Download Notes on Electricity

Notes on Electricity
NOTES ON ELECTRICITY
The best way to keep from burning yourself and your equipment is to avoid overloading your electric circuits. The best way to avoid overloads
(barring abstinence) is to know what your power consumption is, and to know the limitations of your equipment. The simplest way to figure your
power consumption is with this variation on Ohm's Law: Power (Watts) is equal to Force (Volts) multiplied by Current (Amperes). The formula
looks like this:
W = VA
You can remember it because it's the initials for West Virginia, which is ironic since West Virginia doesn't have electricity yet. To figure out how
much current (Amps) you're pulling, divide the Wattage by the Voltage, like this:
W/V = A.
The easy and quick way to do this is to estimate. Figure your line voltage to be 100 Volts instead of 117 or 125 or whatever it actually is. Then it's
easy to determine how much current you need for a given instrument, just divide by 100. This method has the added advantage of overestimating
your current draw, erring on the side of caution, as it were.
Some practical examples:
Teenie-Weenie = 600W, so 600W/100V = 6 Amps. 1K Fresnel = 1000W(duh!), so 1000W/100V = 10 Amps. Teenie-Weenie kit = 600W x 3 =
1800W/100V = 18 Amps.
This formula works for any electrical device as long as you know the power output in Watts, so you can apply it to your toaster or television set.
You can manipulate the formula to find other values. If you know the current pulled by an electric motor, for example, you can figure the Wattage.
For those who are interested, you can then figure out the horsepower output from your blender. Hint: one horsepower equals 746 Watts. In a
perfect world, all the wires, connectors and devices in a given circuit would have the same rating, and the circuit breaker would be of the correct
value to protect that circuit. Unfortunately that's not always the case. A standard household Edison circuit is generally rated for 15 or 20 Amps.
When in doubt, always assume the lower rating. Even if the circuit is rated for 20 Amps, the outlets on your extension cords are usually only
capable of handling 15. This means it's possible for you to pull up to 20 Amps through your 15 Amp extension cord, and the cord will melt or burn
before the circuit breaker shuts off the current. This is what we call an electrical overload, which is a really nifty way to start fires and create a
shock hazard! The trick, then, is to shoot outside in the sun, and not use electric lights at all. If you must use lights, avoid hooking too many
devices up to one circuit. Pretty simple, eh? It is worth noting that a single light can be "too many devices" for a circuit that can't handle the needs
of that light.
Extension cord and outlet guidelines: "14/3" written on a cable tells us that the wires inside are 14 gauge, and that there are 3 of them. 12/3
means, you guessed it, 12 gauge. Something that says 14/2 or 10/2 has only 2 conductors (i.e. no ground wire) inside, and should not be used as
an extension cord. By the way, the lower the gauge number, the bigger the wire, the more power it can handle. Ten gauge and 12 gauge are
heavy duty. You must choose your extension cords with your power consumption in mind. Assuming you've done your math, you can use the
information below to help choose extension cords that are capable of safely handling the load you're planning to put on them. 14 gauge stranded
copper wire is rated for 12-15 Amps. 12 gauge stranded copper wire is rated for 18-20 Amps. 10 gauge stranded copper wire is rated for 25-30
Amps. A standard Edison plug (3-prong household outlet) is usually rated for 15 Amps. All electrical conductors and connectors should have their
current rating listed on them somewhere, but sometimes they don't. You must never assume that using two different outlets in a room means
you're using two different circuits. Usually the outlets in a room are on the same circuit, and very often that circuit extends to ceiling fixtures or
outlets in other rooms as well. So don't think you're safe because you plugged three 1K's into three different plugs in someone's living room! If you
don't know enough about house wiring to determine what circuits you're using, find someone who does, or use fewer or smaller lights to avoid
possible overloads. Better yet, shoot outside! When you start electrical fires, not only could someone be hurt and equipment or property be
damaged, but you end up looking really stupid. If you have any doubt about what you're doing, please ask before you see smoke!
Types of Electrical Connectors
The following chart which was downloaded 10/29/2010 from this link (PDF) outlines the various straight-blade and twist-lock connectors used in
the US. Note that a 5-15 connector is also often called an Edison plug.