BS 7671 cable-sizing verification

Fixed worked examples run through MEPCalc's cable-sizing and circuit-design calculations, compared line by line with the values printed in BS 7671:2018+A4:2026 and the IET On-Site Guide.

Result: 65 of 65 checks pass
Cases: 16 worked examples
Version / published: v1.4 · 2026-09-28
Engine fingerprint: c3b94d233cf2

Why we publish this

No formal certification scheme covers BS 7671 cable sizing. CIBSE TM33 tests building-services thermal software; nothing equivalent exists for the IET wiring regulations. So we publish our own evidence: a fixed set of worked examples, each with its expected value cited to the table, regulation and printed page it comes from, run through the same calculations our users run.

What these calculations do not model

Appendix 4 Equation 1 divides the device rating by its rating factors. The calculations apply ambient temperature, soil thermal resistivity, thermal insulation, the buried-cable factor and the depth-of-laying factor (Cd, Table 4B4, added by A4:2026); grouping comes from Table 4C1, or from Tables 4C2 and 4C3 for buried groups. Every buried case above is at the 0.7 m reference depth, where Cd is 1.00. One factor is deliberately not applied:

Semi-enclosed fuse to BS 3036 (Cf = 0.725) — the factor is implemented but no BS 3036 device can be selected, so it is 1.00 on every case above. A circuit protected by one is outside what these calculations cover.

How to read the tables

Expected is the value printed in the standard, or a hand calculation from printed values. The working is shown under each quantity.
Tolerance is exact for tabulated values and selected sizes, and ±2 % for calculated quantities such as voltage drop, earth-fault loop impedance and adiabatic conductor size.
Every check re-runs automatically whenever the calculation code changes, and this page is regenerated from those results. The engine fingerprint above identifies the calculation code the results came from.

Sources

BS 7671:2018+A4:2026
IET On-Site Guide 9th ed (2026)

Printed page numbers refer to the editions above.

Worked examples

CS-01

Flat twin-and-earth clipped direct — 21 A radial on a 25 A Type B breaker, 25 m

Inputs

Design current Ib = 21 A, single-phase 230 V
70 °C thermoplastic flat twin-and-earth, copper
Reference Method C (clipped direct), 25 m, ambient 30 °C, single circuit
Protective device In = 25 A (Type B circuit-breaker)

Checks for case CS-01
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Selected conductor size 1.5 mm² carries 20 A < 25 A; 2.5 mm² carries 27 A ≥ 25 A	2.5mm²	BS 7671:2018+A4:2026 Table 4D5, column 8, printed p484	2.5mm²	exact	Pass
Tabulated current-carrying capacity, It	27A	BS 7671:2018+A4:2026 Table 4D5, column 8 (2.5 mm²), printed p484	27A	exact	Pass
Tabulated voltage drop	18mV/A/m	BS 7671:2018+A4:2026 Table 4D5, column 9 (2.5 mm²), printed p484	18mV/A/m	exact	Pass
Voltage drop 18 mV/A/m × 21 A × 25 m ÷ 1000 = 9.45 V	9.45V	BS 7671:2018+A4:2026 Appendix 4 section 6, printed p457	9.45V	±2 %	Pass
Voltage-drop limit 5 % of 230 V = 11.5 V	11.5V	BS 7671:2018+A4:2026 Table 4Ab row a, other uses, printed p458	11.5V	exact	Pass

CS-02

Two-core 70 °C thermoplastic clipped direct — 40 A on a 40 A breaker, 10 m

Inputs

Design current Ib = 40 A, single-phase 230 V
Multicore 70 °C thermoplastic, non-armoured, copper (two-core)
Reference Method C (clipped direct), 10 m, ambient 30 °C, single circuit
Protective device In = 40 A

Checks for case CS-02
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Selected conductor size 4 mm² carries 36 A < 40 A; 6 mm² carries 46 A ≥ 40 A	6mm²	BS 7671:2018+A4:2026 Table 4D2A, column 6, printed p478	6mm²	exact	Pass
Tabulated current-carrying capacity, It	46A	BS 7671:2018+A4:2026 Table 4D2A, column 6 (6 mm²), printed p478	46A	exact	Pass
Tabulated voltage drop	7.3mV/A/m	BS 7671:2018+A4:2026 Table 4D2B, column 3 (6 mm²), printed p479	7.3mV/A/m	exact	Pass
Voltage drop 7.3 mV/A/m × 40 A × 10 m ÷ 1000 = 2.92 V	2.92V	BS 7671:2018+A4:2026 Appendix 4 section 6, printed p457	2.92V	±2 %	Pass

