Viessmann Vitocal 300-G Installation And Service Instructions Manual page 81

Electrical connections
Plug sXS
Terminals Function
222.3 Switching external heat
222.4 source with two high limit
safety cut-outs (max. 70 °C)
to protect the heat pump and
to stop the secondary pump
(cont.)
Explanation
Zero volt contact
Note
■ The switching contact is a zero volt
N/O contact that is closed when a heat
demand is issued.
■ Never route low voltage via this con-
tact; that requires an on-site relay.
■ The boiler water temperature sensor in
the external heat source (plug F20)
must capture the average temperature
of the external heat source.
Connection values (contact loads):
■ Voltage: 230 V~
■ Max. switching current: 4(2) A
Connect the high limit safety cut-out on
site:
■ In series to the secondary pump (ter-
minal 211.2 on the main PCB).
■ In series to the switching of external
heat sources.
Installation sequence
81