EXTERNAL CONNECTIONS
Connect external connections on terminal blocks X28, X29
and X30 on the base board (AA2).
-X29
-X28
1 0-5V
2 +5V
3 AUX1
4 AUX2
5 AUX3
6 AUX4
7 AUX5
8 AUX6
9 AUX7
10 AUX8
11 AUX9
12 BT25
1
1
2
3
2
3
4
5
6
7
8
9
10
11
12
GND
+12V
B
A
OT+
OT−
0-5V
PWM0
PWM1
CPU
EXT COM
INT COM
ERROR
POWER
+5V
GND
BE1
BE2
BE3
K10
-X27
NO
O
NC
AUX-RELAY
13 BT50
14 BT1
-X30
Sensors
Outside sensor
The outdoor temperature sensor (BT1) is placed in the shade
on a wall facing north or north-west, so it is unaffected, for
example, by the morning sun.
Connect the outdoor temperature sensor to terminal block
AA2-X28:14 and AA2-X29:GND.
If a conduit is used it must be sealed to prevent condensa-
tion in the sensor capsule.
13
1211
109 14
BT1
BT1
BT50
GND
BT25
AUX9
AUX8
AUX7
AA2-X28
AA2-X29
External supply temperature sensor
If an external supply temperature sensor (BT25) needs to
be used, connect it to terminal block AA2-X28:12 and to
terminal block AA2-X29:GND.
1211109
BT25
GND
BT25
AUX9
AUX8
AUX7
AA2-X28
AA2-X29
Room sensor
S1255 is supplied with an enclosed room sensor (BT50) that
makes it possible to display and control the room temperat-
ure in the display on S1255.
Fit the room sensor in a neutral position where a set temper-
ature is required. A suitable location might be, for example,
on a free inner wall in a hall approx. 1.5 m above the floor. It
is important that the room sensor is not obstructed from
measuring the correct room temperature, for example by
being located in a recess, between shelves, behind a curtain,
above or close to a heat source, in a draught from an external
door or in direct sunlight. Closed radiator thermostats can
also cause problems.
S1255 operates without room sensor, but if you want to read
the home’s indoor temperature from the display on S1255,
the room sensor must be fitted. Connect the room sensor
to terminal block X28:13 and AA2-X29:GND.
If a room sensor is to be used to change the room temperat-
ure in °C and/or to fine-tune the room temperature, the
sensor must be activated in menu 1.3 - "Room sensor set-
tings".
If a room sensor is used in a room with underfloor heating,
it should only have an indicatory function, not control of the
room temperature.
13121110
BT50
GND
BT50
BT25
AUX9
AUX8
AA2-X28
AA2-X29
Caution
Changes of temperature in accommodation take
time. For example, short time periods in combina-
tion with underfloor heating will not give a notice-
able difference in room temperature.
Pulse energy meter
Up to two electricity meters or energy meters for heating
(BE6, BE7) can be connected to S1255 via terminal blocks
AA2-X28:1-2 and AA2-X30:7-8.
BE7
+OT
+OT
0-5V
+5V
GND
95 6 7 8
AA2-X28
+5V
+5V
0-5V
+5V
AUX 1
AUX 2
AUX 3
AA2-X30
51 2 3 4
BE6
21Chapter 5 | Electrical connectionsNIBE S1255
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