1. Short Circuits and Electrical Safety

2. Short Circuits
Short Circuit – an accidental low-resistance connection between two points on a circuit, causing excess electron flow
Can be dangerous
Example:
Knocked down telephone line
REVIEW Draw a circuit diagram:
series: with a battery, wires, and one light bulb
Parallel: with a battery, wires, and two light bulbs
What happens to the voltage in a series circuit when more loads are added
Whar happens to the current in a parrelllel circuit when more loads are added
How do combinations curcuits help prevent problems in circuits at home?
Sometimes a wires insulation breaks down or another problem develops that aloows electrons to flow through a device along a different path then the one intended
Cause electrical devices not to work and can be dangerous
Can quickly become hot and start a fire
Example:
From a storm
If you come in contact with the wire the electricity will take the path through your body to the ground and can kill you
You are safe inside the car
Jump from the car, so there is no path for electrons to flow through him
Technicians can purposely short out a curcuit by intentionally putting a wire across a load in a parallel circuit
The low resistance causes the current to flow through it rather then the high resistance devices
He can work on the devices with out intruuupting the rest of the current

3. Electrical Safety All electrical appliances present risk
Some devices retain a charge even when they are unplugged
Always handle with care and observe all safety precautions
Disconnect the plug before handeling the appliance.
This is why many devices have DO NOT OPEN wanrnings on them
Always contact a repair man when these devices break down

4. Three Prong Plug
The third prong connects the device to the ground wire of the building
In case of a short circuit
Ground wire sends any unwate current flow directly to the ground
One prong carries the current to the load
The other returns the currnet

5. Fuses and Circuit Breakers
Fuse – a safety device in a electrical circuit that has a metallic conductor with a low melting point compared to the circuit wires
Fuses are used in houses to act as a first line of defence if something goes wrong
If current gets too high the metal in the fuse will melt and current flow stops
This prevents further problems; damage to electrical components or fire)
A blown fuse must be physically replaced as it can work only once
The spring mechanism turns off the flow of electricity
Once the breaker cools it can be reset
Older homes and apartment building tend to have fuse panals where modern homes have circuit breakets

6. Circuit Breakers
Circuit Breaker – does the same job as a fuse except the wire inside does not melt; it heats up and bends to trigger a spring mechanism
Once it is cooled it can be reset
Modern homes

7. Ground Fault Circuit Interrupter (GFCI)
A device that detects change in current and opens the current; stopping flow
Example:
If an appliace happens to get wet while you are handleing it and some current starts to flow through the watre the GFCI opens and circuit so there is less chance you can be injured
DON’T HADE ELECTRICAL APPLIANCES AROUND WATER
Eectrical safety poster