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Local Earthing cable size

Nick Parker

What is the IEC code used to determine the size of the earthing cable for the equipment frame grounding to the nearest grounding bar (local bonding)?
This is in addition to the ground cable that runs along with phase conductors from the source to the equipment.

In my case the size of the ground cable which runs from the source is same as that of phase conductor. Should the local bonding cable be same size or be downsized?

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    I suspect the answer is "it depends"...

    Firstly it depends on the purpose of this additional conductor - is it a duplicate c.p.c. to provide enhanced reliability in the case of  high protective conductor currents in normal service for instance (in which case it's normally sized in the same way as the main c.p.c.) or is it for supplementary bonding - in which case it'll likely be minimum half the size of the c.p.c. or if it's effectively connecting two exposed-conductive-parts together, no smaller than the smaller c.p.c..  Then there are mechanical considerations - which likely put a minimum of 2.5mm² or 4mm² depending on quite what level of protection it's given.

    Also there may not be a simple single IEC answer - as this sort of thing often varies between national standards (the above is from the UK's BS 7671).

       - Andy.

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