CS-03

Four-core 90 °C thermosetting SWA on perforated tray — 90 A three-phase on a 100 A device, 20 m

Inputs

Design current Ib = 90 A, three-phase 400 V
Multicore armoured 90 °C thermosetting, copper (three- or four-core)
Reference Method E (perforated cable tray), 20 m, ambient 30 °C, single circuit
Protective device In = 100 A

Checks for case CS-03
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Selected conductor size 16 mm² carries 99 A < 100 A; 25 mm² carries 131 A ≥ 100 A	25mm²	BS 7671:2018+A4:2026 Table 4E4A, column 5, printed p492	25mm²	exact	Pass
Tabulated current-carrying capacity, It	131A	BS 7671:2018+A4:2026 Table 4E4A, column 5 (25 mm²), printed p492	131A	exact	Pass
Tabulated voltage drop	1.65mV/A/m	BS 7671:2018+A4:2026 Table 4E4B, column 4, z (25 mm²), printed p493	1.65mV/A/m	exact	Pass
Voltage drop 1.65 mV/A/m × 90 A × 20 m ÷ 1000 = 2.97 V	2.97V	BS 7671:2018+A4:2026 Appendix 4 section 6, printed p457	2.97V	±2 %	Pass
Voltage-drop limit 5 % of 400 V = 20 V	20V	BS 7671:2018+A4:2026 Table 4Ab row a, other uses, printed p458	20V	exact	Pass

CS-04

Ambient 40 °C — 20 A two-core 70 °C thermoplastic clipped direct on a 20 A device, 10 m

Inputs

Design current Ib = 20 A, single-phase 230 V
Multicore 70 °C thermoplastic, non-armoured, copper (two-core)
Reference Method C (clipped direct), 10 m, ambient 40 °C, single circuit
Protective device In = 20 A

Checks for case CS-04
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Ambient-temperature rating factor, Ca	0.87	BS 7671:2018+A4:2026 Table 4B1, 70 °C thermoplastic at 40 °C, printed p469	0.87	exact	Pass
Required tabulated capacity, In ÷ (Ca·Cg·Cs·Ci·Cf·Cc) In ÷ Ca = 20 ÷ 0.87 = 22.99 A (Ib = In on this circuit)	22.99A	BS 7671:2018+A4:2026 Appendix 4 section 5.1.1, Equation 1, printed p453	22.99A	±2 %	Pass
Selected conductor size 1.5 mm² carries 19.5 A < 22.99 A; 2.5 mm² carries 27 A	2.5mm²	BS 7671:2018+A4:2026 Table 4D2A, column 6, printed p478	2.5mm²	exact	Pass
Tabulated current-carrying capacity, It	27A	BS 7671:2018+A4:2026 Table 4D2A, column 6 (2.5 mm²), printed p478	27A	exact	Pass

CS-05

Three circuits bunched — 20 A two-core 70 °C thermoplastic clipped direct on a 20 A device, 10 m

Inputs

Design current Ib = 20 A, single-phase 230 V
Multicore 70 °C thermoplastic, non-armoured, copper (two-core)
Reference Method C (clipped direct), 10 m, ambient 30 °C, three circuits bunched
Protective device In = 20 A

Checks for case CS-05
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Grouping rating factor, Cg	0.7	BS 7671:2018+A4:2026 Table 4C1, item 1, three circuits, printed p471	0.7	exact	Pass
Required tabulated capacity, In ÷ (Ca·Cg·Cs·Ci·Cf·Cc) In ÷ Cg = 20 ÷ 0.70 = 28.57 A (Ib = In on this circuit)	28.57A	BS 7671:2018+A4:2026 Appendix 4 section 5.1.2, Equation 2, printed p453	28.57A	±2 %	Pass
Selected conductor size 2.5 mm² carries 27 A < 28.57 A; 4 mm² carries 36 A	4mm²	BS 7671:2018+A4:2026 Table 4D2A, column 6, printed p478	4mm²	exact	Pass
Tabulated current-carrying capacity, It	36A	BS 7671:2018+A4:2026 Table 4D2A, column 6 (4 mm²), printed p478	36A	exact	Pass

