About SparkyHub
Free calculators and references for UK electricians. No sign-up, no ads, no faff.
What is SparkyHub?
SparkyHub is a collection of 54 free calculators and 52 reference guides for UK electricians. Cable sizing, voltage drop, max Zs, fault current, diversity, conduit fill, and more.
Every calculation is based on BS 7671:2018+A2:2022. We show the formulas, table references, and working so you can verify results yourself. No black boxes.
No accounts. No email capture. No premium tier. Open a calculator and get your answer. That's it.
How We Verify Accuracy
All calculations are cross-referenced against published BS 7671 tables and the IET On-Site Guide. Results are tested against known values from these sources to ensure accuracy.
Each calculator shows which BS 7671 table or regulation its values come from, so you can look them up yourself.
Standards Referenced
- BS 7671:2018+A2:2022 (18th Edition Wiring Regulations)
- IET On-Site Guide (8th Edition)
- IET Guidance Note 1: Selection & Erection
- IET Guidance Note 3: Inspection & Testing
BS 7671 Tables Used
- • Tables 4D1A–4J1 (current carrying capacity)
- • Tables 4D1B–4J2B (voltage drop mV/A/m values)
- • Tables 41.2–41.4 (maximum Zs values)
- • Tables 4B1, 4C1, 52.2 (correction factors)
- • Tables 54.2–54.8 (earthing & bonding conductor sizes)
- • Appendix 5 (conduit & trunking fill factors)
Who is it for?
- Qualified electricians who need quick calculations on site
- Apprentices learning the trade and studying for AM2 and 2391
- Contractors pricing jobs and designing installations
- Inspectors verifying calculations during EICR inspections
Disclaimer
These tools are provided for guidance only. The responsibility for any electrical installation lies with the qualified person carrying out the work. Always verify calculations independently and apply professional judgement.
Found an error? Let us know and we'll fix it. We'd rather be corrected than have sparkies using wrong values.
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