Electric heaters and a flat’s wiring

A flat’s typical electrical supply diagram consists of an input circuit breaker, an energy meter, a residual-current protection device, and sockets and switches in rooms. Before wiring, we find out where the supply is, where and what the consumers are, how wires run, and where switches and sockets go; then the circuit diagram is drawn. To connect one lamp, current goes from the source through the switch and lamp holder and back to the source: closing the switch lights the lamp. Several lamps are connected in parallel: each gets the same voltage, so if one goes out the others stay lit. A switch with two or three keys lets each lamp be lit separately. Wire cross-section is chosen by the consumer’s power: current is found by P : U, and the greater the power, the thicker the wire. Real wiring of a flat is done only by a qualified electrician, because one unreliable connection can cause a fire or injury; even changing a lamp is done carefully, with the switch off first. At school, wiring is done on a flat model with a low-voltage source (a battery up to 12 V), supervised by the teacher. Nothing is ever pushed into a mains socket, and switches and sockets are not touched with wet hands.