Installation and connection
15
TGH1410en/03.2012
Connection of an additional cascaded measuring current transformer
If the residual current range of 10 A is not sufficient, an additional measuring
current transformer can be cascaded. Connect the measuring current trans-
former as illustrated in the drawing below.
Example:
An additionally cascaded transformer on the load side has a transmission ratio
of X
1
= 100 (500 A / 5 A). That means, when the lowest value of 10 mA is set at
the RCM420, a current of 1 A can only just be detected on the primary side of
the transformer on the load side. In order to reduce the value that can be de-
tected to 100 mA, 10 turns of the supply cable has to be routed through the
transformer on the RCM side.
Hence, the correction factor to be set is
n
RCM
= X
1
:X
2
= 100:10 = 10.
The correction factor can be set via the SEt/n menu. Refer to page 30.
The correction factor is factory set to 1 and relates to normal operation with
one Bender measuring current transformer only (X = 600:1).
Load
BENDER
W..., WR..., WS...
X
1
(x A/10 A)
(x A/5 A)
(x A/1 A)
n
RCM
=
X
1
X
2
X
2
RCM420
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