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Supplementary bonding

MrJack96
ff4dd4e3be3fd92a2860545df50ddca9-huge-5418b436-fc4e-47b3-a594-4fea60cb12cd.jpgI see this a lot on sites where they’ve got an armoured cable with an earthing ring/banjo connecting the armour to an extraneous conductive part. Should there also be main bonding run as well? Common thing I see is cable tray being supplementary bonded of a local isolator usually 6mm or 10mm?
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    The so reason for main bonding being such a large conductor is due to the earth resistance being taken as fairly low so high fault current?

    Bonding size is only partly down to fault currents from within the installation and its impedance to earth - some extraneous-conductive-parts (think old metallic water and gas pipes or structural steelwork in a multi-premises building) are quite capable of importing fault voltages/currents from other installations or indeed in the case of PME systems quite significant diverted neutral currents without any faults at all.

       - Andy.
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    The so reason for main bonding being such a large conductor is due to the earth resistance being taken as fairly low so high fault current?

    Bonding size is only partly down to fault currents from within the installation and its impedance to earth - some extraneous-conductive-parts (think old metallic water and gas pipes or structural steelwork in a multi-premises building) are quite capable of importing fault voltages/currents from other installations or indeed in the case of PME systems quite significant diverted neutral currents without any faults at all.

       - Andy.
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