Breakers, fuses, fault current, grounding, and arc flash
Circuit Breaker Size Calculator
Estimate a standard MCB or MCCB current rating from load power, voltage, phase, power factor, and sizing factor.
Open calculatorCircuit Protection & Grounding
Tools for breaker, fuse, RCD and RCBO selection, fault current, grounding and loop impedance, coordination, and arc-flash screening.
9 calculatorsBreakers, fuses, fault current, grounding, and arc flash
Short Circuit Current Calculator
Estimate available transformer secondary fault current from transformer kVA, impedance, voltage, phase, and optional utility fault contribution.
Open calculatorBreakers, fuses, fault current, grounding, and arc flash
Fuse Sizing & Selection Calculator
Size a preliminary gG, aM, or gPV fuse and check load current, cable ampacity, breaking capacity, motor starting duty, or PV module limits.
Open calculatorBreakers, fuses, fault current, grounding, and arc flash
MCB Inrush Compatibility Checker
Compare equipment inrush current with IEC-style B, C, or D magnetic-trip bands and check whether available fault current supports instantaneous operation.
Open calculatorBreakers, fuses, fault current, grounding, and arc flash
RCD & RCBO Selection Calculator
Select a starting residual-current type, sensitivity, poles, rated current, overcurrent curve, and breaking capacity for common loads.
Open calculatorBreakers, fuses, fault current, grounding, and arc flash
Grounding Resistance Calculator
Estimate single vertical ground-rod resistance and a preliminary multiple-rod result from soil resistivity, rod length, diameter, count, and spacing.
Open calculatorBreakers, fuses, fault current, grounding, and arc flash
Circuit Breaker Selectivity and Cascading Checker
Screen upstream and downstream breaker rating, curve, breaking capacity, and fault-current coordination.
Open calculatorBreakers, fuses, fault current, grounding, and arc flash
Earth Fault Loop Impedance Calculator (Zs)
Calculate actual earth fault loop impedance and compare it with a device-based maximum Zs input.
Open calculatorBreakers, fuses, fault current, grounding, and arc flash
Arc Flash Incident Energy Calculator β IEEE 1584-2018
Calculate IEEE 1584-2018 arcing current, incident energy, and arc-flash boundary for normal and reduced-current clearing-time scenarios.
Open calculatorCoordinate load, trip behavior, and fault duty
Circuit protection coordinates load current, conductor capacity, overload response, instantaneous or magnetic operation, prospective fault current, breaking capacity, earth-fault path, and disconnection time.
Breakers, fuses, RCDs, RCBOs, and grounding conductors perform different functions. A complete design often requires several protection devices working together.
Protection is a coordinated system
A device rating above load current is not enough. Its trip behavior must protect the conductor, tolerate legitimate inrush, interrupt the available fault current, and coordinate with upstream and downstream devices.
Ground-fault and residual-current protection are related but not interchangeable. Loop impedance concerns fault current and automatic disconnection, while RCD or RCBO type and sensitivity concern residual-current waveform and leakage protection.
Applications
Where these calculators fit
Overcurrent selection
Screen MCB, MCCB, fuse, and motor-protection ratings from the actual load basis.
Fault and grounding checks
Estimate available fault current, loop impedance, grounding requirements, and breaking duty.
Coordination and safety
Review inrush compatibility, selectivity, cascading, and incident-energy conditions.
FAQ
What is the difference between rated current and breaking capacity?
Rated current describes continuous carrying duty. Breaking capacity describes the maximum prospective fault current the device can interrupt under specified conditions.
Can B, C, and D curves be selected from load current alone?
No. Curve selection also depends on inrush, fault current at the installation point, conductor protection, and disconnection requirements.
Does an RCD replace overcurrent protection?
Not unless it is an RCBO with integrated overcurrent protection. An RCCB or RCD normally requires coordinated upstream overcurrent protection.
Explore more
Other electrical calculator categories
Electrical Fundamentals & Circuit AnalysisCore formulas, phase power, resistance, circuits, and unitsβCable, Wire & Voltage Drop ToolsConductor size, ampacity, voltage drop, and fault withstandβCable Management & InstallationConduit, tray, glands, lugs, routing, and cable entryβPower Systems & DistributionTransformers, demand, ATS, busbars, power quality, and generatorsβPanels, Enclosures & ThermalPanel heat, terminals, clearances, creepage, and enclosure ratingsβMotors, Contactors & DrivesMotor current, starting, contactors, voltage quality, and VFDsβSolar, Battery & Backup PowerPV strings, batteries, inverters, UPS, charging, and backup energyβSurge & Lightning Protection ToolsLightning exposure, SPD selection, coordination, and backup protectionβEV Charging ToolsCharging time, cost, current, demand, and feeder planningβLighting DesignLux, lumens, fixtures, circuits, efficiency, and emergency lightingβ