T775P SERIES 2000 ELECTRONIC STAND-ALONE CONTROLLER
62-0256—11 4
Temperature Sensor Wiring
Electrical Shock Hazard.
Can short equipment circuitry.
Make sure that metal tube of sensor does not
short against T terminals in wall-mounted case.
IMPORTANT
Poor wiring practices can cause erratic readings
from the sensor. Avoid the following to ensure
proper operation:
•Do not route the temperature sensor wiring with
building power wiring.
•Do not locate the temperature sensor wiring
next to control contactors.
•Do not locate the temperature sensor wiring
near electrical motors.
•Do not locate the temperature sensor wiring
near welding equipment.
•Make sure good mechanical connections are
made to both the sensor and the controller.
•Do not mount the sensor with the lead wire end
pointing up in an area where condensation
can occur.
If any of the above conditions cannot be avoided,
use shielded cable.
NOTE: Each temperature sensor must be wired to a
single T775 controller. However, a benefit of
the T775 controller’s accuracy is that there is
no more than a 2°F differential between any
two T775 controllers.
Reset Temperature Control
If you are implementing two-sensor reset control, Sensor
A or C must always be the controlled temperature and
Sensor B must always be the controlling temperature.
For example, in a reset control based on outside
temperature, Sensor A or C must be the inside sensor
(supply, boiler, chiller, or return) and Sensor B must be the
outside sensor.
Multiple Parallel Sensors
Multiple sensors can be parallel-series wired to sense
average temperatures in large spaces. To maintain control
accuracy, the number of sensors to be parallel-series
wired must be of the n
2
power (for example, 4, 9, 16, etc.).
See Fig. 3.
Fig. 3. Parallel-series wiring of sensors.
Temperature Sensor Wire Type and Size
Temperature sensors use standard AWG 18/2 unshielded
wire. For cable runs greater than 25 feet or where
electrical interference may be a problem, shielded cable is
recommended. See Fig. 4.
Refer to “Temperature Sensor Calibration” on page 8 for
wire size selection where cable runs are longer than 25
feet.
Fig. 4. Sensor Wiring — Showing shielded cable connection to Sensor A.
TO T775 CONNECTIONS (SENSOR A) OR (SENSOR B).
SENSORS
M24380
M24374
SHIELDED
CABLE
SHIELDED
CABLE
NOTE: TO MINIMIZE NOISE PICKUP,
MAKE CONNECTION FROM
SHIELDED CABLE AS CLOSE AS
POSSIBLE TO SENSOR BODY.
SENSOR
T
T
T
T
SENSOR A
SENSOR B
SENSORS A, B, AND C USE THE TWO TT CONNECTIONS AND
ARE POLARITY INSENSITIVE.
1
1
T
T
SENSOR C
NOTE: SHIELDED CABLE MUST BE
CONNECTED TO AN EARTH
GROUND.
HOWEVER, DO NOT GROUND
SHIELDED CABLE AT SENSOR END.
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