Tuesday, July 8, 2014

Basic AC Electricity

Chaplain Tim has been discussing DC power -- and good on him, because it is really out of my wheelhouse.  As a commercial electrician, though, AC power is right up my alley.

The good chaplain laid out a pretty good overview of what electricity is, so I'll start with the practical differences between DC power and AC power:
  • AC power mainly comes out of your walls and ceiling, into outlets, lights, and other appliances.  
  • DC power is more commonly used for battery-operated devices.  There aren't many DC devices that are hard-wired into their power supply.

Two Basic Types

There are two basic types of AC power: Single phase and Three phase.  Three phase is almost exclusively used in commercial and industrial facilities, so we won't cover it much here.  If there is interest, I can do a piece on it as well, but most folks will never interact with it.

Single phase AC is what is present in homes in the USA.  Outlets and lighting use roughly 120 volts (+/- 5% is acceptable, to account for a whole host of variables in the system).  Heavy-draw appliances, namely clothes dryers, electric ovens, and some furnaces and water heating systems, pull 240 volts using special circuit breakers and a double circuit.  Some heavy-load tools also use 240 volts, but they're rather uncommon for homeowners.

When dealing with AC circuits, there are a couple standards for wire in single-phase systems:
  • As with DC power, green is always ground.
  • White or gray is always your neutral wire.
  • Black and red are the most common "hot" wire colors, but sometimes other colors are used.  Assume that any non-green, -white, or -gray wire is hot, as a matter of precaution.  However, during normal operation, current will be present on both the hot and neutral wires, so touching either on a live circuit can result in an unpleasant shock, or much worse.

Fuses and Circuit Breakers

In your home, there will be some manner of protective devices for all of your electrical circuits. In older homes, these devices may be fuses. In newer homes, or older homes that have had electrical update work done, they'll likely be resettable circuit breakers.
A common household fuse.

A selection of resettable circuit breakers.

Now that you know some of the parts and pieces of your electrical system, next week we'll talk about what to do when things don't work right.


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