Electrical
A working V·I·P·R calculator and a load calculator electrical reference for the standards that govern electrical design — NEC (US), IEC 60364 (Europe), AS/NZS 3000 (Australia / NZ). Covers AC and DC, single-phase and three-phase, residential through industrial — including electrical loading calculator workflows, sizing electrical cable calculator (also written electrical cable size calculator or wire sizing electrical) lookups, and the calculator for electrical load demand-factor logic per NEC 220. Reviewed by a licensed PE.
Use the electrical calculator
Pick phase mode and which two of {V, I, P, R} you have — the calculator returns the rest plus apparent power, reactive power, HP, and BTU/hour equivalents.
Pure DC: P = V · I. Resistance shown is V/I (Ohm's law equivalent).
- Apparent power S
- — kVA
- Reactive power Q
- — kVAR
- Power factor used
- —
- Mechanical equivalent
- — HP
- Heat output
- — BTU/hr
P = V · I = ... The electrical formulas
Three formulas cover the bulk of electrical design work — Ohm\'s Law for component-level analysis, the power equation for system sizing, and the impedance relation for AC behaviour.
- V
- voltage, V
- I
- current, A
- R
- resistance, Ω
- P
- power, W
- cos φ
- power factor (1.0 for resistive), —
- V_LL
- line-to-line voltage (3-phase), V
- Z
- impedance magnitude, Ω
- R
- resistance (in-phase opposition), Ω
- X
- reactance (90° out-of-phase opposition), Ω
Worked example: residential 200 A service
A 1800 sq ft single-family house with electric range, dryer, water heater, and HVAC. Compute the service amperage per NEC 220.
| Load | Calc | VA |
|---|---|---|
| General lighting (3 VA × sq ft) | 1800 × 3 | 5400 |
| Small-appliance circuits (2 × 1500) | 3000 | 3000 |
| Laundry circuit | 1 × 1500 | 1500 |
| General + small appliance subtotal | 9900 | |
| Demand factor: 100% of first 3000, 35% of remainder | 3000 + (9900−3000) × 0.35 | 5415 |
| Range (8 kW + demand factor) | NEC Table 220.55 | 8000 |
| Dryer (5 kW) | nameplate | 5000 |
| Water heater (4.5 kW × 1.0) | continuous | 4500 |
| HVAC (largest of heat or cool, 5 kW) | NEC 220.82 | 5000 |
| Total demand | 27 915 VA | |
| Service amps (240 V single-phase) | 27 915 / 240 | 116 A |
| Standard service size | round up | 125 or 150 A (200 A typical for future EV charging) |
How to do an electrical load calculation, step by step
- Identify the system: AC or DC, voltage class, phase configuration. Residential mains: 120 V or 240 V single-phase (US), 230 V single-phase (EU), 400 V three-phase (industrial). Battery / solar: DC at 12 / 24 / 48 V or higher. Industrial: 480 V three-phase (US), 400 V (EU).
- List all connected loads with their nameplate ratings. Each load: nameplate watts, volts, amps, power factor (if AC). Distinguish continuous loads (3+ hours at full current — most lighting, HVAC, motors) from non-continuous.
- Sum the loads with the appropriate demand factor. Per NEC 220, residential general lighting uses 3 W per square foot; small-appliance circuits get 1500 VA each. Commercial uses tabulated demand factors that allow for diversity (not everything runs at once).
- Compute the service amperage. I = total VA / (V × √3 for 3-phase). Apply the 1.25× continuous-load multiplier per NEC 210.19/215.2/230.42. Round up to the next standard service size: 100 / 200 / 400 A residential.
- Pick the conductor that satisfies both ampacity and voltage drop. NEC 310.16 ampacity table with derating for ambient and conductor count. NEC informational note 210.19(A): keep voltage drop ≤ 3% on branch, 5% combined. See Wire Size Calculator.
