Viessmann Vitovalor PT2 E11T Installation And Service Instructions Manual page 23

Notes on connecting to the mains supply
Ensure adequate selectivity if the new RCD is installed
downstream of an existing circuit breaker. In order to
ensure complete selectivity of two residual current
devices connected in series, the fault current of
upstream RCD must be at least 3 times as high as
A
that of RCD used to protect the Vitovalor PT2.
F
Adjust the activation times of both RCDs connected in
series in such a way that the disconnection time of
RCD is less than the shortest disconnection time
F
for RCD . Both conditions ensure RCD
A
Vitovalor PT2 responds earlier than upstream RCD
(cont.)
for the
F
A
l in A
Fig. 14
Preparing for installation
Response characteristics of the residual cur-
rent devices
A
F
23