Shower Circuit Voltage Drop Calculator
Check voltage drop compliance for electric shower circuits - 8.5kW to 10.5kW
Shower Circuit Quick Facts
- 8.5kW shower = 37A, 9.5kW = 41A, 10.5kW = 46A (at 230V)
- Standard cable: 6mm² for up to 9kW, 10mm² for 9.5kW+ or long runs
- Showers draw full rated current whenever running - no diversity
- Dedicated radial circuit required - cannot share with other loads
- MCB typically 40A or 45A Type B depending on shower rating
Values from BS 7671 Table 4D1B (PVC copper at 70°C)
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Common Shower Circuit Scenarios
8.5kW shower - short run (10m)
37A with 6mm² (7.3 mV/A/m). At 10m: (7.3 × 37 × 10) ÷ 1000 = 2.70V (1.17%) ✓
9.5kW shower - typical run (15m)
41A with 10mm² (4.4 mV/A/m). At 15m: (4.4 × 41 × 15) ÷ 1000 = 2.71V (1.18%) ✓
10.5kW shower - standard (15m)
46A with 10mm² (4.4 mV/A/m). At 15m: (4.4 × 46 × 15) ÷ 1000 = 3.04V (1.32%) ✓
10.5kW shower - long run (25m)
46A with 10mm². At 25m: (4.4 × 46 × 25) ÷ 1000 = 5.06V (2.20%) ✓
High-power 11kW+ shower
48A+ load requires 10mm² minimum. Check manufacturer specs and consider 16mm² for long runs
Related High-Power Circuits
Installing a cooker circuit? Similar cable sizing considerations apply. For cable current capacity, use our cable sizing calculator. See our main voltage drop calculator for all circuit types.
Shower Circuit Voltage Drop
Electric showers draw their full rated current whenever running - there is no diversity factor. A 10.5kW shower pulls 46A continuously during use. This high current over typical bathroom cable runs (10-20m) means voltage drop must be carefully calculated to ensure the shower operates at full power.
Shower Circuit Installation Costs (2024)
Typical UK installation costs. Shower unit costs vary widely (£150-600).
| Installation Scenario | Materials | Labour | Total |
|---|---|---|---|
| Simple shower circuit (10m) | £80-150 | £150-250 | £230-400 |
| Standard install (15-20m) | £120-220 | £200-350 | £320-570 |
| Long run or difficult route | £180-350 | £300-500 | £480-850 |
| CU upgrade needed | +£150-350 | +£150-300 | +£300-650 |
| Shower unit replacement only | £200-500 | £80-150 | £280-650 |
Prices as of 2024. Excludes shower unit cost.
Why Shower Voltage Drop Matters
If voltage drop is excessive, the shower will not heat water properly. Modern showers have thermal cut-outs that may trip if the element overheats due to low voltage. Users experience lukewarm water or intermittent heating. Proper cable sizing ensures full power delivery and reliable operation.
Shower Current Calculation
Electric shower current is calculated as Power ÷ Voltage. At UK nominal 230V: 8.5kW = 37A, 9.5kW = 41A, 10.5kW = 46A, 11kW = 48A. These are continuous loads with no diversity - the shower draws full current whenever in use.
Frequently Asked Questions
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