Viessmann Vitocrossal 300 CA3 2.5 Installation And Service Instructions Manual page 32

Installation
Electrical Connections
Legend
A Minimum pressure limiter
B Maximum pressure limiter
C Further safety equipment
Note: Periphery equipment attached to the aBÖ plug must
be operated on a normally closed circuit.
32
(continued)
* *
Vitocrossal 300 CA3 Series 2.5 to 6.0 Installation/Service
Connecting External Safety Equipment
Connection at plug aBÖ.
Note: 'Live' contacts lead to short circuits or phase failure.
The external connection must be potential-free.
1. Remove jumper from terminals 17(L) and 18(L), 19(L)
and 20(L) or 21(L) and 22(L).
2. Make connection of the safety equipment to 17(L) and
18(L), 19(L) and 20(L) or 21(L) and 22(L).
*Factory Installed high limit temperature switches
(refer to page 107 for additional information).