by Polymath

Created on: May 18, 2007   Last Updated: May 21, 2007

I will ignore three-phase and industrial wiring systems in this article, as only professionals (who already know this material) should ever deal with those, and concentrate on household wiring and appliances. Also, this will apply to ordinary, 120 vac (a.c. volts) wiring found in American households; different countries use different voltages and frequencies and standards, but some of this will apply to them as well.

First, a correction: "Positive, Negative and Ground" should read "Hot, Neutral and Ground" instead. For there to be 'positive' and 'negative', we would have to be talking about DC (direct current) systems. "Hot" is the line that carries the 120 vac (actually this value varies, and is usually closer to 115 volts). "Neutral" is the line that is held near zero volts (analogous to the 'return' wire in a DC system). "Ground" is just what it sounds like: the wire connected to actual earth ground.

Okay, so what does all that mean, and how does it help you? First understand that 'ground' is an absolute reference; lines connected to actual earth ground (that is, a metal rod driven into the earth) should be at exactly zero volts potential, always and undeniably. If a ground line reads some voltage above zero, that means that it has become disconnected or damaged somewhere between where you are reading and the outside ground connection. The ground line is included in household wiring basically as a safety feature: it gives stray energy somewhere safe to go.

'Neutral' should be equal or close in potential to ground. It is actually the 'center point' between two phases of electrical service coming to your house from the transformer on the electric pole; the lines from the pole are 240 vac apart, and in your circuit breaker box these supply two rows of breakers. One line supplies one row at 120 vac, the other line supplies the other row at 120 vac, with the neutral tapped betweeen them at (ideally) zero vac. The large loads in your home, like the air conditioner, that run on 240 vac power tap from both sides of the breaker box (straddle both buss bars). If you have ever heard an electrician comment on a home's electrical load being 'balanced', he is referring to whether the electrical current drawn from each 120vac line is equal or not. If they are unequal, then the 'center point' tends to shift away from zero volts, and thus so does the voltage on your 'neutral' lines.

'Hot' is exactly what it sounds like: it is the line with the 'juice' that supplies the energy

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