50 GC250 Technical Manual
EAAM057608EN
5.11
The current measurement shall be made exclusively by means of current transformers (CTs)
with secondary by 5Aac and which guarantee suitable isolation.
WARNING!
Do not connect to terminals T.38..T.41 for measuring conductors
currents with mains voltage
.
Any current measurement needs a power of about 1VA; however, CTs of 5VA are
recommended, to compensate for leaks along the connection cables.
The maximum current that the device can measure directly is of 5.3Ac, beyond which the
measurement circuit gets saturated. The controller board is still able to measure (but with
gradually decreasing precision) down to about 20 Ac
solely for transient situations and for a
time lower than 3s ,,
such as measuring over currents or short circuit currents on
the system, using an algorithm to compensate for the saturation of the
measurement circuits.
The TA measuring the three currents have a sole terminal
T.41
for the return current.
The measurement is carried out by shunt.
WARNING!
IMPORTANT: terminal T.41 with all CT’s back, MUST be connected
to T.01 GND supply negative of the device.
If the CTs have to be connected to other devices in addition to the controller, it must be the
last in the series.
Connect to terminal
T.38
a terminal of the CT connected on phase L1.
Connect to terminal
T.39
a terminal of the CT connected on phase L2.
Connect to terminal
T.40
a terminal of the CT connected on phase L3.
Connect to terminal
T.41
the returns of all three CTs.
For single phase connection, terminals
T.39
and
T.40
should not be connected.
