AzadCircuitHub | Calculators, NEC & IEC Guides
Free Electrical Engineering Calculators and Standards-based Guides
Electrical Design Answers, Checked Against the Standards.
Size busbars, set relays, fill cable trays and earth a system with calculators built on IEC, NEC and IEEE. Then estimate your electricity bill, plan solar or EV charging, and pick the right test tools.
- Standards covered
- IEC, NEC, IEEE, BS 7671
- Prepared by
- Abdul Wassay, Electrical Engineer
- Field experience
- 15+ years, power systems and protection
- Cost
- Free to use
Everything on AzadCircuitHub, by Topic
Follow a feeder from the main bus to the topic you need. Each link opens a full hub with calculators, guides and Worked Examples.
Design & protection
- BBBusbar sizing & protectionSize, ampacity, heat rise and clearance to IEC and NEC
- 51Relay protection settingsOvercurrent, earth fault, overload and differential relays
- CTCable tray & conduit fillNEC 392 fill, bending radius and pull box sizing
- CFConduit fill calculatorMulti-standard fill for NEC, IEC, BS 7671, CSA and AS/NZS
- PEEarthing guides & toolsEarth cable sizing and testing across IEC, NEC and BS 7671
- STDElectrical standardsIEC, NEC and IEEE explained in plain language
- ΣConcepts & circuitsPower factor, demand factor, circuit theory and fault analysis
Power & energy systems
- PVSolar energySystem sizing, charge controllers, tubewell solar and insurance
- EVEV charging & e-mobilityInstallation costs, circuit sizing and charging standards
- TTransformersTesting, OCPD and neutral sizing, plus supplier lists
- MMotors & drivesOverload settings, motor cable sizing and VFD connections
- GGenerators & backup powerGenerator sizing, fuel consumption and maintenance
Bills, reviews & business
- USUS electricity bill calculatorsUtility-specific estimators for PG&E, Con Edison, FPL, ComEd and more
- PKPakistan DISCO bill calculatorsLESCO, GEPCO, FESCO, K-Electric and every other DISCO
- REVProduct reviewsMultimeters, clamp meters, voltage testers and thermal cameras
- L2EV charger reviewsLevel 2 charger comparisons by vehicle, budget and install type
- INSElectrical insurance & costsElectrician, contractor and solar panel coverage guides
Not sure where to start? Browse every calculator in one place.
Browse all calculatorsLatest Guides and Reviews
Newly published engineering explainers on one side, tool reviews and buying guides on the other. This list updates itself whenever you publish.
Engineering Guides
- Busbar Zone Protection: Check Zone vs Discriminating Zone
- IEC 61439 Temperature Rise Limits for Busbars
- Factors Affecting Busbar Current Carrying Capacity
- Common Busbar Sizing Mistakes to Avoid
- Earth Cable Sizing: NEC vs. IEC vs. BS 7671 vs. IEEE 80 Compared
Tool Reviews & Buying Guides
- Renogy Rover 40A MPPT Review: Features, Performance & Buying Guide
- Fluke 117 for HVAC Technicians: Complete Review and Buying Guide
- Klein ET310 Circuit Breaker Finder Review: Features, Testing & Buying Guide
- FLIR ONE Pro Review: 480×360 Thermal Imaging Camera for Electrical Inspection
- Raylix Level 1&2 EV Charger Review: Best Budget Option?
Some reviews contain affiliate links. As an Amazon Associate I earn from qualifying purchases, at no extra cost to you. See the affiliate disclosure.
Design / Protection Guides & Tools
The core engineering toolkits: busbars, cable tray and conduit, and earthing. Each panel lists the calculators first, then the guides that explain the standards behind them.
Busbar sizing & protection
Size copper and aluminium busbars, check heat rise and protection, and verify clearances to IEC and NEC.
Calculators
- Busbar sizeSizing to IEC and NEC
- Current carrying capacityCross-section, ambient and installation
- Heat capacityThermal rise under load and fault
- Busbar protectionThermal withstand and peak making current
- Phase-to-phase clearanceIEC 61439 switchgear and panels
Guides
Cable tray & conduit fill
Code-cited fill calculations for trays and conduit, plus bending radius and box-sizing guidance.
Calculators
Guides
Electrical earthing
Earthing from first principles to standards-specific conductor sizing, so you can design, size and verify a system correctly.
Calculators
- Earth cable sizeResidential to industrial and solar
- Earth cable size, AustraliaAS/NZS 3000 requirements
- Earth cable size, solar panelsDC-side and AC-side earthing
Guides
Also in Design and Protection
Relay protection settings
Electrical standards
- What is an IEC standard?Complete beginner's guide
- Top 10 IEC standardsEvery engineer should know
- IEC 61000EMC standards guide
- IEEE short circuitCalculation standard
- IEEE hipot testingComplete test guide
- IEEE megger testingInsulation resistance
- IEC vs IEEEComparative guide
- Standards libraryAll IEC, NEC and IEEE guides
Estimate your Electricity Bill by Utility
Every estimator follows that utility's real tiers, time-of-use and seasonal rates instead of a national average. Pick your provider.
No utility matches that search. Browse the full lists instead: US utilities or Pakistan DISCOs.
United States
Midwest & Central
Other regions
Find the Right Home EV Charger
Level 2 charger comparisons that weigh charging speed, smart features, weatherproofing and what your home's wiring can support.
Best Level 2 EV Charger: top 7 picks
Our full comparison covering charging speed, smart features and pricing across the leading models.
