# Cable size depends on current, but also on length! > Why cable size depends on current but also on length: resistance, heating and voltage drop, explained simply. Source: https://www.darkside-energy.com/en/did-you-know/cable-size/ · Dark Side Energy · Updated: 2026-10-06 8 May 2017 · 1 min read · Updated 6 October 2026 - A cable is a very good conductor, but it is also a resistance. - The longer it is, the more it heats up and the greater the voltage drop. - Cable size is therefore chosen according to the current and according to the length. The size of electrical cables is very (too) often overlooked. In simple terms, voltage (in volts) pushes current (in amperes), held back by resistance (in ohms). Plenty of calculations explain this, but the aim of these articles is to help you understand the basics of our trade in a simple way. An electrical cable is made of copper or aluminium. These materials are very good conductors, but they are also resistances (small, but present). The length of a cable increases its heating and causes a **voltage drop**. Many devices have a fairly narrow acceptable voltage range: often 220 to 250 V. If a device receives less, it may not work properly, or may even fail. Choosing the cable size is therefore important when running long lengths. There are many charts that let you choose easily, and our calculator does it for you. Calculate the voltage drop on your line: cable size, length, current, single-phase or three-phase. [Open the electrical calculator](https://www.darkside-energy.com/en/electrical-calculator/#chute-de-tension) [What is a Twin zero-interruption generator set?](https://www.darkside-energy.com/en/did-you-know/twin-generators/) [Why does it “trip”?](https://www.darkside-energy.com/en/did-you-know/why-it-trips/) ## A project? Let's talk power. Venue, dates, known requirements: tell us about your event and we will get back to you quickly. [Request a quote](https://www.darkside-energy.com/en/contact/) [contact@darkside-energy.com](mailto:contact@darkside-energy.com)