Ohm’s law is the most important law of an electric circuit. It is the basis of almost all electrical calculations. It
allows you to calculate the current that runs through a cable (or a fuse) at different voltages. Knowing how
much current runs through a cable is essential knowledge to be able to choose the correct cable for your
But first some electricity basics are needed.
Electricity is movement of electrons in a material, called a conductor. This
movement creates an electric current. This current is measured in
“ampere” (amps for short) and the symbol is A.
The force required to make the electrons flow is called voltage (or
potential). It is measured in volt and the symbol is V (In Europe also
referred to as U).
When an electrical current passes through a material, it meets a certain
resistance. This resistance is measured in Ohm. The symbol is Ω.
Voltage, current and resistance are related to each other.
- When the resistance is low, many electrons move, and the current is high.
- When the resistance is higher, less electrons move, and the current is lower.
- When the resistance is very high, no electrons move at all, and the current has stopped.
You can say that the resistance of a conductor determines how much current runs through a material at a given voltage. This can be represented in a formula. The formula is called Ohm’s Law: