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Surge protective devices — section 534Type 1, 2 or 3. Which SPD goes where?
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Everything the exam can ask you about SPDs lives in section 534. Two things in there are worth tabbing.
LPZ — lightning protection zone
The section opens with a figure showing lightning protection zones and what you'd install for each zone around your equipment. Worth recognising the abbreviation; you're unlikely to be asked to reproduce the diagram.
The three types, and where each one goes
| Type | Where it goes |
|---|---|
| Type 1 or 2 | At or near the origin of the installation — i.e. in the main distribution board |
| Type 2 or 3 | Further along, e.g. at a sub-board, where it is beyond the origin SPD's protective distance |
| Type 3 | Close to sensitive equipment, where the equipment needs it |
A typical domestic board carries a type 2, marked in capitals inside the enclosure. "Near the origin" doesn't mean inside the box: you'll see boards with a separate SPD enclosure sitting alongside, which is still at the origin of the installation. Others sit in their own little box inside the board.
Also worth knowing: there is no map of lightning-strike frequency in the regulations book, so don't go hunting for it. The design point survives: if you're in an area that takes a lot of strikes, you're more likely to need protection.
534 · measures against overvoltages · SPDs, types 1, 2 and 3 ★ 443 · transient overvoltage (Part 4, Part 1) Part 2 · "surge protective device" definition
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