Apply Surge Suppression Devices to Maglocks and Electric Strikes

Posted by Dan DeMerchant on

Don't forget to install the surge suppression devices, especially if they are included with the lock when installing electric strikes and maglocks. Many people doing installs make this common omission that causes technical support calls and premature equipment failure. They think that these devices are optional.

Diodes, MOVs, or TransZorbs (TVS) act as surge suppressors that prevent high voltage spikes from radiating to other electrical components. A strike is an inductive load (coil of wire) internally, and when they are allowed to de-energize rapidly (when a controlling relay cuts power), the strike briefly acts as a source of voltage. This voltage can be much higher (>1000V) than the voltage that was originally supplied to energize the strike (12V or 24V). The higher voltage is generated by a rapidly collapsing electric field in the solenoid of the strike.

You want to clamp this voltage (keep it at a low level <40V). Unclamped, this brief high-voltage spike can radiate to the access control and other low-voltage systems, causing electrical malfunctions and damage. These spikes cause large arcs that can very quickly destroy contacts of relay outputs and even vaporize processors and other sensitive components found in electronic door control hardware.

Varistors are not polarity sensitive, but diodes are, so note the details in your strike installation manual. When installing diodes as suppressors, the side with the line marked on the device is the cathode--that side that goes on the positive voltage input of the power supply at the strike or maglock. The anode goes on the negative (the side without the line). Also, resistors are not diodes!

Change these devices out after a few years. Reference standard BHMA A156.31 for specifications in this area when installing access control systems.


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