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4. ELECTRICAL WIRING
When using SX75 controllers to directly drive VMD electric actuators
damage to the controllers internal relays might occur due to switching the
relatively heavy electrical loads.
Auxiliary relays should therefore always be installed between the controller
and the valve drive actuator. This will protect the controller from switching
the actuators high current loads, avoid introducing high current loops within
the proximity of the controller, and provide an easily replaceable switching
element outside of the controller.
This advice is in line with that recommended by other manufacturers of
similar equipment and is considered to be good working practice.
6 Auxiliary Relays for Valve Motor Drive actuators
VMD signal
to actuator
VMD signal
from SX75
controller
Neutral
Relay 2
Relay 1
Live
Neutral
Y1
Y1