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origin of the installation

Dave Miller

please forgive this daft question, and I accept that I may be reacting to a non-existent problem

if I'm reading the wiring regs correctly, then we can protect the origin of an installation against overcurrent (whether overload or fault) by using the distributor's protective device with their consent. However, I can't see an equivalent provision to protect the origin of an installation against electric shock by similarly using the distributor's protective device for automatic disconnection of supply

I'm thinking of industrial supplies where the meter is in a substation at the edge of the site and the main DB is in a building on the other side of the car park, so the only protection for a couple of hundred yards of incoming cable is whatever the distributor has fitted at the substation

  • 0 in reply to mapj1

    sorry if I wasn't clear

    this leads back to my question. there's a metered breaker in the substation owned by the distributor which is the end of their responsibility and which protects the customer's cable across the car park to the customer's main DB. the wiring regs explicitly allow us to use the distributor's metered breaker for overcurrent protection of that cable, but are silent on whether or not we can use that breaker for ADS to protect against electric shock

    I'm confident that I can persuade the distributor to let us use their metered breaker to protect this cable. I'm confident that we can find settings to meet the 5s disconnection time which I think is the relevant benchmark for ADS in the wiring regs. I'd just like to tie this off with a ribbon by being able to quote the right bits of the wiring regs that say that it's OK for us to rely on the distributor's breaker to protect the customer's cable across the car park (and their metal-clad main DB where that cable terminates) against electric shock as well as to protect against overcurrent

    Dave

  • 0 in reply to Dave Miller

    In this regard, it would be the responsibility of the duty holder to ensure that the EAWRegs were met with respect to Regulation 4, 5, 8 and 11. The application of, inter-alia, regulations 411.4.4, 433.3.1 (iii) and 434.3 (iv) of BS 7671 might assist in demonstrating compliance with the statutory provisions but would require a reasonably detailed assessment of the arrangement.

    However, it would seem sensible that the setting of any protective device should be at the discretion of the duty holder rather than the DNO. 

  • 0 in reply to Dave Miller

    the wiring regs explicitly allow us to use the distributor's metered breaker for overcurrent protection of that cable, but are silent on whether or not we can use that breaker for ADS to protect against electric shock

    That's a good question - and one that could do with answering, since the switch to steel enclosures for domestic CUs we're de facto relying on the DNO's fuse for ADS for faults within the CU (before the outgoing protective devices).

       - Andy. 

  • 0 in reply to lyledunn

    yes, all agreed

  • 0 in reply to AJJewsbury

    thanks, Andy

    I'm glad I'm not completely barking

    good point, the same question arises for a few metres of meter tails to a domestic consumer unit or a few hundred yards of cable to a large industrial 400V switchboard

    common sense says yes we, can. a tricksy lawyer might argue that if the fine engineers who wrote the wiring regs meant it then they would have written it in

    Dave

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