How to choose the right extension cables, cable reels, and power distributors – to ensure power gets through
No matter how well-sized a power generator is, if there are cables that are too long, too thin, or wound up between the generator and the consumer, too little voltage will reach the end device – and equipment will experience problems. Typical symptoms include:
- Motors start with difficulty or shut down
- Compressors only "hum"
- Chargers, controls, or LED lighting flicker
- The generator seems "too weak" even though the kW rating is appropriate
The most common reason: voltage drop and heating in the cables. In this article, you will learn how to select cables, reels, and distributors so that your devices run reliably – and your power generator doesn't operate "below its value."
1) What is voltage drop – and why is it particularly critical with a generator?
Every cable has electrical resistance. When current flows, voltage drops along the line. The...
- longer the cable,
- higher the current,
- smaller the cross-section,
the greater the voltage drop.
In the public grid, this is often less noticeable because it is very "stable." A mobile power generator, on the other hand, reacts more sensitively to long cables and high currents – especially when consumers draw a lot of power for a short time at startup.
2) How much voltage drop is "still okay"?
As a practical guideline: You should try to keep the voltage drop low right up to the consumer. The less voltage is lost along the way, the better:
- Consumers function more stably (no flickering, no error messages)
- Motors start more reliably
- Cables and connectors remain cooler
In sensitive applications (electronics, chargers, LEDs, controls), it is particularly worthwhile to plan "with reserve."
3) Simple rules of thumb that really work
You don't have to do complicated calculations every time. These rules are sufficient in most cases:
- Double cable length → approximately double voltage drop
- Double current → approximately double voltage drop
- Larger cross-section → significantly less voltage drop
In short: Length and current drive the voltage drop – cross-section slows it down.
4) The classic: "50 m cable reel + Schuko + high load"
Why the generator often seems "too weak"
Many problems arise precisely in this combination:
- long cable
- high current
- Schuko plug system
- possibly motors/compressors with inrush current
- cable reel not fully unrolled
The result: Less voltage reaches the consumer. Motors start poorly, electronics malfunction, connectors get warm – and the impression is created that the power generator is too small.
Important: In many cases, the generator is not the problem, but the connection in between.
5) Correct cross-section selection: Practical recommendations
Here are proven recommendations for typical uses. If you are unsure, always remember: It's better to choose one size thicker.
230 V (Schuko) – typical applications
(Construction lights, hand tools, small pumps, chargers)
- up to approx. 20 m: often 1.5 mm² sufficient (with moderate load)
- 20–50 m: better 2.5 mm²
- from 50 m or with high continuous load / motor start: 2.5 mm² minimum, often 4 mm² advisable
400 V (CEE) – when power or distance increases
As soon as distances get longer or large consumers are running, 400 V is often the better solution in practice, because:
- currents are usually lower for the same power
- voltage drop and heating are thus reduced
- motors usually start more stably
If the generator and consumers are designed for it, it is worthwhile to switch to CEE/400 V for higher power and longer distances.
6) Cable reel: Always unroll completely (really!)
A partially wound cable reel can heat up significantly because:
- heat is poorly dissipated
- the cable core can get particularly hot
This is not only inefficient, but can lead to shutdowns (overheat protection) or, in the worst case, to damage.
Practical rule:
➡️ Unroll cable reels completely when under significant load.
Also useful:
- Do not place the reel in direct sunlight
- Do not cover it
- Do not operate in puddles or mud
7) Power distributors & connectors: Often the hidden weak point
It's not just the cable that matters – it's often the transitions and connections:
- Schuko plugs/couplers (contact quality)
- Multi-sockets (cheap strips are real sources of problems)
- Adapters from CEE to Schuko
- damaged couplers or "worn out" plugs
Poor contacts mean higher resistance – which leads to:
- additional voltage drop
- local heating
- in extreme cases, charred plugs
Recommendation: Use robust, high-quality components that are suitable for the environment (e.g., construction site/event).
8) Two practical examples
Example A: Lighting + small appliances (approx. 1–1.5 kW), 30 m distance
- Recommendation: 2.5 mm², unroll cable reel, stable connectors
- Goal: flicker-free lighting, reliable device function
Example B: Compressor or pump (motor load), 40–60 m distance
- Recommendation: if possible CEE/400 V, otherwise at least 2.5 mm², often 4 mm² advisable
- Background: Motor start is when voltage drop causes the most problems
9) Mini-checklist: The right cable in 60 seconds
- How far away is the consumer? (10 m, 25 m, 50 m, 100 m?)
- What load is connected? (Heater/ohmic, electronics, motor/compressor)
- Schuko or CEE? (for power & distance: prefer CEE)
- Choose appropriate cross-section (rather thicker than too thin)
- Unroll cable reel
- Distributor/plugs high-quality and undamaged
Conclusion: Many "generator problems" are cable problems
If the extension cable, cable reel, and power distributor are not suitable, power and voltage will not reach the consumer cleanly. However, those who carefully plan the cable route, cross-section, and plug system will get:
- more stable voltage
- fewer motor startup failures
- less heat at cables and plugs
- more reliable device function
And incidentally, the power generator can often be used more efficiently – because the energy reaches where it is needed.
If you have determined the right cable, you will surely find what you are looking for here:
https://sev-stromerzeuger.com/collections/kabel