- Pick the breaker per NEC 240.6(A) standard sizes. Smallest standard size ≥ continuous load × 1.25 + non-continuous. Verify breaker AIC ≥ available short-circuit current at that point — see Short Circuit Calculator.
- Document and stamp. In jurisdictions requiring permitted electrical work, the design must be drawn, calculated, and signed by a licensed PE before installation. Keep all calculations on file for inspection and future modification.
Standards and codes
Three standards govern most electrical installation worldwide. Each follows similar physics but differs in details — wire sizes (AWG vs mm²), voltage levels, derating factors.
NEC (USA)
The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. This Code is not intended as a design specification or instruction manual for untrained persons.
IEC 60364 (International)
The IEC 60364 series covers low-voltage electrical installations (≤1000 V AC). Adopted by most European countries with national variations. Key parts: 60364-4-41 (protection against electric shock), 60364-5-52 (wiring systems), 60364-5-54 (earthing arrangements).
AS/NZS 3000 (Australia / New Zealand)
Australia / NZ "Wiring Rules" — independent of NEC but aligned with IEC. Covers selection of cables (AS/NZS 3008), earthing, RCDs, voltage classifications. Mandatory installation standard in both countries.
IEEE C2 (NESC — National Electrical Safety Code)
Governs utility transmission and distribution systems above 1000 V — the regime above where NEC stops. Used by all US electric utilities for outdoor primary lines.
Electrical: comparison and differences
| Term | What it means | Typical use |
|---|---|---|
| Electrical engineering | Power generation, transmission, distribution, motors | Utilities, industrial, building services |
| Electronics engineering | Low-power signal processing with semiconductors | Computers, communications, sensors |
| Electromagnetic engineering | Fields, antennas, propagation | RF, radar, microwave, motors design |
| Power engineering | Subset of EE specialising in bulk power | Utility planning, generation, transmission |
| Building services / MEP | Electrical, mechanical, plumbing in buildings | Commercial / residential design and code compliance |
Variants and special cases
AC vs DC electrical systems
AC dominates utility distribution because it transforms efficiently to high voltage for low-loss transmission. DC dominates batteries, electronics, EVs, and HVDC long-distance links. Most modern grids are AC end-to-end with DC interties.
Single-phase vs three-phase
Single-phase: residential service, small commercial. Three-phase: most commercial and all industrial — smoother power flow, smaller motor windings for the same kW.
Residential electrical service
Standard US: 120/240 V split-phase, 100 A or 200 A. Standard EU: 230 V single-phase, 32–63 A typical. Standard AU/NZ: 230 V single or 400 V three-phase.
Commercial electrical service
208/120 V three-phase wye, or 480/277 V three-phase wye in US. Service sizes from 200 A (small office) to thousands of amps (data centres). 400/230 V three-phase in EU/AU.
Industrial electrical service
480 V three-phase US, 400 V three-phase EU, 600 V Canada. Large industrial uses primary 13.8 kV or 25 kV stepped down on-site.
Electrical safety and arc flash
NFPA 70E (US) and equivalent international standards govern PPE, approach boundaries, and arc-flash incident energy. Working on energised equipment requires arc-rated clothing, voltage gloves, and a written safety plan.
Electrical engineering specialisations
Power, control, electronics, communications, computer engineering, photonics — all branch from common foundation in circuits and electromagnetics. Most field practice is power and controls (industrial, utilities, building services).
