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Surge Protection requirements

aligarjon

Hi Guys.   Just a bit of advice if possible please  A basic large domestic property with a couple of CU's, one is via a sub-main out to an extension.  I have been asked to change the CU 's as there is no rcd protection. I will recommend surge protection to them as it's easy to do at this stage.  Would just at the intake position be enough or better at both.  Thre sub-main currently comes out of the first consumer unit.  If i do it that way i suppose 1 device covers everything. However if space allows i might split the tails and fit a switchfuse, in which case would that section want its own, and if so where.  My gut thought would be to fit one in each CU .

Gary

  • 0

    It all rather depends where you think the surges you are trying to trap are coming from  - if the answer  is down the mains from outside, then the place to knobble them is at the origin, and if done well that is enough.

    If there are loads in the outbuildings that will also create spikes and surges, such as big motors or welders, then do it there too. If the sub-main is so long and exposed that it is an antenna that will pick up atmospheric events like distant lightning, in the same way that the DNO overhead lines do then maybe you need both for that as well.

    I realise that is not a simple yes/no answer, but it should explain why there isn't one for all situations.

    Mike.

  • 0

    On runs of more than 10m from an SPD you can get resonance effects (which I don't profess to understand - maybe Mike can explain it!) which can double the peak - so if the spike is clamped to 1.5kV at the first CU, it may be 3kV at the second CU. So a good rule of thumb is to SPD every DB in the absence of any more specific information.

  • 0 in reply to mapj1

    Thanks Mike.  I have just come back after having a quick look to quote.  The whole job is far from straight forward from what i can see.  They have only just moved in, this is the place i looked at just before Christmas where they were getting shocks from a metal light switch. Since then they have found a further 2 consumer units , their origins unknown, or at least not obvious or labelled. There is also a supposed 30amp supply to detached garage, origin not obvious from labelling. All this and they work from home so i haven't been able to switch anything off to investigate.   Looks like an EICR is in order first.  Neutral face   I am sick to death of EICR'S .  Oh and they are talking car chargers as well, i haven't done any of those yet.   Suppose i better do some research.  :)

  • 0 in reply to wallywombat

    Thankyou

  • 0 in reply to aligarjon

    There is an argument to say that we should not be fitting SPDs in ordinary domestic installations simply because they don't really help that much. For commercial or other high risk areas then fair enough.

  • 0 in reply to aligarjon

    Have you tried the Martindale Fuse Finder? Very useful in these situations, and very reliable. I labelled two large dis boards in a 24 room hotel spread over four floors in a day, with a helper at the other end of a radio. It is in the van, so I’ll post it’s part number tomorrow. 

    Regards,

    Alan. 

  • 0

    I will recommend surge protection

    I think BS 7671 requires a bit more than just a recommendation these days. Unless you can do the risk analysis of regulation 443.5 to show that SPDs aren't required, then you can't sign-off your work as complying with BS 7671:2018 without the SPDs.

       - Andy.

  • 0 in reply to AJJewsbury

    Well, there's always the 443.4 [not .3 as I first wrote] 'single dwelling with little to lose' exception, but with an SPD being about £60 and houses these days choc full of LED lamps, TVs, routers, laptops, tablets, mobile phones, digital boiler controls etc, I can't see that it applies much if at all.

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