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Consumer unit IP ratings and blanksIP4X or IPX4 on top of the board?

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As well as being non-combustible, the enclosure must keep an adequate IP rating (International Protection). A consumer unit is an enclosure containing live parts, just like a socket-outlet, so the same minimums apply:

Top horizontal surface: IP4X or IPXXD a 1 mm wire can't get in DIN rail CB RCBO 12543 blanking plate main switch Sides, bottom and front: IP2X or IPXXB a finger can't get in Fixing holes in the back don't count: the wall or panel covers them Every hole you drill or knock out must keep these ratings (glands, grommets, blanks)
Redrawn from our five-way board: CB in way 1 next to the main switch, RCBO in way 2, and a metal blank over ways 3 to 5.
SurfaceMinimumWhat it means
Top horizontal surfaceIP4X or IPXXDObjects ≥ 1 mm (a wire) can't get in. Tops catch dropped items: screws, offcuts, swarf.
Sides, bottom, frontIP2X or IPXXBRoughly a finger: 12.5 mm for IP2X, and the 12 mm jointed test finger, 80 mm long, for IPXXB.
Watch out: IP4X, not IPX4
A common mix-up is saying the top surface must be "IPX4". It should be IP4X: the first digit (solid objects, a 1 mm wire). IPX4 would be splash protection against water, which is a different thing.

Code of Practice for In-service Inspection & Testing of Electrical Equipment ("the PAT testing book") · Appendix 2 · IP codes explained The clearest explanation of IP codes

BS 7671 · Reg 416.2.1 · barriers/enclosures at least IP2X or IPXXB BS 7671 · Reg 416.2.2 · readily accessible top horizontal surfaces at least IP4X or IPXXD

Blanks: keeping the front covered

  • The cover has a slot for the breakers. If a way has no device in it (our five-way board with two circuits leaves ways 3, 4 and 5 empty), the gap must be closed with a blanking plate.
  • Our metal blank hooks in and slides along, and can only be fitted with the cover off. With the cover and breakers in place it's secure and very unlikely to move.
  • You can also get flexible plastic blanks. Make sure the one you fit keeps fingers out and is durable enough for the environment it's in.
  • A spare circuit breaker can be used as a blank. It's allowed. It's just expensive: a pack of 10 blanks costs about £1, one breaker about £3–£4. This comes up a lot.

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