5 A fuse box 30 A 5 A 15 A 30 A cooker lighting circuit immersion heater
ring main circuit two-way switches
13 A socket FIG. 29.1 Internal domestic wiring is split into a number of circuits Faults/safety features
Because electricity can be dangerous, many precautions are taken to ensure domestic supplies are safe.
Switches Rather than have all appliances constantly connected to the live, switches are used to connect or disconnect an appliance when needed.
Fuses
Fuses are connected in the live and protect against too much current flowing. Since current has a heating effect, too much current will cause the fuse to melt and break the circuit.
The value of a fuse should be slightly above the expected current value. Because of this, if the current unexpectedly rises above this, the fuse will melt and break the circuit to avoid major accidents. When calculating fuse values, always allow for a fuse rating just above what is needed for the normal current load. For example, if the current is expected to normally operate at 2.7 A, use a 3A fuse.
