Calculators
Calculate parallel cables
Beyond a certain size a single conductor is no longer workable, since 240 mm² cannot sensibly be bent any more. Cables are then run in parallel. The arithmetic is simple, but the trap lies elsewhere. The current only divides evenly if the cables really are identical.
Result
- Total cross-section per line conductor
- —mm²
- Current per cable if evenly divided
- —A
- Current in the most heavily loaded cableThis cable governs, not the average.
- —A
- Margin on the most loaded cable
- —%
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
Parallel cables
Current sharing, total cross-section and the margin on the most loaded cable.
Discuss a projectWorked example
The default case the calculator starts with, worked through once. Change the values above and it recalculates immediately.
Inputs
- Number of parallel cables per line conductor
- 2
- Cross-section per cable
- 95 mm²
- Total current
- 400 A
- Current-carrying capacity per cable
- 230 A
- Assumed current imbalance
- 10 %
Result
- Total cross-section per line conductor
- 190 mm²
- Current per cable if evenly divided
- 200 A
- Current in the most heavily loaded cable
- 220 A
- Margin on the most loaded cable
- 4.35 %
Formula and standards
Formula
- A_total = n · A
- I per cable = I_total / n
- I_worst = I per cable · (1 + imbalance)
- Margin = (I_z − I_worst) / I_z
Assumptions and standards
- The calculation assumes equal cross-section and equal material for all parallel cables.
- The capacity per cable is entered and must already include grouping, since parallel cables lie close together and heat one another.
- The imbalance is an allowance, not a calculation. It grows with differences in length, installation method and position within the bundle.
Why does the current not divide evenly?
Because the impedances differ. A few metres of length difference, a different position in the bundle or one extra bend shifts the division. The cable with the lowest impedance takes the most current, and that one governs the heating.
What matters for the protection?
A common protective device only sees the total current. If one of the parallel cables fails, the others take over its share and become overloaded without the device operating. That is why execution matters here, meaning equal length, equal cross-section, equal installation method and no branches.
How many cables may I run in parallel?
There is no fixed technical limit, but in practice it becomes unwieldy beyond three or four. Check first whether busbar trunking is the better answer. It solves the symmetry question by construction.
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