Why not one big circuit
A single circuit feeding a whole flat looks cheap and works until something goes wrong. Then one fault takes down everything: the fridge, the router and the light you need to find the panel in the dark. Fault-finding becomes guesswork, because the fault can be anywhere behind one breaker. And a breaker sized for the whole flat is far too coarse to protect the thin cable running to a ceiling lamp.
Splitting the home into circuits buys three things: a fault stays local, each cable gets a breaker that actually matches it (cable cross-sections), and you can work on one circuit with the rest of the home live.
Light and sockets stay apart
Lighting and socket circuits are separated for a practical reason: when a socket circuit trips, the lights must stay on. Lighting also draws little current, so it runs on 1.5 mm² with a 10 A breaker, while sockets need 2.5 mm² and 16 A. Mixing them forces the thin lighting cable under a breaker that is too large for it.
Socket circuits are limited by load, not by a socket count in a standard. A rough working estimate is 300 W per socket point and 100 W per light point, which is what PlanMyPanel uses. In practice that puts around five or six socket points on one 16 A line before it becomes worth splitting.
Kitchens and bathrooms
- Kitchen. The kettle, microwave and toaster together can exceed a whole living room's peak, so the kitchen gets its own socket circuits instead of borrowing the hallway's.
- Bathroom. Wet rooms are a shock hazard, so their sockets and their lighting go on separate circuits with 30 mA protection (why 30 mA).
- Big appliances. A stove, oven or water heater never shares a socket circuit; each gets a dedicated line.
How the app groups rooms
PlanMyPanel builds groups from your room list. Dry rooms are packed into shared lighting zones up to about ten light points per circuit; wet rooms get their own lighting zone so it can sit behind a 30 mA RCD. For sockets, any wet room and any room with more than two socket points gets its own line; small dry rooms (two points or fewer) are packed together up to six points per circuit. Every heavy appliance you tick becomes a separate dedicated group.