Built by engineers,
for engineers
CableSpec was created because every engineer carrying out cable sizing to BS7671 Appendix 4 deserves a tool that does the maths correctly - every check, every correction factor, the reactive VD formula, and the right disconnection times for the right earthing system. Every time.
Industry-specific
Every feature is built specifically for BS7671 cable sizing work. No generic tooling, no compromise - just a rigorous, complete implementation of the Appendix 4 methodology that electrical engineers can rely on.
Standards-referenced
CableSpec follows BS7671:2018+A4:2026 Appendix 4 throughout - every check, every correction factor, the reactive voltage drop formula, the Reg 433.1.201–204 overload rules and the right disconnection times per earthing system.
Audit-ready output
Every calculation produces a professional PDF certificate showing all inputs, correction factors, check results and engineer details - giving clients and inspectors everything they need without additional documentation.
The BS7671 cable sizing tool the industry has been waiting for
CableSpec is a cloud-based SaaS application purpose-built for BS7671:2018+A4:2026 cable sizing calculations. It gives electrical design engineers and contractors a rigorous, auditable, document-ready way to size cables for any circuit on any project - from a simple domestic radial to a complex three-phase sub-main with parallel SWA cables on an underground route.
Before CableSpec, cable sizing typically happened in a spreadsheet - if not from memory. Correction factors were applied inconsistently, the reactive VD formula was often omitted, the 0.725 factor for BS 3036 fuses was forgotten, and the right disconnection time for TT earthing was a matter of engineer knowledge rather than automatic application. CableSpec eliminates these failure modes by implementing the complete Appendix 4 methodology in a single, auditable calculation engine.
- Every Appendix 4 check per circuit - all automated
- Every correction factor, with individual values shown on the certificate
- Reactive VD formula (Ir·cosφ + Ix·sinφ) for large conductors
- Overload rules per device type and installation (Regs 433.1.201–204)
- Correct disconnection time per earthing system and circuit type
- Professional PDF certificate per circuit with engineer name and date
- Full project schedule and compliance summary in PDF and CSV
- Complete version history on every circuit - timestamped, attributed
Specialist software, built from inside the industry
Construct Software is a specialist software development company whose entire product portfolio is focused on the UK electrical contracting and building services sector. Every tool we build addresses specific technical, regulatory and operational challenges that electrical professionals face day to day.
We develop in close partnership with leading electrical contractors - including Darke & Taylor Ltd, a leading MEP contractor in the south-east of England - ensuring that our products are shaped by real-world design and compliance practice rather than theoretical assumptions. Our team understands BS 7671 Appendix 4, BS 7909, IET Codes of Practice, and the daily realities of managing electrical compliance across commercial, industrial and residential projects.
More tools from Construct Software
CableSpec is one part of a broader ecosystem of specialist software products. Each is independently useful - together they cover the full breadth of electrical engineering, compliance and contracting work.
CableSpec Pro
Cable design for complete distribution networks. Model boards and sub-mains, track cumulative voltage drop and produce board schedules and network diagrams.
- Project-level multi-circuit management
- Distribution board scheduling
- Cumulative voltage drop through sub-mains
- Comprehensive project calculation reports
SafetyCert
Cloud-based compliance management for MEP contractors - PAT testing, Minor Works, EICRs, document management and live compliance dashboards across sites and buildings.
- PAT testing with asset registers and session locking
- Minor Works certificates to BS 7671
- EICR tracking with C1/C2/C3/FI observations
- Multi-site compliance dashboard and expiry alerts
ElectraCert
Produce compliant Electrical Installation Certificates, Minor Works Certificates and Condition Reports to the latest wiring regulations.
- EIC, MEIWC and EICR certificate production
- Compliant with BS 7671:2018+A4:2026
- Schedule of inspections and test results
- PDF generation and client distribution
InterimReport
Interim building condition reports for any building — commercial, public and residential. Offline mobile app, GPS-stamped evidence, locked PDF reports and secure client share links.
- Template library plus fully custom templates
- Locked and timestamped PDF report output
- Secure client share link with expiry control
- Re-inspection reminder email scheduling
ContractorCompliance
Manage contractor insurances, qualifications and certifications, with a self-service portal for contractors to maintain their own credentials in real time.
- Insurance and certification expiry tracking
- Contractor self-service upload portal
- Accreditation scheme verification (NICEIC, NAPIT, ECA)
- Compliance status dashboard for procurement teams
TESCert
Purpose-built for events, media and entertainment - produces BS 7909 temporary electrical system certificates with full inspection records and PDF output.
- BS 7909 certificate production
- Inspection and test record management
- PDF certificates with digital signatures
- Designed for events and live production
Ready to use CableSpec?
Contact us to request a demonstration and we’ll walk you through the full calculation workflow. Already a Construct Software customer? Request pricing, order your licence then access CableSpec directly from the Start dashboard.