Woodward MRM4, Manual, Page: 38 / 460

Installation and Connection
Slot X3: Current Transformer Measuring Inputs
Rear side of the device (Slots)
This slot contains the current transformer measuring inputs.
Current Measuring Inputs and Ground Current Measuring Input
The device is provided with 4 current measuring inputs: three for measuring the phase currents and one for
measuring of the earth current. Each of the current measuring inputs has a measuring input for 1 A and 5 A.
The input for earth current measuring either can be connected to a cable-type current transformer or
alternatively it is possible to connect the summation current path of the phase current transformer to this input
(Holmgreen connection).
Current transformers have to be earthed on their secondary side.
Interrupting the secondary circuits of current transformers causes
hazardous voltages.
The secondary side of the current transformers have to be short circuited
before the current circuit to the device is opened.
The current measuring inputs may exclusively be connected to current
measuring transformers (with galvanic separation).
•
Do not interchange the inputs (1 A/5 A)
•
Make sure the transformation ratios and the power of the CTs are
correctly rated. If the rating of the CTs is not right (overrated), then
the normal operational conditions may not be recognized. The
pickup value of the measuring unit amounts approx. 3% of the rated
current of the device. Also the CTs need a current greater than
Page 38 EN MRM4 01/11
X1
X2 X3
Slot1 Slot2 Slot3
X100 X
10
1
X103