Cable selection

Cable current-carrying capacity (Iz)

Applies the standard Iz = It × Ca × Cg × Ci calculation for a 70°C thermoplastic copper cable to reference method C (clipped direct). Verifies the two BS 7671 coordination rules: I_b ≤ I_n ≤ I_z.

Cable size

Ca — ambient temperature

1.00 at 30 °C; 0.87 at 40 °C; 0.71 at 50 °CCg — grouping

1.00 single; 0.80 two circuits; 0.70 three; etc.Ci — thermal insulation

1.00 uncovered; 0.75 in insulation > 500 mm; 0.50 fully surroundedDesign current Ib

Device rating In

Results

Tabulated It27.0A

Effective Iz27.0A

Ib ≤ In?Yes

In ≤ Iz?Yes