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LV Tails

Karl Barfoot

I need guidance on a recurring issue we face in our projects:

 

In accordance with BS7671, we advise installing consumer protective devices if the tails exceed 3 meters in length. This is because the Distribution Network Operator (DNO) cannot guarantee fault protection for cables over this length.

 

My question is whether to opt for an uplifted agreed connection, which would entail additional cost for the customer but ensure discrimination between DNO and consumer equipment. Alternatively, should we recommend installing both with the same rating switch-fused isolator and hope for the operation of consumers equipment?

 

While I can address LV network overloads downstream using electronic devices and as a main switch, direct fault protection on the tails could trigger either device.

 

Your insights on the most effective approach would be greatly appreciated.

  • 0 in reply to AJJewsbury

    well if it is 300 amps plus it won't be metered 'whole current' but with CTs or more likely not at all until after splitting down into a Ryefield/Lucy splitter, and assuming the kind that is made for multiple single phase supplies to  flats and so on, the largest fuse they take is indeed 100A per output.

    If extending the 300 A side to somewhere more convenient, then something more than 25mm tail is in order.

    M

  • 0 in reply to mapj1

    I think it is the supply side of the Ryefield that Karl is talking about (initially I mis-read/assumed it was the load side, hence the comment about the Ryefield belonging to the BNO).

       - Andy.

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