Current-Carrying Capacity is usually heard when you need to wire a house or install appliances when you need to. But what does it mean when it comes to creating an electrical plan or using the right wire for electrical motors? When we use electrical devices, it’s important to know how much electricity (called current) a cable can safely carry. A simple rule to remember is: the thicker the cable, the more electricity it can carry. Besides the thickness (called cross-section) of the cable, other things like how hot it is around the cable and what the cable is made of also matter.

This article will help you understand what “Current-Carrying Capacity” means and how to figure out how much electricity a cable can safely handle.

What is Current-Carrying Capacity?

Current-Carrying Capacity means the most electricity a cable can carry without getting too hot. If the cable gets too hot, it can melt or break. There are rules, like the VDE and IEC standards, that help people figure this out safely. These rules also say that we have to look at the temperature inside the wire and not just the outside. If the inside gets too hot, it can damage the outside of the cable too.

Remember: Bigger cables can carry more electricity.

How to calculate it

To calculate how much electricity a cable can carry, we need to know a few things:

We need to know the cable size, the length of the cable, the type of material (copper or aluminium), the voltage, and how well the material carries electricity. For example, here is a formula used by engineers:

This can be changed to find current like this:

Here’s what the letters mean:

A is the size of the cable in square millimetres. L is how long the cable is. I is the amount of current in amps. cos φ shows how efficient the electricity is (usually between 0.9 and 1). y is how well the material conducts electricity (56 for copper, 37 for aluminium). Vd is the voltage drop. V is the voltage of the system. 1.732 is just a number we use when we work with three wires (called three-phase).

There’s also another formula for a different kind of electricity:

And to get the current from that:

What affects how much electricity a cable can carry?

The size of the cable is important, but there are other things too:

If it’s hot outside, the cable might not be able to cool down. Cables need to stay cooler than their surroundings to work well. If lots of wires are close together or rolled up, they can get hotter faster. The material around the wire, like plastic or rubber, also affects how hot it gets.

Different cables carry different amounts

Depending on how a cable is built and where it’s used, the amount of current it can carry changes. For example, if a copper cable is used in a wall and has two wires carrying electricity, then, A 1.5 mm² cable should carry no more than 19.5 amps. A 2.5 mm² cable can carry up to 27 amps.

Underground cables

Underground cables are used for things like powering garden lights or machines. These cables are buried in the ground and don’t have air around them to cool off like regular wires do. Because the ground doesn’t cool the cables very well, the wires can get hot more quickly. If they get too hot, they can break or melt. So we must limit how much electricity goes through them or use bigger cables to keep them cooler. These underground cables are often used to carry electricity around neighborhoods or buildings at lower or medium voltages.