Would also be nice, on the side, to know why the lights in the kitchen go dim when i turn the kettle on...?
Having looked at that tutorial, you need to know that every voltage source in the
real world, and every conductor of electricity, has resistance. The conductors that bring the mains into and around your house have a resistance.
When a current is forced to flow through a resistance, it develops a voltage drop across that resistance (see the page on Ohm's law). This voltage drop subtracts from the voltage available from the source, so you are left with less voltage.
So, let's say, for the sake of argument, that the substation at the end of your road is delivering a constant 230 Volts (it's not, but it's big enough that your kettle won't affect it too much). It's also an AC voltage, but for our purposes that doesn't matter.
There is a conductor between that substation and your house, a meter and a fuse where it enters your house, and then the circuits diverge at the consumer unit, with separate circuits (hopefully!) feeding your kettle socket and your kitchen light. There is therefore a resistance between you and the substation. A low one, nonetheless.
The more current your house draws, the more voltage is dropped in the resistance and therefore that constant 230 Volts is reduced by the time it gets to your house.
Your kettle is probably rated at around 2200 Watts. Power is related to volts and Amps as shown in the tutorial: P (Watts) = V (Volts) x I (Amps).
So, we know P = 2200 and V = 230.
Solving this equation for I we get I = P/V or about 9.6 Amps.
So, when you switch on your kettle, an extra 9.6 Amps flows through the resistance feeding your house. This results in an additional voltage drop meaning the voltage available to your kitchen light drops slightly too. The power equation above applies to your kitchen light too, so less power is consumed by it (due to the reduction in voltage) meaning less power is emitted as light and it dims.
Your household supply is probably rated for up to 100 Amps so an extra 9.6 shouldn't drop it by much (probably less than a Volt) but some lights are quite sensitive to voltage drops.
Watch the warning lights on the dash next time you start your car. They dim significantly when the starter motor is cranking the engine. Same principle but exaggerated a little. Starter motor takes a huge current from the battery (several hundred Amps), battery has a finite resistance, so its' voltage drops.
Kevin
Author
Topic: help with tools, electrical. (Read 4833 times)