Mains Electricity – AC Current and Voltage

Mains electricity uses alternating current (AC), where electrons periodically reverse direction. In the UK, mains electricity has a frequency of 50 Hz, meaning it completes 50 cycles every second.

Direct current (DC) flows in one constant direction. Batteries and solar cells produce DC. AC is preferred for mains electricity because it's easier to transform to different voltages for efficient long-distance transmission.

UK mains voltage is approximately 230 V RMS (root mean square). The peak voltage reaches about 325 V, but RMS gives the equivalent DC voltage for power calculations.

Power (P) measures the rate of energy transfer. For electrical circuits:

Energy (E) is power multiplied by time. For electricity billing, we use kilowatt-hours (kWh):

One kilowatt-hour equals 3.6 × 10⁶ joules. To calculate cost, multiply kWh by the price per unit (typically £0.25-0.35 per kWh).

Fuses contain thin wire that melts if current exceeds the rated value, breaking the circuit. Common ratings are 3A, 5A, and 13A. Choose a fuse rated just above the normal operating current.

Circuit breakers automatically switch off when current is too high. Unlike fuses, they can be reset after tripping. Both devices protect against overheating and fire from excessive current.