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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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