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Electrical Safety. Devices (TV, Refrigerator, etc) are rated for maximum power/voltage/etc. (They stop working if exceeded) Devices can be overpowered by accident by overloading outlets – draws too much current Example: plugging too many things into the same outlet
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Electrical Safety Devices (TV, Refrigerator, etc) are rated for maximum power/voltage/etc. (They stop working if exceeded) Devices can be overpowered by accident by • overloading outlets – draws too much current • Example: plugging too many things into the same outlet • Ground Fault (short circuit) – contact is made between live and ground conductors • Example: Working hair dryer in water – plumbing is connected to ground
Electrical Safety Preventing Accidental Overload • Fuses • small filaments (like light bulbs) • Burn out when too much current is drawn • Circuit breakers • bimetallic strip heats up when too much current is drawn • bends when heated which opens switch to prevent current flow • http://electronics.howstuffworks.com/circuit-breaker2.htm • GFCI outlets and breakers • Complex circuitry that senses too much current almost instantly • Opens circuit at outlet or breaker • http://home.howstuffworks.com/question117.htm
Current Danger 0.00l A and higher – feel shock 0.01A and higher – unable to release 0.02 A and higher – paralyzes respiratory muscles (you can’t breath) 0.1 A and higher – ventricular fibrillation (erratic heartbeat) 1.0 A and higher – “cooked”
Why don’t high Voltages always hurt us? Skin has very high resistance – approximately 100,000 Ω So, V = IR 10 V = I (100,000 Ω) I = 0.0001 A Remember! You can’t have a current without a voltage