Electrical Theory and Practice

1. What is the standard voltage in the United States?

120 volts.

2. What is the relationship between volts, amps, and watts?

Definitions:

• Voltage is the force (or potential force) behind the electrons as they move through the circuit,
• amperage is the amount of electrical current flowing in the circuit, and
• wattage is the amount of power, or work, performed.

Wattage is equal to voltage times amperage, or as a mathematical formula: W = V * A -- the West Virginia Formula.

Amperage is equal to wattage divided by voltage, as a mathematical formula: A = W / V or in North America, A = W / 120.

3. What is the function of the circuit breaker (or fuse)?

The circuit breaker (or fuse) protects the theatre's wiring from an electrical overload which could cause a fire.

4. What should determine the rating of the circuit breaker?

The capacity of the breaker (or fuse) is determined by size of the theatre's wiring. For example, a #12 AWG wire, which according to the National Electrical Code can safely carry 20 amps, should be fused at 20 amps.

5. What is the capacity, in amps, of #12/3 cable?

20 amps, 2400 watts @ 120 volts

    Of #14/3 cable?

15 amps, 1800 watts @ 120 volts

    Of #16/3 cable?

13 amps, 1560 watts @ 120 volts

    Of #18/3 cable?

10 amps, 1200 watts @ 120 volts

6. Define: #12/3 SO

• #12-- 12 gauge wire, capacity = 20 amps
• 3-- Three conductors: Hot, Neutral (or Common) and Ground
• SO-- Two or more stranded conductors with a serving of cotton between the copper and the insulation. Jute fibers, or other fillers, are twisted together with the conductors to make a round cord. The outer jacket is of high quality oil resistent rubber. A 50'-- #12/3 SO cable with 20amp twist lock connectors costs $ 62.75 from Stagetechnology.

7. How many 750 watt lamps can be ganged on one #14/3 cable?

Two lights.
#14 gauge cable has a rated capacity of 15 amps or 1800 watts (at 120 volts). 1800 watts divided by 750 watts per light = 2.4 instruments. Obviously you can not have a .4 lamp.

8. How many 1000 watt lamps can be ganged together on one #12/3 cable?

Also two.

9. What type of connectors are commonly used in the theatre?

1. 20amp Stage Pin (Cost: $ 10.00 / pair in the 2004 StageTechnology catalogue)
2. 20amp Twistlock (Cost: $ 12.75 / pair)
3. 15amp U-Ground Parallel Blade (also known as a Household or Edison plug) (Cost: $ 9.25 / pair)

   See Figure 14.57 on page 368.

10. Which type of connector do we use in Johnson Center?

Twenty amp twistlock. Broadway and most commercial road houses use pin connectors, college and university theatres generally use either pin or twistlock connectors and many community theatres use parallel blade (household) plugs.

11. What is the difference between the line connector and the load connector?

The load connector is the plug on the light and the line connector is the outlet in the wall pocket, connector strip or on the back of the dimmer pack.

    What are their more common names?

The load connector is the male plug and the line connector is the female plug.

12. According to traditional practice, what should be the color of the insulation of the hot wire,

Black

    The neutral wire, and

White

    The ground wire?

Green

13. What is the difference between a cable, and a jumper?

A cable is generally long, at least 50 feet, and typically runs between the light and the dimmer rack. A jumper is short, 10 to 50 feet and is used with a two-fer to gang two instruments together.

14. What is a two-fer?

A two-fer is a Y connector with one male plug and two female plugs. It is used with a jumper to gang two lamps together on the same cable. See Figure 14.59 on page 369.