• The system contains equipment that introducing a small 'below threshold' amount of neutral earth leakage, and the cumulative effect of the relay check can cause unpredictable nuisance tripping of RCD's. Some common troublesome appliances to check and disconnect first when troubleshooting are surge Protected Power-boards, old refrigerator compressors and electric hot water units (due to their own earth differential from the main earth stake). 6.2 Mobile or independent installations A mobile or independent installation is an installation that is operating independently from the grid or regular mains power. For example, like in: • Boat Please note that in this chapter we speak about a boat installation, however this text can also be used for any mobile or independent installations, including automobiles. In a mobile application situations can exist that do not occur in a common, grid connected, house installation. In this chapter we recognize 2 different situations: • A mobile installation is connected to mains or shore power (Situation 1) • A mobile installation is disconnected from mains or shore power and is using a generator and/or an inverter (situation 2) Situation 1 • Automobile • Campervan • Off-grid installation.
When a boat is moored and connected to shore power, the situation on board is almost the same as if this installation was a residential installation. There is only one difference; the boat does not have its own earth connection like the earth spike you will find in a house. The boat installation relies on the earth provided by the shore connection. Unfortunately, this earth is not always reliable due to the fact that the marina cables are often long and have an insufficient cable core thickness.
To create a safe situation, the metal parts of the boat, like the hull, will have to be connected to the incoming earth from the shore power cable. The shore power earth is connected to the star point of the mains distribution and is part of mains power. In this situation 2 separate electric circuits are possible thus allowing for the proper operation of a RCD. If an earth leakage occurs, current can flow though the earth conductor in the mains cable, but also via the hull trough the water and back to shore earth. Both earth leakage circuits have got the same potential and are in a way connected in parallel, but in the event of an earth leakage fault, more current will flow through the earth conductor in the shore cable, because the path through the hull and the water has got a bigger resistance. Situation 2
As soon as the boat disconnects from shore power the entire installation changes because the installation is not part of the mains anymore and the connection with the star point of the mains is lost. The installation has got its own energy supply and together with the loads forms its own electric circuit. No current will flow into the hull and into the water.
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