Electrical quick reference
| Topic / question | Quick answer |
|---|---|
| Calculator for electrical load / electrical loading calculator | Use the NEC 220 demand-factor procedure: sum lighting (3 VA / sq ft residential), small-appliance branches (1 500 VA each), fixed-appliance nameplates, and the largest motor at 125 %. Apply the Table 220.42 demand factors and round up to a 100 / 200 / 400 A standard service. |
| Wire sizing electrical / electrical cable size calculator / sizing electrical cable calculator / electrical cable sizing calculator / electrical cable ampacity | Pick the smallest AWG (or mm²) that satisfies both NEC 310.16 ampacity and the ≤ 3 % branch / ≤ 5 % combined voltage drop limit, after derating for ambient temperature and conductor count. The wire size calculator automates the whole check. |
| What is arcing electrical | An electrical arc is a sustained discharge through ionised air, formed when a switch opens under load or two energised conductors part. NFPA 70E (2024) governs arc-flash hazard analysis, PPE, and approach boundaries. |
| What is VAC electrical / VAC electrical / AC meaning electrical / a c meaning electrical / ac dc electrical meaning | VAC = "volts alternating current"; the suffix distinguishes AC values from DC (VDC). On a "120 VAC, 60 Hz" nameplate the device runs on standard US mains. AC means alternating current — polarity reverses 50 or 60 times per second; DC means direct current — constant polarity. |
| Electrical neutral vs ground | The neutral conductor carries return current under normal load and is bonded to ground only at the service entrance. The ground (equipment grounding conductor) carries no normal current — it provides a fault-clearing path. NEC 250 governs grounding and bonding. |
| Electrical circuit examples | A residential 15 A lighting branch is the simplest example: 14 AWG copper, 15 A breaker, 120 V load, neutral and ground returning to the panel. Three-phase examples include 480 V motor branches, 277 V lighting feeders, and 480 V VFD-fed pump circuits. |
| Exposed electrical wiring / orange wire electrical | Exposed electrical wiring is a code violation in NEC and IEC residential settings — conductors must be in a raceway, cable assembly, or enclosure unless explicitly allowed. The orange wire on US house wiring is the ungrounded "B" or "high leg" of a 120 / 240 V four-wire delta service (NEC 110.15 requires orange marking). |
| Electrical net | "Electrical net" usually means the electrical network or grid — the synchronised set of generators, transmission lines, and substations that delivers power to end users. The North American grid runs as Eastern, Western, and ERCOT (Texas) interconnections. |
| Famous electrical engineer / electrical engineer famous / well known electrical engineers / electrical scientist | Notable electrical engineers and scientists: Nikola Tesla (AC induction motor), Thomas Edison (incandescent lamp, DC distribution), Charles Steinmetz (AC theory), Alessandro Volta (battery), Michael Faraday (electromagnetic induction), James Clerk Maxwell (electromagnetic theory), Heinrich Hertz (radio waves), Lee de Forest (vacuum-tube triode), Claude Shannon (information theory), Jack Kilby (integrated circuit). |
| Industrial electrical cord | Industrial electrical cord (NEC 400.4 cord types — SO, SOOW, SJ, SJOOW, etc.) is rated for portable equipment, temporary wiring, and pendant drops. Heavier insulation than residential SPT/SVT zip cord, and oil / weather resistance designators baked into the type letters. |
| Electrical power system analysis software | Industry-standard packages: ETAP, SKM PowerTools, EasyPower, DIgSILENT PowerFactory, PSS®E, OpenDSS (open-source). They run load flow, short-circuit, arc-flash, and motor-starting studies feeding the electrical calculation deliverables required for utility approval. |
| Power calculator electrical / electrical calculation | The power calculator electrical use cases are covered by the power calculator above and the short-circuit, voltage drop, and wire size sister pages. All run on the same V·I·P·R foundation. |
| C & J electrical / J electrical / J & J electrical | Common contractor company-name patterns ("C&J Electrical", "J Electrical", "J&J Electrical") — search results land here when users look up a local electrical contractor; not a topic of this engineering reference. |
Related concepts on this site
Frequently asked questions
- How is electrical power calculated?
- Three forms covering all common cases. DC: P = V × I. Single-phase AC: P = V × I × cos φ (active power, kW). Three-phase AC: P = √3 × VLL × I × cos φ. The cos φ correction (power factor) accounts for current that does no real work because it flows in and out of inductive or capacitive components without dissipating energy. Use the calculator above with the right phase mode.
