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Rev. A.2, 10/03 Page-6
reduce the switching life of the relay. The arc also creates electronic noise which could cause
the microprocessor to malfunction. The MOV should be spliced into the lock power wires as
close to the lock as possible. Some DC electric locks have internal kickback protection
including all Securitron Magnalocks. You don’t need the MOV for these locks but if you are
not sure, it does no harm to install the MOV so long as the lock power is in the 12-24 volt range.
FIG. 4: DC LOCK - AC POWER WIRING
NC1 C1 NO1
AC IN F DC IN /OUT
+
TRANSFORMER
12 OR 24 VAC
DC FAIL SECURE
OR FAIL SAFE LOCK
MOV
IF FAIL SECURE
IF FAIL SAFE
NOTE: MOV NOT REQUIRED IF
SECURITRON MAGNALOCK IS USED
+
3.3.3 DC LOCK WITH DC POWER
Select a power supply of the same voltage as the lock (12 or 24). Make sure the capacity of the
supply is large enough to operate both the DK-26 and the lock. The DK-26 does not require
regulated power but certain specialized electric locks do, so follow the rule of matching the
power supply to the requirements of the lock.
DC locks come in “fail secure” and “fail safe” versions. A fail secure lock is secure when not
powered and a fail safe lock is secure when powered. All magnetic locks are fail safe. Figure 5
shows correct wiring. The positive DC terminal connects to the common of relay #1 and either
the NO1 terminal (if the lock is fail secure) or the NC1 terminal (if the lock is fail safe) connects
to the lock’s positive power input. This is shown in dotted lines. You only connect one of these
two terminals. Note that some DC locks are polarized and you must be sure to connect the lock
power wires correctly to positive and negative. Others are not polarized and it doesn’t matter
which way they are connected. Consult the lock instructions.
Note installation of the MOV across the power wires to the lock. The MOV is the small black
disk shaped component furnished loose with the DK-26. Its function is to absorb inductive
kickback from the lock’s coil. Without the MOV, this kickback voltage will arc over the relay
contacts and reduce the switching life of the relay. The arc also creates electronic noise which
could occasionally cause the microprocessor to malfunction. The MOV should be spliced into
the lock power wires as close to the lock as possible. Some DC electric locks have internal
kickback protection including all Securitron Magnalocks. You need not employ the MOV for
these locks but if you are not sure, it never does any harm to install the MOV so long as the lock
power is in the 12-24 volt range.