9 - 32 VM600 MPS hardware manual (standard version) MAMPS-HW/E
Edition 17 - February 2018
Configuring the four local relays on the IOC4T
CONFIGURATION OF MPC4 / IOC4T CARDS
Normally de-energised (NDE) and normally energised (NE) refer to the relay coil state (that
is, the relay switching circuit) when the hardware is powered and the signal driving the relay’s
control circuit is in a normal (non-alarm) state.
• For relays configured as normally de-energised (NDE), the control input to the relay’s coil
is off by default so there is a closed circuit between the NC and COM contacts (and an
open circuit between the NO and COM contacts) for a normal state.
• For relays configured as normally energised (NE), the control input to the relay’s coil is
on by default so there is an open circuit between the NC and COM contacts (and a closed
circuit between the NO and COM contacts) for a normal state.
NOTE: An advantage of normally energised (NE) relays is that the “de-energise to trip
principle” allows problems with hardware to be detected (for example, due to
power supply or wiring failures).
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