Electricity It’s How We Get Lights To Work

Intro  For theatre applications it isn’t necessary to have an extensive knowledge of how power is created or delivered  However, it is important to be familiar with a few terms, and one simple mathematical formula

Electrical Terms  Load: a device that converts electrical energy into another form of energy  Electricity flows along a wire, just like water flows from a faucet with force  Volts: the pressure that causes the flow  The level of pressure is established and maintained by the power company at the “household strength” level of 120 volts

Electrical Terms  The quantity of electricity that is used by a piece of equipment is its wattage, measured in watts  Like on light bulbs at home  The wattage indicates the quantity of electricity consumed AND gives a relative indication of brightness

Electrical Terms  Amperage: the rate or speed at which the power is used, rated in amps  Most electrical devices are rated by the maximum amps they can safely conduct  These values of pressure/volts, quantity/watts, and rate/amps are interrelated  They provide info about how much power is available to what and where

Circuits and AC/DC  Circuit: conductive path through which electricity flows  Circuit Breaker: device to protect circuit from an overload; magnetic device trips open to break the circuit  Direct Current: electron flow in 1 direction  Alternating Current: flow periodically changes polarity (directions), in US polarity changes every 1/120 th of a sec

A Series Circuit  All electricity flows through every element of circuit  If any lamps burn out, the circuit is broken, and the remaining lamps go out

A Parallel Circuit  Only a portion of electricity flows through each of the branches of circuit  If one burns out, electricity continues to flow in the rest of the circuit

A Combination Circuit  Any circuit that uses a switch to control a light is an example  A control device is used in series with the lamp load, and lamps are wired in parallel  Series = whole circuit control  Parallel = individual play

Just a little math  To determine how much power is needed to operate equipment or the capacity of equipment being used, apply the “West Virginia rule”  Watts = Volts x Amps  W = VA  Almost all lighting equipment uses 120 volts of current, so that value is usually known/constant

Practice   You want to plug up some Fresnels with 300 watt lamps. How many can you safely plug in using a 15 amp fuse?   Remember: it’s smart to load a little less than it can sustain. Safety!   W = VA (so….. 120V x 15a= 1800W)   1800W / 300W = 6 lamps   For the sake of safety, 5 lamps would be the correct answer. Get it?

More Practice  In order to sustain the flow of electricity, your cable needs to be rated to handle the amount of power flowing through it (in amps). You have five 250 watt lamps in your PAR cans. What does your cable need to be rated at to handle all these?  W=VA (so… 5 x 250W =1250W / 120V = amps)  Always round up to a whole number for amps, so the correct answer would be 11 amps.