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MT Series SSC81U Electronic Valve Actuator, 24 Vac Floating Control
Operation
Mounting and
Installation
Wiring
Siemens Industry, Inc.
A 24 Vac control signal to terminal Y1 extends the actuator shaft proportionately to the
length of time the signal is applied.
A 24 Vac control signal to terminal Y2 retracts the actuator shaft proportionately to the
length of time the signal is applied.
In the event of a power failure with no control voltage, the non-spring return SSC81U
will hold its last position.
CAUTION:
A valve must be connected to the actuator before applying power.
If applying power to the actuator when a valve is not connected, the
actuator will respond to a control signal and the shaft will extend until it
reaches its maximum end stop. Thereafter, it will not respond to any
signal. If this occurs:
1. Disconnect power.
2. Turn the manual position indicator (See Figure 4 and Figure 5) on
the top of the actuator to the 0 position and verify the actuator
shaft completely retracts.
3. Connect a valve to the actuator, reapply power. The actuator will
return to normal operation.
Mount the actuator in one of the allowable positions shown in Figure 1.
When mounting the actuator in a plenum, the proper cable must be attached to meet
local codes. Allow 8 inches (200 mm) above the actuator and 8 inches (200 mm) behind
the cable for service.
Use earth ground isolating, step-down Class 2 transformers. Do not use
autotransformers.
Determine supply transformer rating by summing total VA of all actuators used. The
maximum rating for a Class 2 step-down transformer is 100 VA.
Do not power more than 10 actuators by one transformer. (Use a 0.5-amp fuse on
secondary actuator.)
NOTE:
Can be wired either neutral or hot switched.
CAUTION:
Terminals must be properly wired for correct function and full life of the
actuator.
Figure 1. Mounting Position.
Technical Instructions
Document Number 155-314P25
June 1, 2023
Page 3
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