Stroma Certification Scheme What RCD for 18th Edition

[Julie.]

Would the SPD not be on the supply side in most scenarios?

Yes, as said above, you don't really want a rcd/rcbo upstream of a spd; the spd works by shunting current neutral-earth/cpc and line-earth/cpc so the rcd could operate.

The rcd wouldn't operate quick enough to inhibit the operation of the spd, but would remain tripped after it, so a subsequent surge wouldn't be protected against by the spd as it would be out of circuit.

Most spd are direct on the busbar being protected by the main incoming fuse, or have a dedicated mcb or fuse (unusual these days) within the cu.

Fuses are more common on large industrial sites where the incoming fuses are several hundred amps and three phase.