CS-06

Buried direct in soil of 1.0 K·m/W at 25 °C — 32 A two-core 70 °C thermoplastic SWA on a 32 A device

Inputs

Design current Ib = 32 A, single-phase 230 V
Multicore armoured 70 °C thermoplastic, copper (two-core)
Reference Method D (buried direct), 30 m, soil thermal resistivity 1.0 K·m/W, ground 25 °C
Protective device In = 32 A

Checks for case CS-06
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Soil thermal-resistivity rating factor, Cs	1.5	BS 7671:2018+A4:2026 Table 4B3, direct buried cables at 1.0 K·m/W, printed p470	1.5	exact	Pass
Ambient-temperature rating factor, Ca	0.95	BS 7671:2018+A4:2026 Table 4B2, 70 °C thermoplastic at 25 °C ground, printed p469	0.95	exact	Pass
Buried-cable rating factor, Cc Cc = 0.9 for cables in a duct in the ground or buried direct	0.9	BS 7671:2018+A4:2026 Appendix 4 section 5.1.1, Equation 1 note (b), printed p453	0.9	exact	Pass
Required tabulated capacity, In ÷ (Ca·Cg·Cs·Ci·Cf·Cc) In ÷ (Ca × Cs × Cc) = 32 ÷ (0.95 × 1.50 × 0.9) = 24.95 A (Ib = In on this circuit)	24.95A	BS 7671:2018+A4:2026 Appendix 4 section 5.1.1, Equation 1, printed p453	24.95A	±2 %	Pass

CS-07

500 mm run in thermal insulation — 20 A two-core 70 °C thermoplastic on a 20 A device, 10 m

Inputs

Design current Ib = 20 A, single-phase 230 V
Multicore 70 °C thermoplastic, non-armoured, copper (two-core)
Reference Method C (clipped direct), 10 m, ambient 30 °C, 500 mm totally surrounded by thermal insulation
Protective device In = 20 A

Checks for case CS-07
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Thermal-insulation rating factor, Ci	0.5	BS 7671:2018+A4:2026 Appendix 4 section 2.6, length in insulation ≥ 500 mm (conductors up to 10 mm²), printed p451	0.5	exact	Pass
Required tabulated capacity, In ÷ (Ca·Cg·Cs·Ci·Cf·Cc) In ÷ Ci = 20 ÷ 0.50 = 40 A (Ib = In on this circuit)	40A	BS 7671:2018+A4:2026 Appendix 4 section 5.1.1, Equation 1, printed p453	40A	±2 %	Pass
Selected conductor size 4 mm² carries 36 A < 40 A; 6 mm² carries 46 A	6mm²	BS 7671:2018+A4:2026 Table 4D2A, column 6, printed p478	6mm²	exact	Pass
Tabulated current-carrying capacity, It	46A	BS 7671:2018+A4:2026 Table 4D2A, column 6 (6 mm²), printed p478	46A	exact	Pass

CS-08

Four-core 70 °C thermoplastic clipped direct — 50 A three-phase on a 50 A device, 40 m

Inputs

Design current Ib = 50 A, three-phase 400 V
Multicore 70 °C thermoplastic, non-armoured, copper (three- or four-core)
Reference Method C (clipped direct), 40 m, ambient 30 °C, single circuit
Protective device In = 50 A

Checks for case CS-08
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Selected conductor size 6 mm² carries 41 A < 50 A; 10 mm² carries 57 A	10mm²	BS 7671:2018+A4:2026 Table 4D2A, column 7, printed p478	10mm²	exact	Pass
Tabulated current-carrying capacity, It	57A	BS 7671:2018+A4:2026 Table 4D2A, column 7 (10 mm²), printed p478	57A	exact	Pass
Tabulated voltage drop	3.8mV/A/m	BS 7671:2018+A4:2026 Table 4D2B, column 4 (10 mm²), printed p479	3.8mV/A/m	exact	Pass
Voltage drop 3.8 mV/A/m × 50 A × 40 m ÷ 1000 = 7.6 V	7.6V	BS 7671:2018+A4:2026 Appendix 4 section 6, printed p457	7.6V	±2 %	Pass
Voltage-drop limit 5 % of 400 V = 20 V	20V	BS 7671:2018+A4:2026 Table 4Ab row a, other uses, printed p458	20V	exact	Pass

