Electrical polarity (positive and negative) is present in every electrical circuit. Electrons flow from the negative pole to the positive pole. In a direct current (DC) circuit, one pole is always negative, the other pole is always positive and the electrons flow in one direction only. In an alternating current (AC) circuit the two poles alternate between negative and positive and the direction of the electron flow continually reverses.

Contents 1 Positive and negative 2 Live and neutral 3 Ground (earth) 4 See also

[edit] Positive and negative

In DC circuits (e.g. for a car battery) positive is usually marked red and negative is usually marked black. In AC circuits (e.g. domestic mains supply) polarity markings are not relevant (because the two poles are alternately positive and negative) but wires are colour-coded for live and neutral.

[edit] Live and neutral

It is important not to confuse positive and negative with live and neutral - they are completely different concepts. The old UK house wiring colours were red for live and black for neutral but this does not mean that live is positive or that neutral is negative.

"Live" indicates that an electrical conductor has a voltage relative to ground (earth) and this voltage may be positive, negative or alternating. "Neutral" indicates that a conductor has a voltage, relative to earth, which is close to zero.

[edit] Ground (earth)

Modern cars have a "negative earth electrical system". This means that the negative pole of the battery is connected (grounded) to the vehicle's bodywork and the positive pole is "live". Older cars may have a "positive earth electrical system" in which the positive pole is grounded and the negative is "live". The concept of "positive earth" or "negative earth" is not relevant to AC circuits because the polarity of the poles alternates.

[edit] See also

• Anode
• Cathode
• Electric charge
• Polarity symbols

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