Hioki ST5540, Instruction Manual, Page: 16 / 326

1.3 What is Leakage Current?
10
High voltage is present in an electrical appliance that uses a commercial power supply as its main power
source. Touching such equipment may expose a person to an electrical shock when current passes
through the body to ground. This electrical shock is the result of "leakage current" or "touch current." Nor-
mally, electrical equipment is grounded to protect against electrical shocks. Current regularly flows
through the grounding wire, but should an abnormality (due to faulty design or fault) occur in equipment,
the resulting electrical shock may cause serious personal injury and sometimes lead to the death of the
victim. For this reason, leakage current measurements including single-fault conditions
*1
are strictly regu-
lated.
Leakage current measurements performed according to the applicable standard makes it possible to ver-
ify the safety of equipment.
*1
What is a single-fault condition ?
This refers to when equipment has a fault in a safety protection measure, or a fault that may result in a
hazardous condition.
Leakage current testing includes the following three
single-fault conditions .
1. Disconnected grounding wire (not applicable in current tests of leakage current)
2. One wire in the power cord is disconnected (neutral power supply wire)
3. External equipment damage
*2
(patient leakage current II and patient leakage current III)
*2
In JIS T0601-1:1999 classified as a single-fault condition.
Not a single-fault condition , the instrument is capable of switching polarity during measurements and
retaining a recording of the phase with the highest leakage current.
1.3 What is Leakage Current?