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1.1.6 Common mode disturbances in the frequency range 0 Hz to 150 kHz
IEC 61000-4-16 Ed.1 Amd.2
The conducted, common mode disturbances at mains frequency and its harmonics may be generated by
faults on the mains power distribution system and leakage currents flowing into the earth system. The d.c.
power supply network used in industrial, electrical plants and telecommunication centres may also
generate d.c. common mode disturbances, particularly when either the positive or negative terminal is
connected to earth.
Electrified railways will also generate disturbances at their frequency of operation (typically 16
2/3 Hz).
The induced disturbances are described in detail in IEC 61000-2-3 and IEC 61000-2-5. The different types
of disturbances may be present simultaneously but at different levels.
Furthermore, if the power system develops a fault, the disturbance levels may be up to 10 times the
reference levels given for normal operating conditions, however the fault condition disturbances are
typically present for short durations only (up to about 1 s).
The disturbances at mains frequency and harmonics may affect signal ports of equipment where
insufficient common mode rejection is available. Disturbances up to 1-2 kHz are mainly due to the
harmonics of the power mains.
At higher frequencies the disturbances are mostly related to power electronic equipment, which may
produce switching currents involving the ground system, giving rise to conducted, common mode
disturbances.
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