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Electricity Basics

Electricity is the flow of electrons from one place to another.

Resistance measures how easily it flows. Ohms is the unit of measurement for resistance in a circuit.

Voltage is push or force of the electricity.

Amperage is the frequency, or rate of flow over time.

Matter can be broken down into:

    - Conductors: electrons flow easily; there is low resistance.

     - Semi-conductors: electron can be made to flow under certain circumstances. Resistance varies or is controlled.

    - Insulator: electrons do not flow easily; there is very high resistance.

Ohm's Law: R = E / I

R = Resistance (ohms)

E = Electro-motive Force (volts)

I = Intensity of Current (amps)

Ohms = Volts/Amps

Wattage is the current, or total power.

Voltage (V) x Amps (A) = Watts (W)

West Virginia Rule -      W=VA


Most Dimmers in theater (all in BCPA):      

120V x 20A = 2400W

Pay attention to the wattage of the fixture and lamp you are using before you decide

how many lights to tie together on the same circuit.

LAMP WATTAGE (On a 2400 Watt Circuit)                                Number Of Lights Per Circuit

550                                                                                                                         4

750                                                                                                                         3

1200                                                                                                                       2

1500                                                                                                                       1

Series Circuits

A Circuit is a controlled route for electricity to flow, from a source, through an output, back to the source.

Circuits can be series or parallel, or a combination of the two.
In a series circuit, each output has to complete the circuit. If one fails, the entire circuit goes down. The common example is christmas tree lights.


Parallel Circuits

In a parallel circuit, each output is independent and one failure does not break the circuit.


3 Phase Power Distribution


There are generally two forms in which electricity can be distributed, Direct Current and Alternating Current.

Direct Current means on and off, one terminal is positively charged, the other negatively charged, and electricity flows from one to the other. However, while it is simple to make and control, DC does not travel well over long distances.

Alternating Current also has a positive and a negative terminal, but the power flow alternates continuously. AC can travel well over long distances, and so it the choice for power distribution lines.

High voltage power is supplied as 3-phase or WYE service. This means 3 hot "legs" of power at 120V each, plus an electrical neutral and a ground. Two legs put together make up 208V due to sine wave redundancy.

The neutral wire is often confused with ground wire, but in reality, they serve two distinct purposes. Neutral wires (always white connectors) carry currents back to power source to better control and regulate voltage. Its overall purpose is to serve as a path to return energy. Ground wires (always green connectors) are electrical paths designed to carry fault currents when a power abnormality occurs. They don't carry currents -” their purpose is to provide operator safety. The Hot connectors can be black, blue, red, or other colors. 

When a system has a current supplied to it, i.e. the bull switch is flipped ON,

the system is HOT.

The important thing to remember is that if anything is plugged in, it should be the ground. The next most important is neutral.

Therefore when tying in feeder cable WHETHER IT IS HOT OR NOT, the order is:



  3. HOT A

  4. HOT B

  5. HOT C

The order of the HOT's is not entirely important, but following the color code makes troubleshooting problems much easier.

When untying power at the end of the day, reverse the order. Remember, if anything is plugged in, GROUND should be plugged in.

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