METREL MI 3399, Инструкция с упражнениями

Страница: 230 / 272

PAT Appliances & Machines Safety Trainer AD 3
– MI 3399
230
Scope of test
– leakage currents
With current clamps leakage currents can be measured too. However this measurement
has many serious drawbacks:

Results are not accurate. They are strongly influenced by external magnetic and
electric fields (caused by load currents, big conductive surfaces close to voltage
sources etc). At currents below 10mA the influences can likely make the results
unusable.

Embracing all live and neutral conductors in a single and three phase system would
theoretically return the leakage current. This principle often does not work well in
practice.
Therefore measuring of leakage currents range of several mA cannot be treated as
accurate. A lot of presumptions and experience of the user are needed to obtain relevant
results.
Local regulations must be checked whether the current clamp leakage test results can be
considered as relevant.
Examples of faults for which troubleshooting with current clamp is recommended
Fault:
A propeller of pump is sticked in the fixed installed appliance. High supply currents
are flowing while the pump is supposed to work.
Result: High fault currents can result in dangerous overheating in the appliance. This can
cause fire!
Fault: A powerful heater with high nominal leakage was fixed installed.
Result: Occasional tripping of the RCD. Dangerous contact voltages can occur on
accessible conductive parts if the electrical installation is not designed properly.
Figure 4-26: Functional and leakage problems