3-9
IM 253421-01E
Before Starting Measurements
3
3.7
Wiring the Measurement Circuit when Using
External PT/CT
WARNING
When using an external CT, do not allow the secondary side of the CT to go
open-circuit while power is supplied, otherwise an extremely high voltage will be
generated on the secondary side of the CT.
CAUTION
A load current flows in the thick lines shown in the diagrams; therefore, a wire
with sufficient current capacity must be used for these lines.
Use of a PT (or CT) enables measurement of voltage or current even if the maximum
voltage or maximum current of the object to be measured exceeds the maximum
measuring range.
• If the maximum voltage of the object to be measured exceeds 600 V, connect an
external potential transformer (PT), and connect the secondary side of the PT to the
voltage input terminals.
• If the maximum current of the object to be measured exceeds 20 A, connect an
external current transformer (CT), and connect the secondary side of the CT to the
current input terminals.
Wiring diagram when using the PT and CT
SOURCE
LOAD
L CT
PT
V
v
SOURCE
LOAD
L CT
PT
V
v
l
l
A
V
±
±
A
V
±
Input terminal
Input terminal
±
Note
•
Using the scaling function enables direct reading of measured values on the display. Refer to
section 4.5, “Setting the Scaling Constant when External PT/CT is Used.”
•
It must be noted that measured values are affected by the frequency and phase
characteristics of PT and CT.