Document Number: MAN0045
Issue: 4.01
Page
14
of
16
LOCK DEVICE BACK E.M.F SUPPRESSION
It is important to check that the locking device is suppressed. Any electromagnetic device will produce a back
E.M.F when power is removed. This can interfere with and even damage other electronic equipment. Most
good locking devices will already have suppression fitted. If not, you should fit an appropriate suppression
device across the coil.
In the case of solenoid operated locks, a flywheel diode will do. Connect the cathode (Bar End) to the positive
and the anode to the negative terminal of the coil. The diode will need to be rated at the full operating current
of the coil.
Do not use a diode for a mag-lock, as this will cause an excessive delay to the release of the door. A MOV or
VDR is a far better choice. Polarity is not critical, but make sure the rated voltage is greater than the normal
operating voltage of the lock.
