Step 1 of 6 Electricity at home
Watts: how hungry is it?
Every appliance has a power rating in watts: how fast it uses energy. At the wall socket the push is about 230 volts, so the current an appliance draws is its power divided by 230. It's lesson 01's rule in another form: power = voltage × current.
This lesson explains how things work. It is not training for electrical work: never open plugs, sockets or appliances that are connected to the mains.
Plug appliances into the power meter. Find the one that draws close to 13 amps.
Why is a kettle's cable thicker than a lamp's?
Step 2 of 6 Electricity at home
The bill: kilowatt-hours
Your bill doesn't charge for watts. It charges for energy: power × time. The unit is the kilowatt-hour (kWh): 1,000 watts for one hour. A 2,000-watt heater for an hour uses 2 kWh; a 10-watt LED bulb takes 100 hours to use 1 kWh.
Choose an appliance and how long it runs. Use exactly 1 kWh.
Over a month, which uses more energy: an LED bulb left on day and night, or the kettle for 10 minutes a day?
Step 3 of 6 Electricity at home
Back and forth: AC
A battery pushes one way, so the charge drifts steadily round the loop: direct current (DC). The mains reverses its push many times a second: alternating current (AC). The charge in the wire just shuffles back and forth, yet energy still reaches the lamp, because the push itself travels along the wire.
Switch to the mains and watch the wave. How many full waves, back and forth, does the mains make in one second?
If the mains reverses 50 times a second, why don't the lights flicker?
Step 4 of 6 Electricity at home
Inside the cable
An appliance cable holds three wires. The live wire carries the push in. The neutral wire is the way back. The earth wire is a safety path that normally carries nothing at all. The three-pin plug also holds a small fuse.
Match each wire to its job. Tap a wire, then its name.
The fuse, and every switch, sits on the live wire. Why the live wire?
Step 5 of 6 Electricity at home
Too much on one socket
Things plugged into an extension lead sit side by side, so each gets the full push, like the side-by-side bulbs in lesson 01. Their currents add up in the lead. The 13-amp fuse in the lead's plug melts before the lead can overheat.
Run three appliances on the lead at once without blowing the fuse.
Plug the kettle and the heater into the lead together. What happens, and why?
Step 6 of 6 Electricity at home
When an appliance goes wrong
Suppose a loose live wire touches an appliance's metal case: the case is now at 230 volts. If the case is connected to the earth wire, a large current rushes to earth and the circuit breaker (or the plug's fuse) cuts the power. An RCD (residual current device) goes further. It compares the current in the live and neutral wires; if as little as 30 thousandths of an amp goes missing, through a person say, it cuts the power in a fraction of a second.
Never touch an appliance you think is faulty. Here a test probe stands in for a person.
This fuse box is an older one, with the RCD switched off. Keep the earth wire connected and make the fault. What cuts the power?
Now suppose the earth wire has come loose. Disconnect it, switch the RCD on, make the fault, and touch the case with the test probe.
Quiz Electricity at home
Check what you know
Six questions, 5 points each. One answer per question.
Done Electricity at home
Lesson complete
Now you can read your bill: watts tell you how hungry an appliance is, kilowatt-hours how much it ate. And you know what the earth wire, the fuse, the breaker and the RCD are each quietly doing to keep you safe.
MARIFA · Nothing you do here leaves this device.