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Equipment Catalogue
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Every calculation, basket item, labour entry and estimate is saved automatically — persists when you close and reopen the app
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Cable Calculator BS 7671:2018+A4:2026
Describe the job — the app recommends the correct cable type and size automatically
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Circuit Parameters
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Advanced / Protection
⚡
Select a circuit application and enter the load and run length.The calculator will recommend the correct cable type and size.
Cable Schedule
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Full Estimate
Complete job estimate with markup and VAT
Zs Look-up Table
Maximum earth fault loop impedance — BS 7671 Appendix 3, with Cmin = 0.95 applied (Reg 411.4.4)
Formula: Zs(max) = (U0 × Cmin) / Ia = (230 × 0.95) / Ia
Ohm's Law Wheel
Enter any two known values — the other two are calculated automatically
💡 Input Values
📊 Results
Enter any two values to calculate the rest.
📖 Formula Reference
Voltage (V)
V = I × R
V = P / I
V = √(P × R)
V = P / I
V = √(P × R)
Current (I)
I = V / R
I = P / V
I = √(P / R)
I = P / V
I = √(P / R)
Resistance (R)
R = V / I
R = V² / P
R = P / I²
R = V² / P
R = P / I²
Power (P)
P = V × I
P = I² × R
P = V² / R
P = I² × R
P = V² / R
R1+R2 Calculator
Earth fault loop resistance for Twin & Earth and SWA cables at 70°C — BS 7671 Table 54.7
🧮 Cable Parameters
📈 Results
Select parameters to calculate.
Conduit Fill Calculator
Cable space factor per BS 7671 Table 5A & Appendix 5 — max 45% fill for 2+ cables
🔧 Conduit Parameters
Cables
📊 Fill Analysis
Add cables to calculate fill.
📖 Conduit Capacity Reference
| Size | Internal Area (mm²) | 45% Fill (mm²) | Max 1.5mm² cables | Max 2.5mm² cables |
|---|
🧰 V3 Toolbox
17 engineering modules — tap any card to open · V3.5 Engine
⚙ DESIGN ESTIMATOR
Three-Phase Balance
Calculate neutral current from unbalanced phase loads
Phase Currents (A)
Result
Enter phase currents.
⚙ DESIGN ESTIMATOR
Motor Circuit Sizing
kW/HP to Amps with Type C/D breaker recommendation — BS 7671 Reg 552
Motor Parameters
Motor Circuit Design
Enter motor parameters.
⚙ DESIGN ESTIMATOR
Sub-Main Sizer
SWA cable sizing for distribution runs — 1.5% to 3% volt drop limit
Distribution Parameters
Cable Selection
Enter parameters.
⚙ DESIGN ESTIMATOR
kW ↔ Amps Converter
Single-phase 230V and three-phase 400V conversion
Converter
Result
Enter values.
⚙ DESIGN ESTIMATOR
Heat Pump Calculator
Circuit sizing from heat output and COP — Type C MCB recommended
Heat Pump Data
Circuit Design
Enter heat pump data.
⚙ DESIGN ESTIMATOR
Battery Storage (BESS) — DC Cable Sizer
DC cable sizing for 48V/400V battery systems targeting <1% volt drop
BESS Parameters
DC Cable Size
Enter BESS parameters.
✓ COMPLIANCE CHECK
EV PME Safety Checker
Automated warning for PME supply on outdoor EV chargers — Reg 722.411.4.1
Installation Conditions
Reg 722.411.4.1 — Background
PME earth cannot be used for outdoor EV charging without:
✅ Open-PEN detection device
✅ Separate TT earth electrode
PEN failure can raise vehicle chassis to line voltage — fatal shock risk.
✅ Separate TT earth electrode
✓ COMPLIANCE CHECK
RCD Selection Guide
Quick lookup for Type A, B and F requirements — Amendment 2 restrictions apply
Circuit Details
RCD Recommendation
Select circuit type.
✓ COMPLIANCE CHECK
DNO G98 / G99 Checker
Check solar/battery export against 16A per phase limit — EREC G98/G99
Generation System
G98 / G99 Decision
Enter system details.
✓ COMPLIANCE CHECK
Ring Final Circuit (RFC) Calc
32A ring sizing with 100m² floor area limit check — BS 7671 Appendix 15
Ring Parameters
RFC Check
Enter RFC parameters.
✓ COMPLIANCE CHECK
Disconnection Time Verifier
Verify if Zs meets 0.4s or 5s requirement — BS 7671 Table 41.1
Circuit Data
Disconnection Check
Enter Zs to verify.
✓ COMPLIANCE CHECK
Consumer Unit Configurator
Checklist for SPD, AFDD, RCD layout — BS 7671 Reg 421.1.7 / 443.4 / 531.3
Installation Details
Compliance Checklist
ℹ GUIDANCE TOOL
Selectivity — Preliminary Ratio Screening
Simplified fuse vs MCB ratio — preliminary check only. Verify with manufacturer TCC curves.
Upstream Device
Downstream Device
Selectivity Check
Enter device ratings.
ℹ GUIDANCE TOOL
SWA Gland & Cleat Lookup
BW/CW gland and cleat reference for XLPE SWA cable — BS 6121
Cable Selection
Result
Select cable parameters.
ℹ GUIDANCE TOOL
Lighting & Cooker Circuits
Built-in diversity maths — IET On-Site Guide Table 1B
💡 Lighting Diversity
🍳 Cooker Circuit (10A + 30%)
🔌 Socket Circuits (100% + 40%)
🚿 Shower / Immersion
✓ COMPLIANCE CHECK
Circuit Breaker Selector
Standard ratings 6A–125A — Ib ≤ In ≤ Iz — BS 7671 Reg 433.1
Circuit Parameters
Breaker Selection
Enter Ib and Iz.