The consumer unit main switchWill a main switch ever trip?

Our simplest board is just an enclosure with a main switch. The switch is marked BS EN 60947-3, the common standard for an isolator (switch-disconnector). This one is rated 100 A.

• On-load isolator: the symbol has little circles at the contacts, so it can be switched on and off with load connected. An off-load isolator has the same symbol without the circles and should only be operated with no load.
• Not a circuit breaker. It's rated to carry 100 A. Push more through it and the contacts will overheat and maybe melt, but it won't trip.
• "My main switch tripped!" In that case it was a different device: a BS EN 60947-2 switch has a protective device built in and can trip under fault. A 60947-3 won't.
• It's a double-pole, or linked, main switch: line and neutral are switched together. This is needed so the whole installation can be isolated.
• On this board, supply side (top): the meter tails, line and neutral. Load (busbar) side (bottom): a solid copper busbar screwed into the line, and a thick neutral cable up to the neutral bar.
• That's how it comes out of the box. You can take it apart, but Sparky's tip is leave it alone. Some people cut the busbar shorter. On this board the bar is also held by a plastic grip, so cutting it would stop that working, go against the manufacturer's instructions, and could void the warranty.

BS EN 60947-3 · isolator / switch-disconnector (no trip) BS EN 60947-2 · circuit-breaker type (can trip)

BS 7671 · requirement for a linked main switch Reg 462.1.201 (Chapter 46, isolation and switching) · check your copy