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Selection of MCB for SPD protection

Julien Leblanc
Hello,

I need to install a type 1+2 SPD into the main panel of a small business building, which needs lightning protection.

The main breaker in the main panel is a 4 poles 40A MCB.

I was looking for a SPD and I found this: Schneider A9L16634.

In the technical specification sheet it says "Associated circuit breaker NG125N 80A curve C - Icu 15 kA".

I was wondering why the associated breaker needs to have such a high current (80A)? It seems i cannot ensure the selectivity of the breakers.

Could anyone explain what can happen if i use a smaller breaker, for example a 32A one for the protection of the SPD?


Thank you.




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    whjohnson:

    The interesting thing is that there is no protective device - the SPD tails are wired directly into the bottom of the main switch.




    Sounds like a similar arrangement to the Wylex ones. These have a built-in (presumably) spring-loaded fuse which when blown causes the window to turn red: because of the fuse, it doesn't require its own breaker as long as the upstream CPD is <125A

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  • 0

    whjohnson:

    The interesting thing is that there is no protective device - the SPD tails are wired directly into the bottom of the main switch.




    Sounds like a similar arrangement to the Wylex ones. These have a built-in (presumably) spring-loaded fuse which when blown causes the window to turn red: because of the fuse, it doesn't require its own breaker as long as the upstream CPD is <125A

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