Electricity what doesn’t kill you…. really, really hurts.

Electrical Circuits

Power Hot + Neutral - Ground

Lighting Rods People who live in areas with lots of lightning install lightning rods to protect their homes. A lightning rod is a metal spire on the highest point of a house connected by a metal wire to a metal rod buried in the ground. The lightning rod provides a path of least resistance to the ground, and the lightning will hit it instead of the wood house because electricity wants to go to the ground and will take the path of least resistance to get there.

The Path of Least Resistance O O X X a. b.

ConductorCombustibleInsulator What allows energy such as heat or electricity to pass through easily? What might light on FIRE if enough energy tried to pass through? What doesn’t allow energy to pass through? Path of least resistance More resistance Even MORE resistance

What are people made out of? WATER In fact, 60% of a person is water. The rest is meat, leather, and fiber. People are more conductive than combustible, but less conductive than metal.

Electricity will always take the path of least resistance. If both routes are conductive, it will take the shortest route. If one route is LESS conductive, it will take the MORE conductive route. Since people are less conductive than metal, a metal route to the ground will keep YOU from being the path of least resistance.

DO NOT BE THE PATH OF LEAST RESISTANCE. How can you avoid being the path of least resistance? Use properly grounded circuits Unplug equipment before making adjustments or repairs Do not circumvent breakers or fuses with pennies, paperclips, etc. Wear rubber-soled shoes Never work in wet or damp environments, or if you are damp or wet Avoid working with live electricity

What is the ground circuit? A circuit that protects you by providing a path of least resistance. In a building, this typically looks like a wire that connects all the 3rd prongs of all the outlets to a rod buried in the ground, much like a lightning rod.

Defeating the Ground Circuit Never remove a third prong or use an adapter improperly- this DEFEATS THE GROUND CIRCUIT.

Why do my lights turn off when I use the microwave while my sister is using the blow dryer? Because the circuit breakers in your house are designed to shut off the power to a circuit if an unsafe amount of power is being used. Your house’s electrical system is broken up into circuits- a new home has many, but an old home may only have a few. That’s because before the 60’s, there were relatively few electrical devices in the home.

Why is too much power on a circuit unsafe? Wire is made out of metal. While metal is conductive, it is not PERFECTLY conductive. Some percentage of the electricity will become lost as heat; this is called resistance. The longer the path of wire, the more resistance it will have. The thicker the wire, the more electricity it can carry. If the amount of electricity that passes through the wire exceeds the safe limit for the thickness of that wire, the extra electricity will be lost as heat because of resistance. If the resistance is too high, there might be enough heat to start a fire.

Fires From Frayed Cords, Over-Loaded Circuts, and Over-Loaded Cords

Circuit Breakers and Fuses Wire in your house is rated to carry a certain amount of power safely. When the draw- the amount of power used by an electric device- exceeds that rating, the breaker shuts off the power to prevent a fire. People draw a LOT of power when they are being electrocuted; breakers and fuses save lives!

How should I pick a cable or extension cord? Choose the shortest cable that will do the job. As length increases, resistance increases. As resistance increases, heat increases. If there’s enough heat, there will be a fire. Choose a cable that can handle all the power a circuit can put out- otherwise, someone might plug in an extra item and overload the cable- and possibly start a fire.

The Power Formula Watts = Volts x Amps W=V x A Also called “west equals Virginia” In the USA, residential power is ALWAYS about 110 Volts. Theatrical dimmers are usually 20 Amps, Residential circuit breakers are usually 15 Amps. How can you tell how much power things draw?

Using the Formula W = V x A W = 110 x 15 W = 1650 If we’re in a house in the USA, we can assume that V= 110, and A= 15.

Residential light bulb: watts Average Stage Lamp: watts Blow Dryer: 1500 watts Vaccum: watts Microwave: 1000 watts Xbox: 160 watts CRT TV (regular): watts Flat Screen TV: watts Phone Charger: 10 watts How much is 1650 watts?

How many amps does it take to kill a person? Amps Which is the same thing as 65 Millivolts. It’s the VOLTS that JOLTS, but the MILs that KILLS.

How do people die from electrocution? If current passes through the heart, it will disrupt the natural electrical signals from your brain that make your heart beat. If your heart stops, you will die. Where is your heart? If you are the path of least resistance, will the electricity pass through your heart?

Right hand to left hand Right hand to right foot Right hand to left foot Left hand to right foot Left hand to left foot What route avoids your heart? Always use your right hand when working with live power- and keep your left hand in your pocket!

Bob’s Story

Bob

P X

Light and Heat Most lightbulbs work by heating up the filament (the little wire inside) until it GLOWS. That’s why they’re called incandescent bulbs. The more power the lightbulb uses, the hotter it gets. Metal conducts ENERGY- electricity AND heat. Metal near a lightbulb will get very, very hot. Ever tried to cook a hot dog by putting it on a fork over the stove? It’s like that. How can you protect yourself?

Safety Cable Safety Cables keep lights, speakers, projectors, lighting accessories, and other heavy objects from falling on the actors or audience in an emergency.

Safety Lanyard Safety lanyards keep tools from falling on people below if you drop them.