Electrical calculators
Free tools for cable sizing, demand and circuit checks. No account needed.
33 calculators
Installation and sizing
Voltage drop
Check voltage drop or find a minimum conductor size with the simplified Table C8 method.
Maximum demand
Appendix C load groups, assessed phase by phase.
Internet connection requiredEarth conductor size
Look up a protective earthing conductor size from the active size and material.
Cable sizing
Compare copper V-75 sizes for current capacity, installation conditions and voltage drop.
Conduit fill
Check how much conduit space the selected cables occupy.
Power and protection
Motor full load current
Estimate motor current from its rating and supply. Confirm with the nameplate.
kW and kVA
Convert real and apparent power using power factor, with reactive power shown.
Earth fault resistance
Maximum Rphe and Re to compare with continuity tests.
Earth fault loop impedance
Maximum Zs and route length from device and cable.
DC and electronics
Series / parallel resistors
Find the combined resistance of ideal resistors in series or parallel.
Ohm's law
Enter two known values to solve voltage, current or resistance in a DC circuit.
Resistor colour code
Read a four- or five-band resistor to find its resistance and tolerance.
LED resistor
Calculate a series resistor and its power from the LED voltage and target current.
Voltage divider
Find the output voltage of an unloaded two-resistor divider.
RC time constant
Calculate the time constant from resistance and capacitance.
Series / parallel capacitors
Find the combined capacitance of ideal capacitors in series or parallel.
Engineering tools
Arc flash (educational)
Explore an empirical model. Do not use these results for equipment labels, PPE selection or energised work.
Arc flash (IEEE 1584-2018)
Explore incident energy and clearing-time inputs. Independent review is outstanding; not for certification or PPE selection.
Internet connection requiredVoltage rise (export)
Estimate voltage rise from export current and cable resistance. Confirm the site limit.
Voltage rise (multi-segment)
Import or export voltage-change screening across multiple segments. Representative impedance data; verify the selected site limit.
Internet connection requiredProspective fault level
Estimate prospective fault current from voltage and source impedance.
Short-circuit withstand
Compare cable thermal withstand with the entered fault current and clearing time.
Solar PV string voltage
Check the modelled cold string voltage against the entered inverter DC limit.
EV charger demand
Estimate charger demand from power, quantity and your chosen diversity factor.
Earth rod resistance
Estimate a single earth rod’s resistance from its dimensions and uniform soil resistivity.
RCD selection (advisory)
Review RCD type and sensitivity guidance for the entered load and installation.
Emergency lighting battery
Estimate battery capacity for the lighting load and required duration.
Motor starting voltage dip
Estimate the voltage dip during a direct-on-line motor start. Simplified screening only.
Transformer currents
Calculate ideal three-phase primary and secondary currents from kVA and voltage ratings.
Battery and UPS capacity
Estimate battery capacity from load, runtime, efficiency and depth of discharge.
Protection coordination
Compare upstream and downstream clearing times. A timing margin does not establish full selectivity.
Internet connection requiredDC cable voltage drop
Check resistive voltage drop along the outgoing and return conductors of a DC circuit.
LV network
Estimate fault level and voltage drop along a radial cable path using source and segment impedance.
Internet connection required