CS-09

Lighting circuit — 5 A on a 6 A Type B breaker, 1.0 mm² flat twin-and-earth clipped direct, 30 m

Inputs

Design current Ib = 5 A (the assumed load for a 6 A lighting circuit), single-phase 230 V
70 °C thermoplastic flat twin-and-earth, copper
Reference Method C (clipped direct), 30 m, ambient 30 °C, single circuit
Protective device In = 6 A (Type B circuit-breaker); lighting voltage-drop limit

The 5 A load for a 6 A lighting circuit is the IET On-Site Guide Table 7.1(i) assumption, printed p84.

Checks for case CS-09
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Selected conductor size 1.0 mm² carries 16 A ≥ 6 A	1mm²	BS 7671:2018+A4:2026 Table 4D5, column 8, printed p484	1mm²	exact	Pass
Tabulated voltage drop	44mV/A/m	BS 7671:2018+A4:2026 Table 4D5, column 9 (1.0 mm²), printed p484	44mV/A/m	exact	Pass
Voltage drop 44 mV/A/m × 5 A × 30 m ÷ 1000 = 6.6 V	6.6V	BS 7671:2018+A4:2026 Appendix 4 section 6, printed p457	6.6V	±2 %	Pass
Voltage-drop limit 3 % of 230 V = 6.9 V	6.9V	BS 7671:2018+A4:2026 Table 4Ab row a, lighting, printed p458	6.9V	exact	Pass

CS-10

Ring final circuit (IET On-Site Guide circuit A1) — 32 A Type B, 2.5/1.5 mm² flat twin-and-earth, 60 m loop, TN-C-S

Inputs

Ring final circuit, load 26 A (20 A at the far point plus the balance evenly distributed)
70 °C thermoplastic flat twin-and-earth, copper, 2.5 mm² line with 1.5 mm² protective conductor
Reference Method C (clipped direct), ring loop 60 m, ambient 30 °C
32 A Type B circuit-breaker, TN-C-S with Ze = 0.35 Ω, 0.4 s disconnection

Checks for case CS-10
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Selected conductor size	2.5mm²	IET On-Site Guide 9th ed (2026) Table H2.1, circuit A1, printed p218	2.5mm²	0.00 %	exact	Pass
Voltage drop 26 A over two parallel legs of L/2 is equivalent to L/4 = 15 m: 18 mV/A/m × 26 A × 15 m ÷ 1000 = 7.02 V	7.02V	IET On-Site Guide 9th ed (2026) Section 7.2.2 load model, printed p96; Table 7.1(i), printed p84	7.02V	0.00 %	±2 %	Pass
Earth-fault loop impedance, Zs Zs = Ze + (R1 + R2) × L/4 = 0.35 + 19.51 × 1.20 × 15 ÷ 1000 = 0.701 Ω	0.701Ω	IET On-Site Guide 9th ed (2026) Table I1 (2.5/1.5 mm² = 19.51 mΩ/m), printed p226; Table I3 (×1.20), printed p228	0.7012Ω	0.03 %	±2 %	Pass
Maximum Zs for the device	1.37Ω	BS 7671:2018+A4:2026 Table 41.3(a), Type B 32 A, printed p75	1.37Ω	0.00 %	exact	Pass

CS-11

Radial socket circuit (IET On-Site Guide circuit A2) — 32 A Type B, 26 A load, 4/1.5 mm² flat twin-and-earth, 20 m, TN-C-S

Inputs

Radial circuit, design current 26 A (the assumed load for a 32 A radial), single-phase 230 V
70 °C thermoplastic flat twin-and-earth, copper
Reference Method C (clipped direct), 20 m, ambient 30 °C
32 A Type B circuit-breaker, TN-C-S with Ze = 0.35 Ω, 0.4 s disconnection

The 26 A load for a 32 A radial is the IET On-Site Guide Table 7.1(i) assumption, printed p84.

