The cable sizing sequence
Every cable calculation follows the same steps. Click a step to jump to it. The status of each step for the current circuit is shown live.
The golden rule
Ib ≤ In ≤ Iz
Design current () ≤ device rating (In) ≤ cable rating after correction (). Then voltage drop, fault protection and the protective conductor must also pass.
Design current
Describe the circuit. The design current is the current the cable carries in normal service.
Derating and cable selection
Choose the protective device and installation conditions. The lab finds the smallest cable that carries the corrected current.
Current ratings used (editable)
Illustrative ratings for multicore XLPE/SWA copper cables clipped direct at 30 °C. Replace them with the values from your specified table or the manufacturer.
Voltage drop
Calculated from the conductor resistance at operating temperature and its reactance, so you can see where tabulated mV/A/m values come from.
Voltage along the circuit for each cable size
Earth fault loop impedance and adiabatic check
The protective device must disconnect a fault in time, and the protective conductor (cpc) must survive the fault energy until it does.
Lighting layout by the lumen method
Enter the room and the luminaire. The lab works out how many fittings you need, arranges them in a grid and checks the result point by point.
Layout and direct illuminance grid (lux)
The grid uses direct light only (no reflections), so it reads lower than the lumen method average. It is used here to check spacing and uniformity.
3D lit room and 4D daylight dimming
Your layout in 3D with light cones and the floor coloured by illuminance. Play the day: daylight from the window rises and falls, and daylight-linked dimming trims the fittings near the window to save energy.
Engineer's notes
Lessons from real design reviews.