Hioki ST5540, Instruction Manual, Page: 40 / 326

3.2 Connecting the Power Cord
34
Description of isolation transformer
The standard requires that an isolation transformer is used for performing leakage current measure-
ments.
Should the equipment under test break down during measurements, unforeseen current could be gener-
ated resulting in tripping the earth leakage breaker. Such an event could shut down other electrical equip-
ment used in the same facility, which could cause a serious accident. Since an isolation transformer
isolates equipment under test from the earth leakage breaker, equipment breakdown will not have an
impact on the earth leakage breaker or on any other equipment.
• Use of network B1 or B2 requires the connection of an isolation transformer
capable of outputting a voltage equivalent to 110% of the rated power supply
voltage of the equipment under test.
• When network C is selected, an isolation transformer is required.
However, when the power on polarity switching function is not used, connect
the neutral wire on the secondary side to ground. When the function is used,
not to connect the neutral wire to ground.
• The [LINE IN] and [AC IN] power supplies are isolated from each other.
• Use the cable supplied with the ST5540 and ST5541 instruments to connect
the equipment under test [LINE IN]. Do not connect any other electrical appli-
ance to this inlet.
• The [LINE IN] terminal cannot be used to connect a single-phase three-wire
or center-grounded power supply (for example, a stabilized power supply).
• Nor will the input of 110% of a rated 250 V power supply voltage be a prob-
lem.
Voltage fluctuations of ±10% from the rated supply voltage are taken into
account. Nor will the input of 110% of a rated 250 V power supply voltage be a
problem.