversely affect locking and bonding is the distance between the armature and the electromagnetic portion of the shear lock. Herculite doors are famous for dropping and shifting as the pivots, the door closer, and the building in which the door is installed begin to wear, weaken, and shift. These parameters will challenge the shear lock to be able to properly align and pull up the armature.

If you start off with a marginal shear lock, it’ll be a hummer; you are guaranteed to be returning to the job repeatedly to tweak the shear lock to maintain satisfactory operation.

For example; one shear lock manufacturer advises that its product be installed so that the armature and electromagnet actually make contact when the door swings past it to be sure the gap between the armature and the electromagnet are minimal, and therefore the shear lock has the best chance of locking. Need I elaborate?

Other manufacturers’ shear locks offer mounting kits which make adjustments to the armature height quick and easy, and whose holding and pulling power assure your system will operate with minimal hassles.

An architect made the statement at a job site meeting that state law REQUIRED that a licensed architect do the design for the job if there is an alteration to a building that alters “access.” Is this true?

I do not agree with the statement that an architect must design an access control system, although laws vary from state to state regarding the installation of low voltage, life safety and electronic security systems.

I think that the term ‘access’ in the context of whatever law he was citing means the physical location and dimensions of doors. That is to say, that once a structure is issued a Certificate of Occupancy, it is unlawful to alter the structure by removing or altering a door, since the characteristics, width, and numbers of doors in a building are based on its size, type of occupancy, and number of occupants.

Similarly, it is unlawful to add doors (without an architect’s participation) because adding a door might jeopardize the structural integrity of a wall or fire-stopping characteristics of the premises. Such alterations might also require rewiring or relocating pipes or ducts.

As far as installing door control and security systems, the golden rule is to never impede egress. If you are dealing with a fire-rated door system, be certain your work does not jeopardize the door’s rating.

In certain situations, provisions must be made to allow entry by emergency services such as firefighters. In other situations, doors must be able to meet pressure tests to protect emergency responders and also to mitigate the spread of fire and smoke.

Building Codes attempt to establish minimum acceptable requirements, but hardly define preferred or recommended practices.

A good way to begin any system design is by identifying the possible failure modes which might prevent the system from operating safely, or what system elements will best ensure its safe operation. While adherence to the Code is the basis for any system, it is still necessary for experienced applications engineering and professional installation to realize the intended results.

Also, I would never ask a manufacturer or distributor rep to determine a life safety or security requirement for an application. I would, however define my requirements and ask a rep if his product met those requirements.

For any given application, you can call ‘x’ number of reps at company ‘y’, and get ‘z’ different answers. Is that how to design a system? Call up five reps, total their responses, calculate the mean, and go with the resultant answer?

No. The locksmith should endeavor to render the highest level of security possible for his customers.

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