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Testing if supplementary bonding is required.

MrJack96
I have read some bits stating we can measure between the two metallic parts in question and referring to the formula 


50/ia will give you the resistance needed to keep touch voltage to less than 50v 


my questions can we do the same test to determine if the part has a high enough resistance to not require bonding and what sort of figures we should look for?
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    MrJack96:

    Am I right in saying in both cases (broken PEN)the installation should be safe only considering all bonding requirements have been met? The only issue is outside the Equipitential zone? That’s why in some cases it’s not a good idea to bond outside taps due to the fact if the Met was at 230v within the installation the tap would then be at the same potential meaning the folk who ends up touching this will be in a dangerous scenario?


    Indeed - the risk from an outside tap with a TT system is small as disconnection should occur reasonably rapidly - certainly within 1s under current regs - but for a PME system where a broken PEN condition might exist for days or weeks, an insulating insert in the pipework feeding an outside tap is often recommended (or better still these days, entirely plastic pipework). The same can apply for Class I (earthed) appliances outdoors - e.g. outside lights and for the same reason the vast majority of electric garden tools are Class II (double insulated).


       - Andy.


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  • 0
    MrJack96:

    Am I right in saying in both cases (broken PEN)the installation should be safe only considering all bonding requirements have been met? The only issue is outside the Equipitential zone? That’s why in some cases it’s not a good idea to bond outside taps due to the fact if the Met was at 230v within the installation the tap would then be at the same potential meaning the folk who ends up touching this will be in a dangerous scenario?


    Indeed - the risk from an outside tap with a TT system is small as disconnection should occur reasonably rapidly - certainly within 1s under current regs - but for a PME system where a broken PEN condition might exist for days or weeks, an insulating insert in the pipework feeding an outside tap is often recommended (or better still these days, entirely plastic pipework). The same can apply for Class I (earthed) appliances outdoors - e.g. outside lights and for the same reason the vast majority of electric garden tools are Class II (double insulated).


       - Andy.


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