Checks for case CS-11
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Selected conductor size BS 7671 Table 4D5 column 8: 2.5 mm² carries 27 A < 32 A; 4 mm² carries 37 A	4mm²	IET On-Site Guide 9th ed (2026) Table H2.1, circuit A2, printed p218	4mm²	exact	Pass
Voltage drop 11 mV/A/m × 26 A × 20 m ÷ 1000 = 5.72 V	5.72V	BS 7671:2018+A4:2026 Table 4D5, column 9 (4 mm² = 11 mV/A/m), printed p484	5.72V	±2 %	Pass
Earth-fault loop impedance, Zs Zs = 0.35 + 16.71 × 1.20 × 20 ÷ 1000 = 0.751 Ω	0.751Ω	IET On-Site Guide 9th ed (2026) Table I1 (4/1.5 mm² = 16.71 mΩ/m), printed p226; Table I3 (×1.20), printed p228	0.751Ω	±2 %	Pass
Maximum Zs for the device	1.37Ω	BS 7671:2018+A4:2026 Table 41.3(a), Type B 32 A, printed p75	1.37Ω	exact	Pass

CS-12

The same radial on a 32 A Type C breaker — earth-fault loop impedance governs the size

Inputs

Radial circuit, design current 26 A, single-phase 230 V
70 °C thermoplastic flat twin-and-earth, copper
Reference Method C (clipped direct), 20 m, ambient 30 °C
32 A Type C circuit-breaker, TN-C-S with Ze = 0.35 Ω, 0.4 s disconnection

Checks for case CS-12
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Maximum Zs for the device	0.68Ω	BS 7671:2018+A4:2026 Table 41.3(b), Type C 32 A, printed p75	0.68Ω	0.00 %	exact	Pass
Selected conductor size 4/1.5 mm² gives Zs = 0.751 Ω > 0.68 Ω, so the next size, 6/2.5 mm², is needed	6mm²	IET On-Site Guide 9th ed (2026) Table I1 (6/2.5 mm² = 10.49 mΩ/m), printed p226	6mm²	0.00 %	exact	Pass
Earth-fault loop impedance, Zs Zs = 0.35 + 10.49 × 1.20 × 20 ÷ 1000 = 0.602 Ω ≤ 0.68 Ω	0.602Ω	IET On-Site Guide 9th ed (2026) Table I1 (6/2.5 mm² = 10.49 mΩ/m), printed p226; Table I3 (×1.20), printed p228	0.6018Ω	0.03 %	±2 %	Pass

CS-13

Adiabatic check — copper protective conductor in a 70 °C thermoplastic cable, 6 kA for 0.1 s

Inputs

Fault current I = 6000 A, disconnection time t = 0.1 s
Copper protective conductor incorporated in a 70 °C thermoplastic cable
Installed conductor 25 mm² (used only for the pass/fail comparison)

Checks for case CS-13
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Adiabatic constant, k	115	BS 7671:2018+A4:2026 Table 54.3, copper, 70 °C thermoplastic, printed p210	115	0.00 %	exact	Pass
Minimum conductor size, S S = √(I²t) ÷ k = √(6000² × 0.1) ÷ 115 = 1897.4 ÷ 115 = 16.5 mm²	16.5mm²	BS 7671:2018+A4:2026 Regulation 543.1.3, printed p209	16.5mm²	0.00 %	±2 %	Pass

CS-14

Adiabatic check — steel wire armour of a 90 °C thermosetting cable as the protective conductor, 10 kA for 0.4 s

Inputs

Fault current I = 10 000 A, disconnection time t = 0.4 s
Steel wire armour of a 90 °C thermosetting cable used as the protective conductor
Installed armour 150 mm² (used only for the pass/fail comparison)

Checks for case CS-14
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Adiabatic constant, k	46	BS 7671:2018+A4:2026 Table 54.4, steel, 90 °C thermosetting, printed p210	46	0.00 %	exact	Pass
Minimum conductor size, S S = √(10 000² × 0.4) ÷ 46 = 6324.6 ÷ 46 = 137.5 mm²	137.5mm²	BS 7671:2018+A4:2026 Regulation 543.1.3, printed p209	137.49mm²	0.01 %	±2 %	Pass

CS-15

The worked example printed in BS 7671 Appendix 4 — 58 A three-phase on a perforated tray with three other circuits, 35 °C

Inputs

Design current Ib = 58 A, three-phase 400 V
Four-core 90 °C thermosetting insulated cable with steel wire armour, copper
Reference Method E (perforated cable tray), single layer, in a group with three other circuits
Ambient 35 °C, 20 m
Protective device In = 63 A (circuit-breaker to BS EN 60898-1)

This is the only worked example printed in Appendix 4. It appears at section 5.5.2 as the no-harmonics base case before the third-harmonic cases that follow it.

