YOKOGAWA WT500 User Manual page 83

3.11 Wiring the Circuit That You Will Measure with a VT or CT
Wiring Example of a Single-Phase, Two-Wire System (1P2W) with a VT and CT
Wiring Example of a Single-Phase, Three-Wire System (1P3W) with a VT and CT
3-22
Note
• After you have finished wiring, you must select the wiring system. For details, see section 4.2,
"Selecting the Wiring System."
• The thick lines on the wiring diagrams are the sections where the current flows. Use wires
that are suitable for the current levels.
• Make sure that you have the polarities correct when you make connections. If the polarity
is reversed, the polarity of the measurement current will be reversed, and you will not be
able to make correct measurements. Be especially careful when connecting the clamp type
current sensor, because it is easy to reverse the connection.
• The scaling feature can be used to transform the input signal to data that corresponds to
direct measurements. For information about how to set up this feature, see section 4.6,
"Setting the Scaling Feature When Using a VT or CT."
• Note that the frequency and phase characteristics of the VT or CT affect the measured data.
• For safety reasons, the common terminals (+/–) of the secondary side of the VT and CT are
grounded in the wiring diagrams in this section. However, the necessity of grounding and
the grounding location (ground near the VT or CT or ground near the power meter) vary
depending on the object being measured.
• To measure the apparent power and power factor more accurately on an unbalanced three-
phase circuit, we recommend that you use a three-voltage, three-current method with a
three-phase, three-wire system (3P3W; 3V3A).
The following wiring examples are for connecting a CT. When connecting a clamp-type
current sensor that outputs current, substitute the CT with the clamp-type current sensor.
The assignment of elements to the input terminals in the figures below varies depending
on the number of installed input elements. For details, see "Number of Installed Input
Elements and Wiring Systems" in section 2.3, "Measurement Conditions."
SOURCE LOAD
L CT
l
U
±
I
±
Input terminal
SOURCE
N
L CT
l
U
±
I
±
Input terminal 1
SOURCE
VT
V L CT
v l
U
Input terminal
VT L CT
V
v l
Input terminal 2
LOAD
VT
V
v
±
I
±
LOAD
VT
V
v
U
±
I
±
IM 760201-01E