- What is arcing in electrical?
- An arc is a sustained electrical discharge through ionised air or another dielectric, formed when a switch opens under load or two conductors break apart while current is flowing. Arcs concentrate immense energy in a tiny volume — temperatures reach 19 000 °C, faster than the surface of the sun. Arc flash events can vaporise copper, eject molten metal, and produce blast pressure waves that injure or kill workers. NFPA 70E (2024) governs arc-flash hazard analysis, PPE requirements, and approach boundaries.
- What is VAC in electrical?
- VAC = Volts Alternating Current. Notation used to make explicit that a voltage value is AC RMS, distinguishing from VDC (Volts DC). On equipment nameplates: "120 VAC, 60 Hz" means the device runs on 120 V AC mains at 60 Hz; "24 VDC" means it needs a 24 V battery or DC supply. Important when the same number could mean either — e.g. "12V" alone is ambiguous, "12 VDC" or "12 VAC" is unambiguous.
- What is the SI unit of electrical resistance?
- The ohm (Ω), named after Georg Ohm. One ohm is the resistance through which one volt produces one ampere of current (1 Ω = 1 V / 1 A). Defined in SI as kg·m²·s⁻³·A⁻². Common scales: milliohm (mΩ, used for cable / contact resistance), ohm (Ω, ordinary components), kilohm (kΩ, signal-level resistors), megohm (MΩ, insulation resistance). Insulation testers ("megger") read in megohms.
- How does an electrical circuit work?
- A circuit is a closed loop of conductors with a power source (battery, generator) and one or more loads. Voltage from the source pushes current through the loop; loads convert electrical energy to heat / light / motion / chemistry. Three things must be true for current to flow: closed loop, voltage source, and load (or short). Open the loop anywhere — switch off, broken wire — and current stops. Open-circuit voltage exists; only current requires a complete path.
- How to electrical load calculation?
- A load calculator electrical workflow follows NEC 220 for North America. Residential: general lighting load = 3 VA × sq ft, plus 1 500 VA per small-appliance / laundry branch, plus nameplate of fixed appliances (largest motor at 125 %). Apply demand factors from Table 220.42 (100 % of first 3 kVA, 35 % of next 117 kVA). Commercial: use Tables 220.12, 220.42, 220.55 for specific occupancies. Result is the calculated service amperage; round up to standard 100 / 200 / 400 A.
- How to calculate electrical cable size?
- Two checks must both pass. Ampacity: conductor must carry the load × continuous factor (1.25 if applicable) after derating for ambient temperature and conductor count, per NEC 310.16. Voltage drop: ≤3% branch, ≤5% combined per NEC informational note 210.19(A). Pick the smallest AWG that satisfies both. Use the Wire Size Calculator for an automated walk through both tests with NEC compliance check.
- How to trace a dead electrical circuit?
- Standard procedure: (1) verify the circuit is actually dead with a known-good multimeter (don't trust just one tester). (2) Check the breaker first — most "dead circuits" are tripped breakers in the electrical panel. (3) Test continuity from breaker to outlet, walking the circuit. (4) Use a non-contact voltage tester to find the break point upstream of the dead section. (5) For multi-wire branch circuits, check the shared neutral — open neutrals cause intermittent failures. Always lock-out / tag-out per OSHA 1910.147 before opening any device.
Sources and methodology
- NFPA. National Electrical Code (NEC) NFPA 70, 2023 Edition.
- NFPA. NFPA 70E — Standard for Electrical Safety in the Workplace, 2024 Edition.
- IEC. IEC 60364 series — Low-voltage electrical installations, multiple parts.
- Standards Australia / NZ. AS/NZS 3000:2018 — Electrical installations (Wiring Rules).
- IEEE. IEEE C2 — National Electrical Safety Code (NESC), 2023.
- OSHA. 29 CFR 1910.147 — The control of hazardous energy (lockout / tagout).