Short Circuits and Electrical Safety

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

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

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

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

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

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