Page 263 - Electrical Safety of Low Voltage Systems

246 Chapter Fifteen

FIGURE 15.2 Connection of the vessel to a single-phase, shore-mounted
isolating transformer.

15.3 Electrical Safety Requirements for Equipment
Having High Protective Conductor Currents
Electronics equipment (e.g., computers, telecommunication equip-
ment,etc.)maybesensitivetoelectromagneticinterferencesirradiated
by “disturbing” loads. For this reason, radio frequency input filters
constituted by capacitors connected between supply conductors and
enclosures of equipment are employed to enhance the electronic sys-
tems’ immunity. Such filters may cause continuous leakage currents
through the protective conductors in excess of 3.5 A (Fig. 15.3).
3
International standard IEC 60950–1 limits the maximum value of
leakage currents of Class I, stationary, or pluggable, equipment to 5%
of the input current. The presence of high currents on protective con-
ductors might cause nuisance trippings of RCDs, when their residual
settings are exceeded even in the absence of ground faults.
Serious hazard is caused by the accidental loss of the protective
conductor serving the equipment (Fig. 15.4).

FIGURE 15.3 Earth
leakage currents
due to radio
frequency filters.