Electrical Calculators

Cables & containment

• Adiabatic Cable Check CalculatorCheck an earth conductor will survive a fault undamaged.
• Cable Derating / Correction Factors CalculatorAdjust a cable's current rating for how it is installed.
• Cable Sizing CalculatorFind the right cable size for a circuit.
• Containment Fill CalculatorCheck how full a tray, trunking or conduit will be.
• Earthing & Bonding Conductor Sizing CalculatorSize earthing and bonding conductors for an installation.
• Electrical Voltage Drop CalculatorCheck the voltage drop on a cable run is within limits.

Protection & fault current

• Earth Fault Loop Impedance (Zs) CalculatorCheck a fault will trip the protective device quickly enough.
• Motor Starting Current CalculatorFind a motor's starting current and the voltage dip it causes.
• Short Circuit Fault Current CalculatorEstimate the fault current a circuit has to withstand.

Supply, demand & power quality

• Battery Storage Sizing CalculatorSize a battery to store solar power, with savings and payback.
• EV Charger Load & Demand CalculatorFind the supply current a bank of EV chargers needs.
• Generator / Standby Set Sizing CalculatorSize a standby generator for the loads it has to carry.
• Maximum Demand CalculatorApply diversity to connected loads to find the real demand.
• Power Factor Correction CalculatorSize capacitors to improve power factor and cut demand charges.
• Three-Phase Power Converter CalculatorConvert between kW, kVA and kVAr on a three phase supply.
• Transformer FLC & PSCC CalculatorFind a transformer's full load current and fault current.

Lighting & life safety

• Emergency Lighting Battery & Duration Check CalculatorSize a central battery for emergency lighting.
• Fire Alarm Standby Battery Sizing CalculatorSize the standby batteries for a fire alarm panel.
• Lighting Lumen Method CalculatorWork out how many light fittings a room needs.

About these electrical calculators

The electrical set covers the checks that decide whether a circuit design stands up: conductor size, volt drop, disconnection, fault withstand and the demand the installation actually presents.

Nearly all of them are worked to BS 7671:2018+A2:2022 and cite the regulation or table they rely on - the adiabatic check uses Regulation 543.1.3 with k values from Tables 54.2 and 54.3, cable sizing and derating use the Appendix 4 rating and correction factors, and earth fault loop impedance is checked against the maximum Zs for the protective device. Beyond the Wiring Regulations, transformer sizing follows IEC 60076-1, lighting design references BS EN 12464-1, fire alarm work BS 5839-1, and the renewables calculators use MCS methodology.

They are built for electricians, electrical designers and inspectors who need a quick, checkable answer during design or verification - not a black box that returns a number with no working.

Each shows the equation and the values it selected, so you can confirm it picked the right table before you rely on the result. They support a design; they do not replace one.

Frequently asked questions

Which edition of BS 7671 do these follow?

BS 7671:2018+A2:2022 - the 18th Edition incorporating Amendment 2. Where a calculator reads from a table, the table number is shown on the page so you can verify it against your copy of the Regulations.

Does the cable sizing calculator handle grouping and ambient temperature?

Yes. Derating applies the Appendix 4 correction factors for ambient temperature, grouping and thermal insulation, and the calculator shows each factor it applied rather than only the final corrected rating.

Is this enough to certify an installation?

No. These check individual design criteria - current-carrying capacity, volt drop, fault withstand, disconnection time. Certification requires inspection and testing by a competent person under Part 6 of BS 7671.

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