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Free Electrical Calculator Tools

Professional-grade electrical calculators for UK electricians. Built around current BS 7671 references. No signup, no email, just tools that work.

Exam Prep
2391-52 Mock Exam
Timed 60-question City & Guilds inspection and testing mock exam with answers and explanations after submission.
  • 120-minute timer
  • 60 MCQ questions
  • Post-submit explanations
  • Outcome breakdown
Most Popular
Max Zs Calculator
Calculate maximum earth fault loop impedance instantly. BS 7671 tables for BS EN 60898, BS 3871, and fuses.
  • BS 7671:2018+A4:2026 references
  • BS 3871 legacy breakers
  • Fuses included
  • Table references shown
Pro Grade
Voltage Drop & SWA Cable Size Calculator
Calculate UK voltage drop and cable sizes with SWA gland sizing. Supports adiabatic equation checks.
  • Volt drop calculation
  • Voltage drop calculator UK
  • SWA gland sizing
  • Adiabatic check
Smart Engine
Observation Builder
Describe a fault and get the correct C1/C2/C3 code with BS 7671 regulation references.
  • 3 free lookups daily
  • Regulation references
  • Professional wording
For Businesses
Maximum Demand Calculator
Calculate maximum demand with diversity factors. Supports multiple distribution boards and circuit types.
  • Multiple DB support
  • Diversity factors
  • Circuit type presets
  • Export results
Testing
R1+R2 & Ring Continuity Calculator
Calculate expected R1+R2 from r1 and r2 readings. Review ring continuity guidance and estimate ring length.
  • R1+R2 calculation
  • r1, rn, r2 validation
  • Ring length estimate
  • Balance checking
  • Spur guidance
Reg 612.11
PFC Calculator
Calculate prospective fault current (PSCC & PEFC). Verify protective device breaking capacity.
  • PEFC & PSCC calculation
  • Breaking capacity check
  • Supply type presets
  • Ipf determination

Download the Max Zs Cheat Sheet

Get the complete BS 7671 Max Zs tables as a printable PDF. Free, no email required.

Download PDF
About These Free Electrical Tools
Electrical calculators built around current UK wiring regulation references

2391-52 Mock Exam

Practise the City & Guilds 2391-052 online test with a free timed 60-question mock exam. Answers, explanations, and learning outcome breakdowns are shown after submission.

Max Zs Calculator

Quickly determine maximum earth fault loop impedance. Includes values from Table 41.2, 41.3, and 41.4 of BS 7671, covering Type B, C, and D MCBs, BS 3871 legacy breakers, and common fuse standards.

Voltage Drop & Cable Size Calculator

Select the correct cable for your installation with a UK voltage drop calculator. Considers current carrying capacity, mV/A/m volt drop, SWA gland sizing, and adiabatic checks for protective conductor sizing.

Observation Builder

Classify observations correctly. Describe the fault and get the appropriate C1, C2, C3, or FI code with BS 7671 regulation references.

Maximum Demand Calculator

Assess load requirements with diversity factors per BS 7671. Supports multiple distribution boards for complex commercial installations.

R1+R2 & Ring Continuity Calculator

Calculate expected R1+R2 for ring final circuits using (r1 + r2) ÷ 4. Checks r1, rn, r2 balance, detects broken rings, unbalanced conductors, and spurs with fault classification.

PFC Calculator

Calculate prospective fault current from impedance values. Determines PSCC and PEFC to verify protective device breaking capacity per Regulation 612.11.

Ready for the Full Experience?

These free tools are just a taste. TestFast automates your entire EICR workflow with the observation builder, handwriting & consumer unit OCR, and instant certificate generation.

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