SPARKY STUDY NOTES sparkystudynotes.co.uk/learn/a-cooker-circuit-cable-calculation-on-one-page
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A cooker circuit cable calculation, on one pageThe whole design, in a minute.
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| Step | Result | Where from |
|---|---|---|
| Device requirements | 30 mA RCD + AFDD → RCBO with AFDD | Regs 411.3.3, 522.6.202, 421.1.7 |
| Cable type | 70 °C thermoplastic T&E | Table 4A1 |
| Installation methods | B (trunking) · A (insulating wall) | Table 4A2 |
| Ib full load | 9600 ÷ 230 = 41.7 A | P ÷ V |
| Ib after diversity | 24.5 A | OSG Table A2 |
| In | 32 A Type B | (OSG Table B6 lists sizes) |
| Ca · Cg | 0.94 · 0.7 | Tables 4B1 · 4C1 |
| It needed | 32 ÷ (0.94 × 0.7) = 48.6 A | App 4 formula |
| Cable | 16 mm² T&E, 57 A (Method A) | Table 4D5 |
| Voltage drop | 1.85 V ≤ 11.5 V ✓ | Table 4D5 · Table 4Ab |
| Overload | Iz 37.5 A · I2 46.4 A ≤ 54.4 A ✓ | Reg 433.1.1 |
| R1 + R2 | 4.23 × 1.2 × 27 ÷ 1000 = 0.137 Ω | GN3 Tables B1, B3 |
| Zs | 0.26 + 0.137 = 0.397 Ω ≤ 1.37 Ω ✓ | Table 41.3 |
| Max disconnection time | 0.4 s | Table 41.1 |
| PEFC | 230 × 0.95 ÷ 0.397 = 550.4 A | Ohm's law with Cmin |
| Ia | 160 A → trips in 0.1 s ✓ | App 3 Fig 3A4 |
| Adiabatic | 1.51 mm² min · 6 mm² CPC ✓ | Table 54.3 (k = 115) |
Sparky's closing tip
Try the blank scenario yourself, and make your own version the same way. Change the load, the length, Ze, the grouping or the temperature and work it through. It looks hard, but it's a logical step-by-step process. Apart from the adiabatic equation, it's no harder than Ohm's law. Not many electricians could design a circuit like this without serious revision. The aim is to get "robotic" about it.
Try the blank scenario yourself, and make your own version the same way. Change the load, the length, Ze, the grouping or the temperature and work it through. It looks hard, but it's a logical step-by-step process. Apart from the adiabatic equation, it's no harder than Ohm's law. Not many electricians could design a circuit like this without serious revision. The aim is to get "robotic" about it.
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