Prof. Dr. Thorsten Jungmann (last updated 2025-09-02)
1 What does it look like?
A cable reel (German: Kabeltrommel) consists of a round drum made of plastic or metal, onto which a flexible electric line is wound in several turns. On the front there are usually several socket-outlets, often with a cover, a switch or a thermal overload protector. A handle and a sturdy frame make it possible to carry the reel and to unwind it.
Cable reel 10 m
2 What can it do?
A cable reel extends the reach of electrical devices by providing an electric line in a flexible way. It allows several loads to be connected and offers a mobile energy supply.
3 How does it work?
The electric line is wound onto the drum in a spiral and connected to the socket-outlets. When the reel is connected to the mains, the mains voltage is available at the socket-outlets of the reel. Important: under high load the reel must be unwound completely, because otherwise the electric line heats up strongly (heat build-up).
4 What does it look like inside?
Inside there is the wound electric line, which is connected to the socket-outlets via terminals. A thermal overload protector is often built in, which interrupts the current supply in the event of overheating.
5 What role does it play in teaching?
Cable reels are a practical example for the topics of voltage drop, power loss and heating of electric lines. They illustrate the influencing quantities cross-section, length and winding state.
6 What role does it play in practice?
Cable reels are widely used on construction sites, in workshops, at events and in the home. They make a flexible power supply possible even over large distances. In practice, ingress protection ratings (IP44 or IP54 for outdoors), thermal protection and a suitable cable cross-section are decisive for safe use.
Symbols
- Letter code in schematics: X
Calculations
- Conductor length
- Conductor resistance
- Voltage drop