Did the SPD work?

Domestic installation. PME supply. 50A type b mcb in meter cupboard, 16mm armoured to consumer unit in house. BG consumer unit with type 2 SPD.

There was a power cut, and seemingly a network born over voltage(a neighbour reported that their type 3 spd incorporated into a plug board operated). Unclear wether the over voltage was when the power failed or when it was restored. The 50A mcb in the meter cupboard and a 20A type b rcbo in the consumer unit protecting the kitchen socket circuit both tripped. The 32A type b mcb protecting the spd did not trip. A day or two later the customer noticed that their google nest mini smart speaker(other smart speakers are available) was not working and discovered its plug and the socket it was plugged in to were charred. It was plugged into a socket that is probably the closest one to the consumer unit. The spd indicator remained green. No other signs of damage to anything.

Did the spd work?

Why did the 50A and 20A breakers operate, but not the 32A breaker protecting the spd? If the spd works, shouldn't it shunt the fault current and therefore trip its breaker?

  • Interesting stuff, thank you all. So it would seem likely it was a 'low' over voltage. I did also wonder if the SPD being in the consumer unit in the house and not at the source of the installation had anything to do with it.

  • How long before the regs start asking us to fit voltage monitoring relays (like https://uk.rs-online.com/web/p/monitoring-relays/1026131) (and a thumping big contactor) to avoid this problem?

    In a sensible world it could probably just be done with a software update on smart meters (as they already have voltage measurement and a contactor built-in) and arguably would be appropriate for the supply industry to bear the responsibility of ensuring that what they deliver is within spec. however...

       - Andy.

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