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Can a DNO Service Cut-out be used as the primary source of fault current protection, when the DB it supplies is more than 3m from the intake?

Dill Jotter

I attended a site where the DNO (100A 1361) feeds a 100A Sw/ disconnector (with solid un-fused links) this then supplies a DB located in an adjacent room with 100A 60947-3 main switch.

Is this acceptable as the only fault current protection is afforded by the DNO. 

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    Physically, it's probably OK (provided all loop impedances are reasonable, TN system etc.)

    Compliance wise, it's more difficult - BS 7671 only allows omission of fault protection for up to 3m (with other conditions), so you're reliant on the the DNO agreeiing that their fuses provide protection ... so you'll have to ask them. Usually they either refuse alltogether and advise relying on BS 7671's 3m rule, or set their own limist (which is frequently 3m or thereabouts), but your milage may vary.

        - Andy.

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  • 0

    Physically, it's probably OK (provided all loop impedances are reasonable, TN system etc.)

    Compliance wise, it's more difficult - BS 7671 only allows omission of fault protection for up to 3m (with other conditions), so you're reliant on the the DNO agreeiing that their fuses provide protection ... so you'll have to ask them. Usually they either refuse alltogether and advise relying on BS 7671's 3m rule, or set their own limist (which is frequently 3m or thereabouts), but your milage may vary.

        - Andy.

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