Wiring and Protection
Bundled Cable Derating Calculator
Bundled Cable Derating provides a checkable estimate of bundled ampacity. It is intended for scenario comparison, not as automatic approval of a component or installation.
Run the Bundled Cable Derating scenario
Do not mix values recorded under different conditions.
Values this page needs
Record ambient temperature, bundling, insulation class, and termination conditions. Write down whether each entry is measured, rated, assumed, or calculated.
Confirm decimal placement whenever a source uses a different unit scale. For the companion base current calculation, open BJT Bias Calculator.
- Single-cable ampacity
- Default example: 35 A. Enter single-cable ampacity in A.
- Grouping factor
- Default example: 0.7. Enter grouping factor.
How the result is calculated
The displayed result follows ampacity = base × grouping factor. The entered quantities are Single-cable ampacity and Grouping factor.
The initial scenario returns 24.50 A. Re-enter field data before using the answer in a design or comparison.
Calculate bundled ampacity from single-cable ampacity and grouping factor. Conductor Temperature Derating Calculator covers the related derated ampacity step.
Compare two operating cases
Change Single-cable ampacity from 35 A to 42 A with the rest of the inputs held constant. The comparison runs from 24.50 A to 29.40 A.
This isolates one variable; a real system may change several at once.
What the number means
The calculated Bundled ampacity is meaningful only with its input conditions attached. Compare it with the selected conductor and protective-device ratings.
Label alternate cases rather than overwriting the baseline. Another relevant worksheet is Cable Tray Fill Calculator.
Practical limits
Spacing and the number of loaded conductors affect the factor.
A broader analysis may require code rules, manufacturer instructions, and field installation details. Use measurements, manufacturer data, or another calculation for effects that can change the decision.
Keep one-way and round-trip lengths clearly identified. If you also need conduit fill, continue with Electrical Conduit Fill Calculator.
Trace the result back to its source
Check the source of grouping factor before calculating. A credible result requires every field to describe the same physical condition and unit basis.
After calculating bundled ampacity, compare its magnitude with the applicable installation and equipment requirements. An independent order-of-magnitude check can reveal a misplaced decimal or unit prefix.
Document any effect handled outside this page, especially termination heating, installation method, ambient temperature, and grouping. That note prevents a later reader from assuming the simple equation covered it.
Common questions before using the result
Where is this bundled ampacity estimate simplified?
The result follows the displayed variables. Check fault duration, protective-device curves, and conductor thermal limits separately.
What explains a gap between calculated and observed bundled ampacity?
Differences can come from fault duration, protective-device curves, and conductor thermal limits, measurement uncertainty, or values taken under different conditions.
How should I compare two Bundled Cable Derating cases?
Keep unaffected entries fixed so the cause of the difference remains visible. Record ambient temperature, bundling, insulation class, and termination conditions.