2-11
IM WT310E-02EN
Making Preparations for Measurements
2
2.5 Precautions When Wiring the Circuit under
Measurement
To prevent electric shock and damage to the instrument, follow the warnings below.
WARNING
• Ground the instrument before connecting measurement cables. The power cord to use is a
three-prong type power cord. Insert the power cord into a grounded three-prong outlet.
• Turn the circuit under measurement off before connecting and disconnecting cables to it.
Connecting or removing measurement cables while the power is on is dangerous.
• Do not wire a current circuit to the voltage input terminal or a voltage circuit to the current
input terminal.
• Strip the insulation covers of measurement cables so that when they are wired to the input
terminals, the conductive parts (bare wires) do not protrude from the terminals. Also, make
sure to fasten the input terminal screws securely so that cables do not come loose.
• When connecting measurement cables to the voltage input terminals, only connect
measurement cables that have safety terminals that cover their conductive parts. Using
a terminal with bare conductive parts (such as a banana plug) can be dangerous if the
terminal comes loose.
• When connecting cables to the external current sensor input terminals, only connect cables
that have safety terminals that cover their conductive parts. Using a connector with bare
conductive parts can be dangerous if the voltage is 42 V or higher.
• When you apply current directly to the current input terminals to measure it, the voltage
of the item under measurement appears at the external current sensor input terminal. To
prevent electric shock, remove the cable connected to the external current sensor.
• When the voltage of the circuit under measurement is being applied to the current input
terminals, do not touch the external current sensor input terminals. Doing so is dangerous
because the terminals are electrically connected inside the instrument.
• When connecting a measurement cable from an external current sensor to an external
current sensor input terminal, remove the cables connected to the current input terminals.
Also, when the voltage of the circuit under measurement is being applied to the external
current sensor input terminals, do not touch the current input terminals. Doing so is
dangerous because the terminals are electrically connected inside the instrument.
• When using an external voltage transformer (VT) or current transformer (CT), make sure
that it has enough dielectric strength for the voltage (U) being measured (2U + 1000 V
recommended). Also, make sure that the secondary side of the CT does not become an
open circuit while the power is being applied. If this happens, high voltage will appear at
the secondary side of the CT, making it extremely dangerous.
• When using an external current sensor, make sure to use a sensor that comes in a case.
The conductive parts and case should be insulated, and the sensor should have enough
dielectric strength for the voltage of the circuit under measurement. Using a bare sensor is
dangerous, because there is a high probability that you might accidentally touch it.
• When using a shunt-type current sensor as an external current sensor, turn off the circuit
under measurement before you connect the sensor. Connecting or removing the sensor
while the power is on is dangerous.
• When using a clamp-type current sensor as an external current sensor, make sure that
you understand the voltage of the circuit under measurement and the specifications and
handling of the clamp-type sensor, and then confirm that there are no dangers, such as
shock hazards.
• For safety reasons, when using the instrument after mounting it on a rack, furnish a switch
for turning off the circuit under measurement from the front side of the rack.
• For safety reasons, after you connect the measurement cables, use the included screws to
attach the current input protection cover (screw tightening torque: 0.6 N•m). Make sure that
the conductive parts do not protrude from the protection cover.
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