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Microshock

Microshock

About

In electronics, leakage current is the unintended loss of electrical current or electrons in devices or components (e.g. capacitor). According to NFPA 99 (2005 version), the medical defines "leakage current as any current, including capacitively coupled current, not intended to be applied to a patient, that is conveyed from exposed conductive parts of an appliance to ground or to other accessible parts of an appliance".

Also, adding an additional ground wire (a redundant ground) in parallel with the power cord safety ground is not considered a significant modification to a medical device.

Currently, this term has been replaced with "Touch Current"

Calculation

Leakage current can be determine through the use of clampmeter, safety analyzer, or ohmmeter. You can use Ohm's law (E=IR) to get this answer. First, disconnect power to the circuit, and measure the leakage path's resistance (This is usually the rated resistance of the insulating material...you will need a Megohmmeter to measure insulation resistance, as it will be MUCH higher than a standard ohmmeter can measure). Next, rework the formula to solve for current:I=E/R or simply: divide voltage (V) by resistance (R). Finally. you can also use an inductive current clamp as mentioned above. This clamp measures electrical current by measuring the electromagnetic field strength of the current flowing through the wire.

Measurements

Currently, we only perform current leakage measurements with the power on and off. Reverse polarity is no longer a valid requirement because the sudden reverse changes in polarity will cause some power supplies to fail. Additionally, current leakage is now only to be performed during acceptance testing of new equipment and during repairs when the chassis of the unit has been opened. Monthly testing is no longer a documented or valid performance requirement.

References


Links

Fluke Leakage current measurement basics

See also

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