Compare the top 7Individual in-depth reviews
Shopping for a vehicle?
Check your home before you buy
As an Amazon Associate I earn from qualifying purchases. This series contains affiliate links, so I may earn a commission if you buy through them, at no extra cost to you. See the affiliate disclosure.
Plan a Solar System from Array to Insurance
Follow the chain in order. Each step opens the calculator or buying guide for that part of the system.
- CalculatorSize the arrayMatch panel capacity to your daily load
- CalculatorSize the inverterMatch the inverter rating to your loads and array
- Buying guidePick a charge controllerMPPT vs PWM, with top picks
- Buying guideChoose a kitComplete home, off-grid and grid-tie setups
- CalculatorSize the DC cablesSolar, battery and off-grid runs
- GuideEarth the systemDC-side and AC-side conductor sizes
- CalculatorInsure itEstimate your solar panel premium
Sizing a pump? The agricultural calculator sizes solar for tubewell systems.
Power Equipment Guides & Tools
Transformers, motors and generators: sizing and protection tools first, then the testing, supplier and standards guides behind them.
Transformers
Transformer sizing, protection and testing, plus manufacturer and supplier directories.
Sizing & protection
- Transformer OCPD sizingBreaker and fuse selection per NEC
- Transformer neutral sizingConductor selection and compliance
- Protection schemesTypes and application guide
- Differential relay settingsTransformer and busbar schemes
Testing & suppliers
Motors & drives
Size, connect and protect motors, from overload settings to cable sizing and VFD connections.
Sizing & protection
- Motor overload setting tablePDF and Excel download
- Size motor overload protectionStep-by-step guide
- Wire sizing for motorsMotor cable size calculation
- Overload relay settingsNEC 430.32 and IEC 60947-4-1
Drives & applications
Generators & backup power
Size generators, estimate fuel and load, and learn protection and excitation for backup and plant machines.
Calculators
- Generator sizingResidential and commercial diesel
- Generator power consumptionFuel and load usage estimate
- Generac generator sizeFind the right size
Protection & testing
Learn, Insure and Buy
The theory behind the calculators, insurance costs for electricians and solar owners, and the test tools worth putting in your kit.
Concepts & circuits
The fundamentals that make the calculators make sense.
Calculator
Guides
Insurance & contractor costs
Coverage types, typical costs and what to compare when insuring an electrical business or solar panels.
Calculator
Guides
Tool buying guides
Researched comparisons of the meters and testers electricians rely on, judged on safety ratings, specs and value.
Roundups
- Best Multimeter for Electricians: Top 7
- Best Multimeter for Homeowners
- Best Clamp Meter for Electricians
- Best 10 Voltage Testers for Electricians
- Best Non-Contact Voltage Tester
- Best Thermal Imaging Camera for Electricians
- 5 Best Wire Strippers for Electricians
- Top 20 Electrical Testing Tools You Must Have
As an Amazon Associate I earn from qualifying purchases. Some guides contain affiliate links, so I may earn a commission if you buy through them, at no extra cost to you. See the affiliate disclosure.
Built by a Working Electrical Engineer
Every calculator and guide on AzadCircuitHub is written and checked by an engineer who has done this work in the field.
Abdul Wassay
Founder and Lead Author
Electrical engineer with 15+ years in power systems, protection and control, industrial automation, PLC/SCADA, and renewable energy EPC projects.
How Every Tool and Guide is Built
- Built on the standard, not a rule of thumbEach calculator is written against a published standard, such as IEC 61439, NEC 392 or IEC 60255, and names it on the page.
- Explained, not just answeredGuides show the working and worked examples, so you understand why the number is what it is.
- Open about moneyReviews are researched and compared, and affiliate links are always disclosed. Read the affiliate disclosure.
Frequently Asked Questions
Quick answers about the tools, the standards behind them and how to use them well.
Are the calculators free to use?
Yes. The calculators and guides are free to use. The site is supported by advertising and affiliate links in product reviews, which are disclosed on every page where they appear.
Which standards do the calculators follow?
Calculators are built on IEC, NEC and IEEE, plus BS 7671 and regional codes such as AS/NZS 3000 where it matters. Each tool names the standard it applies, so you can check the clause yourself. Start with the full calculator library.
How do you size a busbar according to IEC 61439?
Busbar sizing under IEC 61439 considers current-carrying capacity, ambient temperature, enclosure type and short-circuit withstand. The Busbar Size Calculator applies these factors for copper and aluminium bars.
What is the difference between an overload relay and an earth fault relay?
An overload relay protects against sustained excess current in a circuit or motor. An earth fault relay detects current leaking to earth, which usually points to insulation failure or a safety hazard. Try the Overload Relay and Earth Fault Relay setting calculators.
What is the fill limit for a cable tray under NEC 392?
NEC 392 sets maximum fill by tray type, tray width and cable size, so the limit is not one fixed percentage. The Cable Tray Fill Calculator checks your cables against it, and the fill chart shows the maximum by tray width.
How accurate are the electricity bill calculators?
They are estimates built from each utility's published rates, tiers and charges. Your actual bill can differ because of fuel adjustments, taxes, meter reading dates and rate changes. Pick your provider in the US utility or Pakistan DISCO lists.
Can I rely on a calculator for a real installation?
Use the results to check and speed up your design, not to replace it. Final designs should be reviewed by a qualified engineer or electrician and checked against local code and the authority having jurisdiction.
Spotted an error or want a new calculator?
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