TradeCalculator.co.uk
Cable Ampacity Table — Current Carrying Capacity
Current carrying capacity for common UK cable sizes by installation method and insulation type, referencing BS 7671:2018 Tables 4D1A to 4D5A.
Twin-and-Earth (T+E) Flat Cable — PVC Insulated (70°C)
Reference: BS 7671:2018 Table 4D5A, Column 6 (Method C — clipped direct) and Column 4 (Method A — enclosed in insulation).
| Cable Size (mm²) | Method A — Enclosed (A) | Method B — Conduit (A) | Method C — Clipped (A) | Typical Use |
|---|---|---|---|---|
| 1.0 | 11 | 13 | 16 | Lighting circuits (6A MCB) |
| 1.5 | 14 | 16.5 | 20 | Lighting, immersion (long runs) |
| 2.5 | 18.5 | 23 | 27 | Ring finals (32A), radials (20A) |
| 4.0 | 25 | 30 | 37 | Cooker circuits, radials (32A) |
| 6.0 | 32 | 38 | 47 | Cooker circuits, shower (40A) |
| 10.0 | 43 | 52 | 64 | Electric shower (45-50A), EV charger |
| 16.0 | 57 | 69 | 85 | Submain supplies, large loads |
SWA Cable — XLPE Insulated (90°C)
Reference: BS 7671:2018 Table 4E4A (90°C thermosetting/XLPE armoured). Two-core SWA for single-phase, three- or four-core for three-phase. Clipped direct (Method C). For 70°C PVC SWA see Table 4D4A values on our UK cable sizes page.
| Cable Size (mm²) | 2-Core (Single Phase) (A) | 4-Core (Three Phase) (A) | Typical Use |
|---|---|---|---|
| 1.5 | 27 | 23 | Lighting submains |
| 2.5 | 36 | 31 | External circuits, outbuildings |
| 4.0 | 49 | 42 | Outbuildings, EV chargers |
| 6.0 | 62 | 53 | Garage/workshop supplies |
| 10.0 | 85 | 73 | Submain supplies |
| 16.0 | 110 | 94 | Main supply cables |
| 25.0 | 146 | 124 | Large commercial supplies |
Ambient Temperature Correction Factors
Reference: BS 7671 Table 4B1. Multiply tabulated current by the factor below.
| Ambient Temp (°C) | PVC (70°C rated) | XLPE (90°C rated) |
|---|---|---|
| 25 | 1.03 | 1.02 |
| 30 | 1.00 | 1.00 |
| 35 | 0.94 | 0.96 |
| 40 | 0.87 | 0.91 |
| 45 | 0.79 | 0.87 |
| 50 | 0.71 | 0.82 |
Grouping Correction Factors
Reference: BS 7671 Table 4C1. Apply when cables are bunched together or in the same enclosure.
| No. of Circuits | Enclosed or Bunched | Single Layer Clipped |
|---|---|---|
| 1 | 1.00 | 1.00 |
| 2 | 0.80 | 0.85 |
| 3 | 0.70 | 0.79 |
| 4 | 0.65 | 0.75 |
| 5 | 0.60 | 0.73 |
| 6 | 0.57 | 0.72 |
Note: Values shown are indicative. Always refer to BS 7671:2018 + Amendment 2:2022 Tables 4D1A-4D5A for definitive current ratings. Design must account for all applicable correction factors.
Related Pages
See the UK Cable Sizes reference, the Voltage Drop Coefficients table, and the BS 7671 Domestic Circuit Guide.
Next up: related pages
Frequently Asked Questions
Ampacity (current carrying capacity) is the maximum continuous current a cable can safely carry without exceeding its temperature rating. It depends on the cable size (cross-sectional area in mm²), insulation type (PVC at 70°C or XLPE/LSF at 90°C), installation method (clipped direct, in conduit, in trunking, etc.), ambient temperature, and grouping with other cables. BS 7671 Tables 4D1A-4D5A provide reference values for standard conditions.
BS 7671 defines installation methods in Table 4A2. Common methods include: Method A (enclosed in insulation), Method B (enclosed in conduit/trunking on a wall), Method C (clipped direct to a surface), and Reference Method 100 (in free air on a cable tray). Cables clipped direct (Method C) can carry more current than those enclosed in insulation (Method A) because heat dissipates more freely.
The tabulated values assume an ambient temperature of 30°C, no grouping with other cables, and no thermal insulation contact. You must apply correction factors for: ambient temperature other than 30°C (Table 4B1), grouping of cables (Table 4C1-4C5), thermal insulation contact (Regulation 523.9), and depth of burial for underground cables. Multiply the tabulated current by all applicable factors.
A 32A ring final circuit typically uses 2.5 mm² twin-and-earth (T+E) cable with PVC insulation. The ring topology means current is shared between both legs of the ring, so the design current per conductor is significantly less than 32A. However, this only applies if the ring is correctly wired with no interconnections or spurs exceeding the permitted limits per BS 7671.
PVC (polyvinyl chloride) insulated cables are rated to 70°C maximum conductor temperature and have lower current ratings. XLPE (cross-linked polyethylene) and LSF (low smoke and fume) cables are rated to 90°C and can carry approximately 20-30% more current for the same cable size. SWA (steel wire armoured) cables with XLPE insulation are commonly used for submain supplies and outdoor installations.
Related Calculators
Was this calculator helpful?
Last updated: April 2026
Verified against UK standards · estimates only, confirm with your supplier.