Checks for case CS-15
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Ambient-temperature rating factor, Ca	0.96	BS 7671:2018+A4:2026 Table 4B1, 90 °C thermosetting at 35 °C, printed p469	0.96	exact	Pass
Grouping rating factor, Cg	0.77	BS 7671:2018+A4:2026 Table 4C1 item 3, four circuits on a perforated cable tray, printed p471	0.77	exact	Pass
Selected conductor size It = In ÷ (Ca × Cg) = 63 ÷ (0.96 × 0.77) = 85.2 A; Table 4E4A column 5: 10 mm² carries 78 A < 85.2 A, 16 mm² carries 99 A ≥ 85.2 A	16mm²	BS 7671:2018+A4:2026 Appendix 4 section 5.5.2 worked example, printed p455	16mm²	exact	Pass
Tabulated current-carrying capacity, It	99A	BS 7671:2018+A4:2026 Table 4E4A, column 5 (16 mm²), printed p492	99A	exact	Pass

CS-16

Three circuits buried direct and touching, soil 1.0 K·m/W at 25 °C — 32 A two-core 70 °C thermoplastic SWA on a 32 A device

Inputs

Design current Ib = 32 A, single-phase 230 V
Multicore armoured 70 °C thermoplastic, copper (two-core)
Reference Method D (buried direct), 30 m, soil thermal resistivity 1.0 K·m/W, ground 25 °C
Group of three circuits, cables touching
Protective device In = 32 A

Table 4C1's own Reference Method column reads A to F; buried groups take Tables 4C2 (buried direct) or 4C3 (in buried ducts), printed p472, both keyed by clearance as well as circuit count.

Checks for case CS-16
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Soil thermal-resistivity rating factor, Cs	1.5	BS 7671:2018+A4:2026 Table 4B3, direct buried cables at 1.0 K·m/W, printed p470	1.5	exact	Pass
Ambient-temperature rating factor, Ca	0.95	BS 7671:2018+A4:2026 Table 4B2, 70 °C thermoplastic at 25 °C ground, printed p469	0.95	exact	Pass
Grouping rating factor, Cg Table 4C1 item 1 (Methods A to F) would give 0.70 — Table 4C2 is the table printed for Reference Method D	0.65	BS 7671:2018+A4:2026 Table 4C2, three circuits, cables touching (nil clearance), printed p472	0.65	exact	Pass
Buried-cable rating factor, Cc Cc = 0.9 for cables in a duct in the ground or buried direct	0.9	BS 7671:2018+A4:2026 Appendix 4 section 5.1.1, Equation 1 note (b), printed p453	0.9	exact	Pass
Required tabulated capacity, In ÷ (Ca·Cg·Cs·Ci·Cf·Cc) In ÷ (Ca × Cg × Cs × Cc) = 32 ÷ (0.95 × 0.65 × 1.50 × 0.9) = 38.39 A (Ib = In on this circuit); with Table 4C1's 0.70 it would be 35.64 A	38.39A	BS 7671:2018+A4:2026 Appendix 4 section 5.1.2, Equation 2, printed p453	38.39A	±2 %	Pass
Selected conductor size 4 mm² carries 38 A < 38.39 A; 6 mm² carries 48 A ≥ 38.39 A — with Table 4C1's 0.70 the 4 mm² cable (38 A ≥ 35.64 A) would have been selected, one size too small	6mm²	BS 7671:2018+A4:2026 BS 7671:2018+A4:2026 Table 4D4A, column 8 (Reference Method D2, direct in ground), page 482	6mm²	exact	Pass
Tabulated current-carrying capacity, It	48A	BS 7671:2018+A4:2026 BS 7671:2018+A4:2026 Table 4D4A, column 8 (6 mm², Reference Method D2), page 482	48A	exact	Pass