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What is the difference between DC and AC?

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Electricity comes in either alternating current (AC) or direct current (DC). With direct current two wires are maintained with a steady potential difference between them, measured in volts (V), and when a load is connected between the two wires current flows from one to the other doing work.

The symbol for DC is straight line above a straight dashed line, which represents the fact that the voltage remains fairly constant in a DC system. The system of wires and loads is colloquially known as a network.

However, the vast majority of systems consuming significant amounts of power electrical networks make use of alternating current for generation, transmission, and distribution because with AC we can use transformers to obtain different voltages. In a single-phase AC network the potential difference between two wires oscillates in a sinusoidal manner at a constant frequency.

It so happens that one wire (known as the neutral, N) normally remains at the same potential difference as ground (literally the earth, variously designated E or PE) whilst the other wire (known as the live, L) alternates from being positive with respect to neutral through to being negative.