EXTERNAL CONNECTIONS
External connections are connected on terminal blocks
X28, X29 and X30 on the PCB (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 sensor (BT1) is placed in the shade on a
wall facing north or north-west, so it is unaffected e.g.
by the morning sun.
The outdoor sensor is connected to terminal block AA2-
X28:14 and to any input on terminal block AA2-X29.
If a conduit is used it must be sealed to prevent condens-
ation in the sensor capsule.
13
1211
109 14
BT1
BT1
BT50
GND
BT25
AUX9
AUX8
AUX7
AA2-X28
AA2-X29
Temperature sensor, external flow line
Connect temperature sensor, external supply line (BT25)
to terminal block AA2-X28:12 and to any input on termin-
al block AA2-X29.
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
temperature in the display on S1255.
Fit the room sensor in a neutral position where a set
temperature 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 tem-
perature, 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. The room
sensor is connected on terminal block X28:13 and to
any input on terminal block AA2-X29.
If a room sensor is to be used to change the room
temperature in °C and/or to fine-tune the room temper-
ature, the sensor must be activated in menu 1.3 "Room
sensor settings".
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
combination with underfloor heating will not
give a noticeable difference in room temperat-
ure.
External energy meter
One or two energy meters (BE6, BE7) are connected to
AA2-X28:1-2 or AA2-X30:7-8.
21Chapter 5 | Electrical connectionsNIBE S1255
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