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Multiple Earth Electrodes TT System

Steve UKBC
Thoughts or suggestions welcome....


Is there any issue or downside to having multiple earth electrodes installed on a single TT system (all areas have there CPC connected together) when the TT system spans a large area (we are taking about a 400m x 400m area)?


For example


If you had a couple of farm barns/sheds (metal framed) close together with multiple earth electrodes and some few hundred meters away you have a camp site with multiple earth electrodes (one at each power outlet etc) and then connect the CPC from the barns to the camp site to make one large TT system?



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  • 0
    Would you suggest using 2 rather than one RCD just after the DNO cutout (identical RCD's different manufactures) could be a way forward to protect against this or would this just be over engineering, considering the size of installation?

    There's nothing official that suggests that duplicate RCDs is necessary or even recommended - although it happens 'by default' as it were in a number of situations - often a TT install will have a 100mA-S type (or higher) as an incomer and then 30mA protection for final circuits - should the final circuit RCDs fail then the incomer can act as a backup - usually providing perfectly adequate ADS (although not additional protection) to the final circuits. As most L-PE faults tend to occur in appliances or final circuits rather than in switchgear or distribution circuits, that sort of thing pushes the probabilities quite a long way in the right direction. In some high risk situations - e.g. caravans - the separate requirements for 30mA RCD protection at the pitch and within the caravan again result in duplication.


      - Andy.

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  • 0
    Would you suggest using 2 rather than one RCD just after the DNO cutout (identical RCD's different manufactures) could be a way forward to protect against this or would this just be over engineering, considering the size of installation?

    There's nothing official that suggests that duplicate RCDs is necessary or even recommended - although it happens 'by default' as it were in a number of situations - often a TT install will have a 100mA-S type (or higher) as an incomer and then 30mA protection for final circuits - should the final circuit RCDs fail then the incomer can act as a backup - usually providing perfectly adequate ADS (although not additional protection) to the final circuits. As most L-PE faults tend to occur in appliances or final circuits rather than in switchgear or distribution circuits, that sort of thing pushes the probabilities quite a long way in the right direction. In some high risk situations - e.g. caravans - the separate requirements for 30mA RCD protection at the pitch and within the caravan again result in duplication.


      - Andy.

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