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Thoughts on 3M max tails protection with SPD & isolator in tails?

justinneedham
DNO allowance for tails protection from their fuse is commonly 3M. - 3M is deemed AFAICT to extent through any in-line isolator, whether or not that isolator is property of DNO or is consumer fitted part. (The latter is not spelled out by DNO SSEPD who  just state the 3M tails figure without further qualification).
If said isolator begins to sprout additional complexity such as MCB and SPD as a shunt addition, my interpretation (Definitions, part 2) is that it still doesn’t yet qualify as a consumer unit, hence the 3M rule could be said to still run straight through it as far as the farthest CU.

- Any thoughts?

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    Sparkingchip:

    So we can use the DNO main fuse to protect up to three metres of meter tails.


    But presumably that is from the actual fuse, so includes the tails into the suppliers meter as well as the tails out to the consumer unit. . . 




    Not quite. The distance is measured from the outgoing (load) terminals of the meter, or the outgoing terminals of the isolator where this has been provided by the supplier. 


    Regards,


    Alan. 

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  • 0

    Sparkingchip:

    So we can use the DNO main fuse to protect up to three metres of meter tails.


    But presumably that is from the actual fuse, so includes the tails into the suppliers meter as well as the tails out to the consumer unit. . . 




    Not quite. The distance is measured from the outgoing (load) terminals of the meter, or the outgoing terminals of the isolator where this has been provided by the supplier. 


    Regards,


    Alan. 

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