Leakage current

Leakage current is the current that flows from the unit through the grounding conductor into a household ground. Leakage current could shock an individual if the household grounding is not sufficient or there is an intentional or unintentional interruption of grounding connection.

Leakage current of 3 milliamps through the heart would create a mild shock and some pain ; 8 milliamps would cause an interruption in heart function (cardiac arrhythmia) which could eventually kill a healthy person in seconds.

Note: the requirement for medical equipment however is more stringent; a fatal shock could result if the patient is in a weak or unconscious condition.

CLASS I EQUIPMENT
: Equipment where protection against electric shock is achieved with the combination of basic insulation and protective earth ground connect to case.

CLASS II EQUIPMENT: Due to the fact that there is no protective earth ground in the equipment, the protection against electric shock relies on double insulation or reinforced insulation.

CLASS III EQUIPMENT: Equipment in which protection relies upon supply source from SELV circuits and in which hazardous voltages are not generated.

PATIENT AUXILIARY CURRENT: Current flowing in the patient in normal use between parts of the applied part and not intended to produce a physiological effect; for example, bias current of an amplifier or current used in impedance plethysmography.

PATIENT LEAKAGE CURRENT: Current flowing from the applied part via the patient to the ground or flowing from the patient via an F-type applied partially to the ground, originating for the unintended appearance of a voltage from an external source on the patient.

Requirement
For Information Technology Equipment (I.T.E.)

Classification - Maximum Leakage Current
Class I - 0.75mA (Hand held equipment) & 3.5mA (All others)
Class II - 0.25mA

For Medical Equipment

Current - Normal Condition - Single Fault Condition
Earth Leakage Current - 0.5mA - 1mA

Other than the medical leakage current requirement mentioned above, there are other leakage current requirements in IEC 601-1(Medical), such as patient leakage current, patient auxiliary current and enclosure leakage current. (We will not discuss these topics as they do not apply to our power supplies.)

For Class 2 Equipment

Type of Equipment - Maximum Leakage Current
Portable Unit - 0.5mA
Stationary Unit - 0.75mA

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