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BONDING.
Large lamps, have inevitably metal parts and will be bonded to earth. But this can conflict with the normal low-voltage (PELV) system.
Further: a problem can arise when the installation is large and connecting to the earth happens over a wide area. Over a longer distance a potential difference can occur between earth on one place and earth on another place, especially with dry soil.
This means ignition hazard and immediate danger!
It is clearly very important that the responsible operator must specify the dangers of potential differences.
IF YES: THERE IS A DANGER:
1. SELV, 3p: connecting the lamp through a three core wire with the low voltage transformer.
The bonding is connected through the third wire to the third pole of the transformer sockets. The transformer has its own local bonding by a earth cable and C-clamp.
Lamp and its accessories are bonded through the cable. The transformer is first bonded and then powered.
Result: no ignition hazard due to static electricity because the potential of metal parts of the system is definitely the same as vessel has.
OR: 
2. SELV, 2p: connecting the lamp through a two core wire with the low voltage transformer.
No bonding through the wire or socket. Bonding of equipment and extraneous
metal parts has to be taken account at the place use of ELV-equipment.
If the lamp has metal parts or has metal accessories then these items must be bonded by an individual cable directly from the this item. Only after making this connection, the lamp may be powered.
Result: no ignition hazard due to static electricity because there is no metal parts in the system or extraneous metal parts are bonded to the vessel one by one.
IF NO: THERE IS NO DANGER OF POTENTIAL DIFFERENCES: 
1. PELV, 2p+E: connecting the lamp through a three core wire with the low voltage transformer.
Earth pole of the socket is for earthing of the equipment and extraneous metal parts.
The lamp and its accessories are earthed by the supply. Lamps and supply have the same potential as the local work area earth, as established by the operator.
Result: no ignition hazard due to static electricity because the potential of metal
parts of the system is the same as vessel and electrical supply.
OR:
2. SELV, 2p: connecting the lamp through a two core wire with the low voltage transformer.
No bonding through the wire or socket. Bonding of equipment and extraneous
metal parts has to be taken account at the place use of ELV-equipment.
If the lamp has metal parts or has metal accessories then these items must be bonded by an individual cable directly from the this item. Only after making this connection, the lamp may be powered.
Result: no ignition hazard due to static electricity because there is no metal parts in the system or extraneous metal parts are bonded to the vessel one by one.
Disclaimer:
It is our pleasure to hand you the above information. Please bear in mind, that this is just basic information, for your convenience. For more detailed, checked and up to date information, please contact the relevant authorities, notified bodies or your securrity officer. We exclude any obligation or responsibility regarding the content of this document or of the related website.
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