When should you replace an old fuse board?

• Rewireable fuses, the ceramic carriers with fuse wire. No RCD protection, and no way of adding it. This is the clearest case for replacement.
• No RCD protection on socket circuits, or on cables buried in walls at less than 50mm. Both are required by current regulations for good reasons.
• Signs of heat: browning or scorching around terminals, a smell like hot plastic, a board that's warm to the touch. Deal with this now, not next year.
• A plastic board in an escape route or under a wooden staircase, current regulations call for a non-combustible enclosure in domestic premises.
• No spare ways when you need a new circuit for a charger, shower, hob or outbuilding.
• Cracked, damaged or badly modified enclosures, or a board somebody has clearly had a go at.

• "It's twenty years old." A sound board with appropriate protection, tested and in good condition, is doing its job. Regulations are not retrospective.
• "It's plastic." An existing plastic board is not unlawful. Position and condition are what matter.
• "It hasn't got the latest devices in it." Arc fault detection and surge protection are worth having in the right circumstances. Neither makes an existing installation dangerous.

The practical difference is fault isolation. With RCBOs, each circuit has its own overload and earth-fault protection, so a fault in the garden lights doesn't take out the freezer, the router and the upstairs sockets at the same time.

You also get surge protection, which is genuinely worth having now that houses contain boiler controls, heat pumps, solar inverters and networking gear. Plus clear labelling, a steel enclosure, and spare ways for whatever you add next.

Most domestic board changes take a day, and the testing either side is the bulk of it. Power will be off for a good part of the day, so say up front if you work from home, have a full freezer, or anyone in the house depends on powered equipment.

Be prepared for the testing to find things. Modern RCBOs are far more sensitive than an old rewireable fuse, so faults the old board tolerated, a damp outside light, a nail through a cable, a borrowed neutral from a 1970s alteration, will show up. A good electrician tells you what's been found and what it costs before doing anything about it.