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What are the requirements for a consumers main switch on a TPN 200A new supply ? Can the tails from the metering go straight into a panel board with a 4 pole 200A MCCB as the main switch, or do you have to install a separate isolator

KRB15

The new mains cut out and metering are being installed shortly , this will feed a 250A Panel board adjacent to the service head. The panel board will have a four pole 200A MCCB as a main switch and will therefore isolation all of the upstream installation. It seems pointless installing a separate main switch but will the supplier accept this and will it comply. UKPN and the electricity supplier  are sitting on the fence , well they would be if you could talk to anyone !

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    Does the size of the supply matter?

    Given that a separate isolator is not required on the domestic scale, I assume not.

    However, it is convenient to install one, because it then leaves you free to do anything inside the panel board, or even replace it.

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    I would have thought it was a BS 7671 matter rather than the DNO's (their responsibility mostly stops at the cut-out terminals) or supplier's (after metering). The only time I can think of where DNO specifications are relevant is where you're depending on their equipment - e.g. their main fuse for overcurrent protection - for which they tend to specify things like min c.s.a. and max length of conductors and such like.

    As with many things, BS 7671 allows designers quite a bit of latitude to do things how best suit the particular situation and their customer's requirements. There are advantages to having a separate isolator upstream of the main board - e.g. it allows the main board to be conveniently isolated for periodic inspections & tests, alterations or even replacement. It is always possible to use the DNO's cut-out for isolation, but that usually has to be done by DNO or supplier's personnel and at their convenience so tends to cost the customer both time and money when it's necessary. In the domestic world where a single call out can be in excess of £100 and a DP "REC" isolator available for about £20 it's a bit of a no-brainer to fit one at the first opportunity to my mind, but it's not a requirement and many a supplier don't fit them by default.

       - Andy.

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    Just spotted this - apologies for the late reply.

    I have seen installations in the UKPN area exactly as you describe - panel board with MCCB main switch fed directly from the cut-out (CT metering). Cables in 100x100 metal trunking for neatness and protection.

    Having an isolator in between obviously has some benefits as Andy said. Disadvantage is that an 200A isolator is large and expensive, also it's another possible point of failure.

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