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Current is the current that flows from any enclosure part through a person back to ground if it
were contacted by a person. The Applied Part Leakage Current or Patient Lead Leakage
Current is any leakage that flows from an applied part, between applied parts or into an
applied part. The Applied Part Leakage Current test is required only for medical equipment.
All of these tests are used to determine if products can be safely operated or handled without
posing a shock hazard to the user.
Touch Current Testers provide the capability of meeting the Touch Current test specified in
the following standards; UL 544, IEC 950, UL 1950, IEC 601-1, UL 2601, UL 1563, UL 3101,
IEC 1010 and others. The Touch Current test, is a test which measures the leakage current
of a product, through a circuit that is designed to simulate the impedance of the human body.
The simulation circuit is called the Measuring Device (MD). The instrument has five
different MD circuits, selectable through the menu, which are representative circuits designed
to simulate the impedance of the human body under different conditions. The impedance of
the human body will vary depending upon point of contact, the surface area of the contact
and the path the current flows. For these reasons, the specifications of the Measuring
Devices are different depending upon the type of test being performed as well as the maximum
allowable leakage current. Leakage current measurements are performed on products under
normal conditions and single fault conditions as well as reversed polarity. This simulates
possible problems, which could occur if the product under test is faulted or misused while the
product is operating under high line conditions (110% of the highest input voltage rating of the
product).
Touch Current tests are normally specified as “Type Tests” or “Design Tests” which are
performed during the development of the product. This helps verify that the design is safe
but it does not guarantee the safety of the products being produced on the production line.
The only way to be sure you are shipping safe products is to test each product at the end of the
production line. The user may perform a Leakage Current test along with other common
safety test such as Dielectric Withstand, Insulation Resistance, and Ground Bond on the
production line with a single connection to the device under test.