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Adiabatic / CPC Check

BS 7671 protective-conductor sizing from first principles using the adiabatic equation k²S² ≥ I²t. You supply the k value from BS 7671 Table 54.3 or 54.4; the tool calculates the minimum required area and checks existing CPCs.

Results

Minimum required CPC area -

Smallest standard size ≥ required -

k²S² -

I²t -

Worked example

I = 1000 A, t = 0.1 s, k = 115 (copper CPC per Table 54.3).

S = √(1000² × 0.1) / 115 = √100000 / 115 = 316.2 / 115 = 2.75 mm²

Next standard size up is 4.0 mm².

Check: 115² × 4² = 13225 × 16 = 211600 ≥ 100000 ✓

⚠️ Educational design aid. Verify all results against the current BS 7671 edition. Not a compliance tool - does not replace professional engineering judgement or BS 7671 table lookups.

Regulation reference: Per BS 7671 Regulation 543.1.3 and the adiabatic equation. The k values are from BS 7671 Table 54.3 (phase conductors) or Table 54.4 (bare conductors).