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Overvoltage and Surge Protection for a house in Malta with 3 phase 63A supply

wpqs

I would appreciate some comment on the design of Overvoltage and Surge Protection for a house in Malta with 3 phase 63A supply (see below), particularly the need for a MCB in DB-A to protect the cable running to the MCB in DB-X. This seems like overkill. It was originally specified as a Type B RCD. What are your views? Any other comments are welcome.

Notes:

1. The cables to supply the house run along the facades of the houses in the street, so it seems sensible to protect against lightening strike or other - hence the surge suppressor

2. Overvoltage protection is needed as otherwise the house insurance is void. The concern relates to loss of neutral connection,

3. Malta follows IEE Wiring Regulations, but has some local variations

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  • 0

    First off, what's the earthing arrangement? (I've a vague recollection that Malta may use TT and you diagram might be read as suggesting the same).

    If it is TT you need to be very careful about the possibility of earth faults upstream of the first RCD - generally everything need to be the equivalent of double or reinforced insulation - which might be tricky if the cabling between DBs contains a c.p.c. (or worse, armour). Also check that the SPD is CT2 rather than CT1 (i.e. has the line SPD elements connected to N rather than PE, with usually a gas-discharge type between N and PE). At least one RCD close to the origin (even if just downstream of the SPD etc) may well have its merits.

    UK convention is typically to use a plain switch disconnector rather than an overcurrent protectice device as the incomer in a CU, so relying on upstream overcurrent protection, but that's not universal. In the Irish republic for instance, a B63 is commonly seen as an incomer (or a 63 fuse in older installations) - both approaches have their swings and roundabouts.

      - Andy.

  • 0 in reply to AJJewsbury
    AJJewsbury said:
    UK convention is typically to use a plain switch disconnector rather than an overcurrent protectice device as the incomer in a CU, so relying on upstream overcurrent protection, but that's not universal. In the Irish republic for instance, a B63 is commonly seen as an incomer (or a 63 fuse in older installations) - both approaches have their swings and roundabouts.

    Those two MCBs are not going to discriminate, but I take the view that tripping should be an exceptional event: if the installation is well-designed and the property is well-maintained, nothing should trip.

    I cannot recall anything tripping in our house over the past 28-odd years.

  • 0 in reply to AJJewsbury

    Malta is indeed largely TT, and very dry and rocky (no actual rivers on the island) so decent electrode resistances can actually be quite hard to attain.

    It will be worth expecting marginal performance.

    Mike

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  • 0 in reply to AJJewsbury

    Malta is indeed largely TT, and very dry and rocky (no actual rivers on the island) so decent electrode resistances can actually be quite hard to attain.

    It will be worth expecting marginal performance.

    Mike

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