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Rev. A.1, 8/01 Page- 8
UnLatches, the extra current capability will always be there as each unit will operate at different
times so each can draw extra current from the power supply when needed.
If you are using a smaller capacity power source, you may be satisfied with the operation of
the Mortise UnLatch since the reduction in torque is only noticeable when the door is pre-
loaded. There is, however, an important electronic effect. During the brief moment while the
motor is starting to move, the Mortise UnLatch will “try” to draw 4 or 2 Amps (depending on the
voltage). A power supply of lower capacity will react to this condition by sharply dropping its
voltage for the same period. While this will not harm the power supply, it may “crash”
microprocessor equipped devices like digital keypads (such as Securitron’s model DK-11 or DK-
26) that are being operated from the same power supply. If, therefore, your installation
includes a digital keypad, or other microprocessor equipped device, make sure you have full
power supply capacity (or a smaller supply with battery backup) or use a separate power supply
for the keypad or other device.
4.2 WIRE GAUGE SIZING
If the power supply is some distance from the lock, voltage will be lost (dropped) in the
connecting wires so that the Mortise UnLatch will not receive full voltage. The amount of
voltage that is dropped in the wires depends on the resistance of the “round trip” wire run
compared to the resistance of the Mortise UnLatch. The issue is complicated by the fact that
the resistance of the Mortise UnLatch is 20 Ohms @ 12 VDC or 80 Ohms @ 24 VDC when it is
operating (the motor is moving) but the resistance drops as low as 3 Ohms @ 12 VDC or 12
Ohms @ 24 VDC for 100 milliseconds just as the motor starts. If the unit is denied full voltage
during this motor start period, it will operate but with less torque so it will not release the latch as
crisply when the latch has pre-load on it. Selecting thick wires to power the Mortise
UnLatch will maintain strong torque even during start up. The following table shows
distances from the Mortise UnLatch to the power source and calls out the wire gauge needed to
fully maintain torque. Note that if your installation requires the power source to be more distant
or has other complications, the factory can assist you.
Distance (one way) 50 ft. (15 M) 100 ft. (30 M) 200 ft. (60 M)
Wire Gauge for UNL-12 16 14 12
Wire Gauge for UNL-24 22 20 18
4.3 LATCH STATUS SENSING
The Mortise UnLatch includes a latch status sensing feature. When
the door is closed and the door latch has engaged the Mortise UnLatch
(specifically the springlatch plunger has been pushed in by the door
latch), the Mortise UnLatch will report this secure condition by
outputting a closed circuit condition between the white (COM) and
green wires (see the drawing to the right). When the door is not
securely latched, the closure will be between the white and blue wires. This dry SPDT output
can carry 1 Amp @ 30 VDC maximum. This signal is normally connected to the building alarm
system and it provides superior information compared to conventional door contacts which show
only that the door is closed, not whether it is latched. Note that the Mortise UnLatch’s ability to
report on the latched status of the door depends on it receiving constant power. Any time
power is cut to the Mortise UnLatch, it will report the door as secure regardless of whether it is
latched or not.
The Mortise UnLatch uses the information as to whether the door is latched or not for a second
purpose. The Mortise UnLatch will not operate unless the latch is in the secure position
(the springlatch plunger is pushed in). Operationally, the door can be opened anyway (it is not
latched) so there is no benefit to the end user from the Mortise UnLatch operating unless the
door is latched. Inhibiting operation when the door is not properly closed and latched also helps
protect the Mortise UnLatch against operating its motor into some jam condition in the event of
severe misalignment of the door.
NC
NO
COM
WHITE
GREEN
BLUE