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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
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
Preventing Accidental Overload
Circuit breakers
small filaments (like light bulbs)
Burn out when too much current is drawn
bimetallic strip heats up when too much current is drawn
bends when heated which opens switch to prevent current flow
GFCI outlets and breakers
Complex circuitry that senses too much current almost
Opens circuit at outlet or breaker
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
1.0 A and higher – “cooked”
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