Parallel Cable Sets Calculator
Number of parallel cables needed for a design current after grouping derating. With the formula, a worked example and typical values.
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Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
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About this calculator
This page calculates cables per phase and derated current of one cable from design current, rated current of one cable and grouping and other derating factor. Change any value or its unit and the result updates. The steps below show the working for the default values, so you can check each line against your own method.
Limits of this calculator
Parallel cables must have equal length, size and route conditions or the current will not share. Keep each set a similar distance from the others.
Cross-check: 52 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review.
Verification status: Indicative
Indicative. Estimation only; further engineering checks are required. Basis: Assumes equal sharing between identical cables.
What this calculator checks
- Number of equal cable sets needed so that each carries no more than Iz × k.
What remains unverified
- Whether the sets really share current equally (length, route, spacing, termination).
- Voltage drop, grouping and short-circuit withstand of the sets.
Verification register entry
| Calculation author | Rahul Sharma (author) |
|---|---|
| Technical review | No independent technical review has been carried out |
| Individual professional approval | Not recorded |
| Formula reference | not recorded |
| Standard and edition | IEC 60364-5-52, 2009 + A1:2024, consolidated Ed 3.1 |
| Standard review state | Public-scope screened; licensed clause review still pending |
| Scope-screening note | Parallel conductor installation and current-carrying capacity are relevant. The calculator estimates set count from user-supplied ampacity and factors; it does not verify equal current sharing, cable arrangement, terminals or derating tables. |
| Cross-check test cases | 52 reference vectors (tests/reference_vectors.json) |
| Review date | not recorded |
| Next review date | not recorded |
| Status | Indicative |
Needed before this calculator can be marked Verified: reviewer name, qualification and review date; licensed clause-by-clause standard review; exact formula reference; formula source (textbook or standard); next review date.
Formula
Worked example
| Input | Value |
|---|---|
| Design current | 1,200 A |
| Rated current of one cable | 400 A |
| Grouping and other derating factor | 0.8 |
- Derated current per cable = 400 × 0.8 = 320 A
- n = 1,200 / 320 = 3.75, rounded up to 4
Assumptions
- Equal cables of the same length and type
- Current shares equally
Parallel cables must have equal length, size and route conditions or the current will not share. Keep each set a similar distance from the others.
Inputs and results
| Input | Unit | Allowed or shown | Note |
|---|---|---|---|
| Design current | A | greater than 0 A | |
| Rated current of one cable | A | greater than 0 A | From the data sheet for the installation method |
| Grouping and other derating factor | (number) | 0.1 or more, up to 1 |
| Result | Unit | Allowed or shown | Note |
|---|---|---|---|
| Cables per phase | (number) | Shown to 0 decimal places | |
| Derated current of one cable | A | Shown to 1 decimal place |
How it is calculated
Each input is converted to the base unit of its quantity, the formula above is applied in the order shown in the worked example, and each result is shown in the unit you choose. Results are held at full precision and rounded only for display, except where a step selects a standard size, as the worked example shows. A value outside its allowed range is refused with a message instead of giving a result.
How the result changes with design current
| Design current (A) | Cables per phase | Derated current of one cable (A) |
|---|---|---|
| 120 | 1 | 320 |
| 300 | 1 | 320 |
| 600 | 2 | 320 |
| 1,200 | 4 | 320 |
| 2,400 | 8 | 320 |
| 4,800 | 15 | 320 |
| 12,000 | 38 | 320 |
Other inputs are the same as in the worked example above.
Standards and further reading
- IEC 60364-5-52 (selection and erection of wiring systems, current-carrying capacity)
- IEC 60364-4-43 (protection against overcurrent, short-circuit withstand k factors)
- IEC 60228 (conductor sizes)
- IEC 60287 (calculation of cable current rating)
Ampacity and grouping factors come from your cable data sheet or your licensed copy of the standard; see STANDARDS.md for the method constants Elecmetric does use. These are named as background reading. Elecmetric does not embed clause text or rating tables, and the reviewer record for this calculator is separate from this list.
Frequently asked questions
What do I need to enter?
Enter design current, rated current of one cable and grouping and other derating factor. Change the unit of a value with its selector and the result stays the same.
What does this calculator assume?
Equal cables of the same length and type. Current shares equally.
Which calculators should I use next?
Common next steps are Cable Derating and Ampacity and Cable Short-Circuit Withstand. The related links at the bottom of this page open them.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. 52 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review. Check design values against the standard and the equipment data you work to.
Formula guides and reference
Longer explanations with worked examples and tables, written for the same topic.
- Cable Size Formulas: Current and Short-Circuit: Cable sizing formulas for current capacity with correction factors, conductor resistance and temperature
- Conductor Resistance Formulas and Temperature: Conductor resistance formulas: resistance from length, area and resistivity, correction for temperature
More Cable Engineering calculatorsAll engineering calculatorsParallel Cable Sets in Elecmetric