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Did the SPD work?

Northern Spark

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?

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  • 0
    Northern Spark said:
    Did the spd work?

    I think by definition, no.

    Suppose that the SPD achieved nothing. It would not trip its 32 A type B MCB. It would not protect the installation. You have not specified whether the smart speaker was on the circuit which tripped. However, the surge would might have led to an over current through the circuits and trip their MCBs.

    I have to confess that I do not fully understand why an SPD has OCPD. As I understand it, the SPD can withstand multiple over voltages, but if it shorts (for want of a better word) the MCB will trip. If I have that wrong, please say so.

  • 0 in reply to Chris Pearson

    Smart speaker was on the circuit that tripped.

  • 0 in reply to Northern Spark

    From reading the Beama guide on SPDs, Could it be you have a type 2 SPD, which can handle common mode surges. But if the surge was a different kind, a differential mode surge, the SPD may have failed to shield your devices ? You may need to get a type 3 SPD, which can deal with differential mode surges, and plug it in where the speaker is as it’s likely classed as sensitive equipment. 

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  • 0 in reply to Northern Spark

    From reading the Beama guide on SPDs, Could it be you have a type 2 SPD, which can handle common mode surges. But if the surge was a different kind, a differential mode surge, the SPD may have failed to shield your devices ? You may need to get a type 3 SPD, which can deal with differential mode surges, and plug it in where the speaker is as it’s likely classed as sensitive equipment. 

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