BS 7671:2018+A2:2022
The UK electrician's toolbox
Free BS 7671 compliant calculators for UK electricians. Cable sizing, voltage drop, max Zs, fault current and more. No sign-up required.
Essential Calculators
The tools sparkies use every day
Cable Size Calculator
Calculate the correct cable size for any circuit
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Voltage Drop Calculator
Check voltage drop against BS 7671 limits
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Max Zs Calculator
Maximum earth fault loop impedance values
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Fault Current Calculator
Calculate prospective fault current (PFC)
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Diversity Calculator
Maximum demand after diversity
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Ring Final Calculator
Ring circuit continuity and Zs verification
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Earthing & Bonding
CPC, main earthing and bonding conductor sizes
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Conduit Fill Calculator
Check conduit and trunking cable capacity
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Three Phase Balance
Balance loads across three phases
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EV Charger Calculator
Cable sizing and circuit requirements for EV chargers
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Motor Circuit Calculator
Cable sizing and protection for motor circuits
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Lighting Circuit Calculator
Cable sizing for lighting with inrush current
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BS 7671 Compliant
All calculations verified against BS 7671:2018+A2:2022 (18th Edition)
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SparkyHub is built by electricians, for electricians. Every calculator shows its working and references the relevant BS 7671 tables so you can verify the results yourself.
18th Edition CompliantShows WorkingBS 7671 References