Application Note AN-003
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Electronic Solutions, Inc.
This application note describes a common problem that technicians encounter in the field when installing the ES530 multifunction module, along with the solution.
Noise from Magnetic Locks & Strikes
Without protection, breaking the circuit of a 24V magnetic lock or electric strike can easily create a spike of a thousand volts or more! Such spikes wreak havoc with all microprocessor controlled equipment. Consequently, to prevent failures such as lock-ups and other random glitches you must provide varistor (MOV) protection across the relay contacts of any circuit being used to switch magnetic locks or strikes! We include one MOV for each locking device that we are switching via our interlock (either automatic doors that are unlocked when idle, or manual doors). Proper operation is not guaranteed without the use of these devices.
It has been our experience that connecting the MOV across the switching device (relay contacts) provides better overall protection from transients than connecting it directly across the offending device (lock or strike).