Cable Ampacity Calculator: Comparing ampacity derating factors — Worked Scenario

What this scenario actually checks

Estimate the corrected ampacity of a known copper wire or cable, not a breaker or a load-selected wire size. Select the installation country and conductor size first: the Korean KEC/KS profile uses mm², while the US NEC 2023 reference uses AWG/kcmil. Review the installation method, insulation type, ambient temperature, grouped circuits and terminal limitations. The displayed current capacity changes with those conditions; for instance, 6 mm² XLPE copper in the Korean B2 reference at 40°C with two bunched circuits is reduced from the 44 A reference to about 32.03 A. Verify the adopted code edition, cable datasheet and protective-device coordination before applying a result to an installation.

This walkthrough focuses on comparing ampacity derating factors. It follows the published tool inputs, not a new formula or an automatically verified legal, financial, medical or engineering determination.

Start by preparing the right inputs

Choose the installation country independently of the display language. Korea KEC/KS and USA NEC 2023 are separate profiles; verify the locally adopted NEC edition. For sizing, enter load power, supply and breaker rating. For ampacity, select the conductor size. Review the visible defaults and expand installation conditions if they differ from your site.

Before copying the example, confirm that each entered unit, date, dimension and default matches your real task. Changing only a visible number without revisiting its assumptions can change what the answer means.

• Choose the installation country independently of the display language. Korea KEC/KS and USA NEC 2023 are separate profiles; verify the locally adopted NEC edition.
• For sizing, enter load power, supply and breaker rating. For ampacity, select the conductor size. Review the visible defaults and expand installation conditions if they differ from your site.
• Read the concise result, or expand Calculation details for correction factors and conditions. Voltage drop, protection coordination, equipment and manufacturer limits require separate verification.

Worked example with the calculator

Use the following input values: South Korea · 6 mm² Cu XLPE; 3 loaded; B2; 40°C; 2 bunched circuits.

The example output is 44 × 0.91 × 0.80 = 32.032 A. The 30°C single-circuit reference is reduced for warmer air and grouped circuits.

For comparison, the same tool also documents these inputs: South Korea · 6 mm² copper XLPE · three loaded conductors · B2 · 30°C · 1 circuit. Its result is Reference ampacity 44 A × 1.00 × 1.00 = 44 A. Use the same conductor and installation method as the 40°C two-circuit case, but retain the reference air temperature and a single circuit. This shows why actual grouping and ambient inputs matter.

What can change the answer

Read the concise result, or expand Calculation details for correction factors and conditions. Voltage drop, protection coordination, equipment and manufacturer limits require separate verification. Korea supports copper B2/C 1.5–300 mm². USA supports copper THHN/THWN-2 90°C, 14 AWG–500 kcmil under raceway/cable conditions, with a 60°C termination default, optional verified 75°C terminations, small-wire OCP caps and the selected 125% continuous-load allowance.

Is corrected conductor ampacity the same as a breaker rating? No. Corrected ampacity reflects conductor and installation assumptions. Breaker selection and protection coordination depend on the circuit and applicable requirements.

How do I calculate cable ampacity at 40°C with multiple grouped circuits? Choose the conductor and its installation method, read the reference ampacity, then apply the matching air-temperature and grouping factors. In the Korean B2 XLPE 6 mm² example, 44 A × 0.91 × 0.80 gives about 32.03 A; the factors differ for other methods and layouts.

Before using the result for a real decision

For comparing ampacity derating factors, check the original measurements and input units, and save the assumptions alongside any number you share.

Where legal rules, official allowances, equipment ratings or contractual conditions matter, consult their current authoritative documents. An illustrative estimate is not a substitute for that verification.

• Reproduce the example before changing inputs
• Check all units and assumptions, including any default values
• Verify official or manufacturer-specific requirements outside the calculator