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I've been installing Type 2 SPDs in consumer units for several years now, and they always come as a pair, connected across L & E, and across N & E. Typically they plug into a holder, sometimes as two separate SPDs (e.g. Hager, with separate E connections), more often now as one combined SPD (e.g. Fusebox) with one each of L, N & E connections.
For a TN-C-S supply where N & E are typically connected a very short distance way (e.g. well under 3m), can someone tell me why the SPD across N & E is actually needed?
I can see the merit for TT and maybe TN-S supplies, and wonder is it just to simplify making only one devices that will serve all applications?
Do single module Type 2 SPDs for use across just L & E actually exist?
For a TN-C-S supply where N & E are typically connected a very short distance way (e.g. well under 3m), can someone tell me why the SPD across N & E is actually needed?
I can see the merit for TT and maybe TN-S supplies, and wonder is it just to simplify making only one devices that will serve all applications?
Do single module Type 2 SPDs for use across just L & E actually exist?