BS 7671 (UK IET Wiring Regulations) Compliant Calculators
⚠️ Important Disclaimer: These calculators are based on BS 7671 (UK IET Wiring Regulations). For accurate design calculations, always refer to the latest BS 7671 standard, manufacturer's data, and consult with a qualified electrical engineer. This tool should not be used as the sole basis for design decisions.
Standards: This calculator complies with BS 7671 The IET Wiring Regulations
Voltage Range: Up to and including 0.6/1 kV AC (1.5 kV DC)
Includes: Grouping factors, thermal insulation factors, more detailed cable tables, and mV/A/m values for voltage drop
BS 7671 Table 4C1 - Grouping correction factors
BS 7671 Table 52.2 - Thermal insulation correction
Affects current-carrying capacity
Standard: Based on BS 7671 and typical UK installation practices
Purpose: Calculate the maximum demand for consumers' mains and sub-mains
Uses standard diversity factors from BS 7671 Appendix C for lighting, heating, cooking, etc.
BS 7671 Appendix C Diversity Factors:
Standard: BS 7671 Table 54.7
Purpose: Calculate minimum cross-sectional area of protective conductor
Formula: S = √(I²t) / k
Where: S = Minimum CSA (mm²), I = Fault current (A), t = Disconnection time (s), k = Factor
Standard: BS 7671 Table 54.8
Purpose: Calculate minimum size for main protective bonding conductors
Standard: BS 7671 Tables 41.2, 41.3, 41.4
Purpose: Calculate maximum earth fault loop impedance for protective devices
Uses exact Zs values for all device types including specific fuse types (BS 88, BS 1361, BS 3036)
Comprehensive Mode Features:
Voltage uncertainty factor per BS 7671
Standard: BS 7671 Appendix 4
Maximum Allowable: 3% for lighting, 5% for other circuits
Uses accurate mV/A/m values which include both resistance and reactance components
From BS 7671 Appendix 4 Table 4D2B, 4D4B, etc. (mV/A/m)
Standard: BS 7671 defines TN-S, TN-C-S, TT, and IT systems
Description: Separate neutral and protective conductors throughout the installation.
Characteristics: Earth and neutral are separate from the supply transformer to the installation.
Common Use: Older UK installations, some new installations.
Description: Combined neutral and earth (PEN) up to the installation, then separated.
Characteristics: Most common in UK. Earth and neutral combined in supply, separated at service head.
Common Use: Modern UK installations, PME (Protective Multiple Earthing).
Description: No earth provided by supply, installation has its own earth electrode.
Characteristics: Requires RCD protection. Earth electrode resistance must be low enough for disconnection.
Common Use: Rural installations, where PME is not available.
Description: Isolated or impedance-earthed neutral system.
Characteristics: No direct connection to earth. Used for continuity of supply.
Common Use: Hospitals, data centers, critical installations.
Note: Always verify the earthing system type before designing or modifying an installation. Incorrect assumptions can lead to dangerous conditions.
Standard: BS 7671 Regulation 434.1, Appendix 3
Purpose: Calculate prospective fault current (PFC) at a point in the installation
Standard: BS 7671 Regulation 411.4, Tables 41.2-41.4
Purpose: Calculate actual Zs and compare with maximum allowed Zs
Voltage uncertainty factor per BS 7671
Standard: BS 7671 Regulations 411.3, 531.2, Table 53.1
Purpose: Select appropriate RCD type and rating for circuit protection
Standard: BS 7671 Regulation 536.4
Purpose: Verify discrimination between upstream and downstream protective devices
Standard: BS 7671 Regulation 552.1, Appendix 4
Purpose: Calculate motor starting current and cable sizing requirements
Standard: BS 7671 Appendix E, Tables E1-E5
Purpose: Calculate cable fill percentage in conduits and trunking
Standard: BS 7671 Regulation 542.2, Appendix 14
Purpose: Calculate earth electrode resistance for TT systems
Standard: BS 7671 Appendix C
Purpose: Calculate maximum demand using load factors and diversity
Standard: BS 7671 / IET Guidance Note 3 (BS 7671:2018+A3:2024)
Enter measured end-to-end resistance values from continuity testing. Verifies r2, per-outlet Zs, and ring integrity.
Standard: BS 7671 Section 4 — Balanced and unbalanced 3-phase systems
Calculate total active, reactive, and apparent power. Voltage imbalance flagged above 2% per NEMA MG-1.
Enter per-phase line-to-neutral voltage, current, and power factor for each phase.
Standard: BS 7671, IEC 61000-3-2 — Capacitor bank sizing for PF improvement
Calculates required kVAR and capacitor size to improve power factor from current to target value.
Standard: BS 7671:2018+A3:2024 Section 722, IET Code of Practice for EV Charging 5th Ed.
Calculates cable size, protection, and compliance requirements for EV charge point installations.
Standard: BS 7671:2018+A2:2022 Regulation 421.1.7 — Arc Fault Detection Devices
Determines whether AFDD protection is mandatory or recommended based on premises type and circuit.
Standard: BS 7671 Appendix 4, Table 4C1 — Correction factors for groups of cables
Applies the grouping correction factor Cg to the base current-carrying capacity of a cable.
Standard: BS 7671 Section 712, BS 7671:2018+A3:2024 (bidirectional devices), EREC G98/G99
Sizes DC string cables, inverter AC output, and checks G98/G99 connection threshold and bidirectional device requirements.
Standard: BS 7671:2018+A4:2026 (new Chapter — effective October 2026), BS EN IEC 62933-5-2
Checks installation location suitability and cable/protection sizing for Electrical Energy Storage Systems. Based on Amendment 4 requirements (April 2026).
Standard: IEC 60076, BS 7671 Section 5 — Transformer selection and sizing
Calculates minimum kVA rating and recommends the next standard size with a safety margin.
Standard: Engineering Recommendation EREC G5.4 (400V planning level: 5% THD)
Enter measured harmonic currents to calculate THD%, total RMS current, and assess power quality compliance.
Standard: BS 7671:2018+A4:2026 (new section), IEEE 802.3bt, IEC 60512-99-001
Calculates total bundle power and required derating for PoE cables. Amendment 4 (October 2026) introduces specific BS 7671 requirements for PoE installations.