Download Electricity Notes

Grueneich 2011
Theatre Tech
14-guage cable
500 W
2400 W
500 W
Dimmer
500 W
The cable can carry a maximum load of 1,800 watts. To determine the number of 500-watt lighting
instruments that can be carried by the cable, divide 1,800 by 500.
1,800 = 3.6
500
Theoretically, the cable can safely carry 3.6 instruments. Practically, it can safely carry three
instruments. Even though the dimmer can safely carry four instruments, the single cable connecting the
dimmer to the instruments can handle only the current flow generated by three 500-watt stage lighting
instruments
Electrical Curent
There are two types of electrical current, direct and alternating.
Direct Current
in direct current (DC) the electron flow is in one direction only. The flow of the
current is always from the negative terminal of a batter to its positive terminal.
All batteries are examples of direct current sources.
Alternating Current
The overwhelming majority of electrical power generated by power stations is
alternating current (AC). The electron flow in AC is the same as in DC with an
exception – the current flow periodically changes direction. In this United
States, alternating current changes polarity at the rate of sixty cycles per second
(60 Hz). This means that the electricity changes polarity (direction) every
1/120th of a second.
If the wires connected to the terminals of a battery were reversed, the lamp
would still emit light, but the current flow would have changed directions.
Alternating current works like this example, except that the direction of current
flow changes direction every 1/120th of a second