Calculators
Calculate power loss in a cable
Every cable consumes part of what it carries. Over short runs that is irrelevant. Over long routes at high current it becomes a figure with two faces, namely running cost over the lifetime and heat that has to go somewhere.
Result
- Power loss
- —W
- Energy lost per year
- —kWh
- Cost per year
- —€
- Heat per metreDecides whether the cable becomes a problem in a duct or an enclosure.
- —W/m
Please fill all fields with valid numbers.
A guide, not a design to standard. We give no warranty for the correctness of the results. The applicable standards and case-by-case verification govern.
The grey values are an example. Simply enter your own.
Matching services
Calculating is the easy part.
A formula gives you a number. Designing a plant also demands installation method, grouping, discrimination, the standards in force and a look at the installed base. That is what we take on.
Method and questions
Cable losses
The heat and the running cost that stay in the cable itself.
Discuss a projectWorked example
The default case the calculator starts with, worked through once. Change the values above and it recalculates immediately.
Inputs
- System
- Three-phase (3~)
- Operating current
- 32 A
- One-way cable length
- 45 m
- Conductor cross-section
- 6 mm²
- Conductor material
- Copper (κ = 56 m/Ω·mm²)
- Conductor temperature
- 70 °C
- Operating hours per year
- 4,000 h
- Electricity price
- 25 ct/kWh
Result
- Power loss
- 492 W
- Energy lost per year
- 1,969 kWh
- Cost per year
- 492 €
- Heat per metre
- 10.9 W/m
Formula and standards
Formula
- Three-phase P_v = 3 · I² · R
- Single-phase and DC P_v = 2 · I² · R
- R = L / (κ · A) · [1 + α · (ϑ − 20 °C)]
- W = P_v · t / 1000
Assumptions and standards
- The calculation covers the resistance of the live conductors, not the protective conductor.
- For balanced three-phase load no current flows in the neutral. Three line conductors are counted.
- Harmonics are not included. A strong third-harmonic content loads the neutral in addition.
Is a larger cross-section worth it for the losses alone?
On long, heavily loaded routes, often yes. Losses fall in inverse proportion to cross-section. One size up saves roughly a third. Weigh the saving over the planned lifetime against the extra cost of cable and installation.
Why is heat per metre shown?
Because it decides whether the cable causes trouble elsewhere. In an open tray it hardly matters. In a filled duct, in thermal insulation or inside an enclosure it is part of the heat balance.
Does this hold at partial load?
It holds for the current you enter. Because losses go with the square of the current, you must not use an average when the load varies strongly, as the result would be too low. Calculate section by section instead.
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