Rigel Medical

Knowledge Base Question

Q. What are the different leakage methods available?

A.  

There are three main methods of measuring Leakage currents. These are:

1. Direct Leakage
2. Differential Leakage
3. Alternative Leakage

A forth technique, using a current clamp is not part of this document however, does provide a method of determining leakage currents on fixed wired equipment.

The Direct Leakage Method:

The Direct Leakage Method is identical to the method used in the IEC 60601-1 standard, measuring the true leakage through a body model (measuring device) to earth.

Benefits

• Measures the true leakage on operational devices
• Means of measuring both AC and DC leakage current.
• Highest accuracy compared to other methods.
• Potential leakage through a human body via measuring device.

• Direct comparison with measurements made in accordance with IEC 60601-1.       

To consider

• The 1KΩ resistors forming the Measuring Device is interrupting the low resistance earth conductor thus causing potential hazard when testing faulty equipment.
• Secondary earth path(s). The EUT / DUT must be positioned electrically isolated from earth during the measurement. A lower leakage might be measured as not all leakage is measurable in the earth conductor.
• Secondary connections are typical with:
• Equipment bolted to steel enforced concrete floor (eg dentist chairs, MRI)
• Equipment connected to gas or water supply
• Equipment part of a Medical Electrical System
• Equipment connected to PC / Printer

• A difference in Polarity of the Live and Neutral conductors might alter the leakage readings, as such leakage measurements must be done in each polar­ity of mains supply
• A TN (Terre -Neutral) system is required to ensure that the measurements are done at maximum Live to Earth voltage. Any voltage between Neutral and Earth might result in a lower reading, potentially passing faulty equipment.

The Differential method           

The Differential Leakage Method measures the leakage current as a result of imbalance in current between the Live conductor and the Neutral conductor. Potential secondary earth connections are included in the total measurement and as such, the EUT doesn't require to be positioned isolated from earth. Low leakage currents of less than 75µA are difficult to measure using the Differential Leakage method. As such the Differential Leakage method is deemed unsuitable for measuring conductive un-earthed parts and in those instances where leakages are expected to be below 75µA.

Benefits

• The measurements are not influenced by secondary earth connections.

• It measures the total equipment leakage current.
• The measuring device (1KΩ resistor) is no longer in series with the earth conductor, thus providing a low resistance protective earth.

To consider

• The Differential Leakage measurement is less suitable to accurately measure lower leakage currents. (<100µA)
• The measurements are influenced by external magnetic<