kVA to Amps Conversion Guide

Introduction

The kVA to amps calculator helps engineers convert apparent power to current for electrical system design. Our free kVA to amps conversion tool supports both single-phase and three-phase systems. Transformers, generators, and UPS systems display their capacity in kVA, but cables, breakers, and busbars must be sized for current in amperes.

Why This Conversion Matters

When a project specifies a 500 kVA transformer, the immediate engineering question is: what cable size feeds it, and what breaker protects it? The answer requires converting that kVA rating to amperes—specifically, 722A at 400V three-phase. Miss this conversion, and you risk undersized cables that overheat, undersized breakers that trip nuisance faults, or oversized infrastructure that wastes capital. Every major electrical component selection—from the main distribution panel to branch circuit conductors—depends on accurate kVA-to-amp conversion.

The Fundamental Challenge

The relationship between kVA and amperes depends entirely on voltage, and three-phase systems add the $\sqrt{3}$ factor that catches many engineers off guard. A 100 kVA load draws 144A at 400V but 277A at 208V—nearly double the current at the lower voltage. Single-phase calculations differ from three-phase calculations. This guide systematically addresses voltage levels, phase configurations, and the critical safety factors required by IEC 60364-5-52 for proper cable sizing.

What You'll Learn

This guide provides the complete methodology for kVA-to-amp conversions across all electrical configurations. You'll master the formulas for single-phase and three-phase systems with proper voltage selection per IEC 60038 standards. Practical examples demonstrate cable sizing with temperature correction, grouping factors, and voltage drop verification. Reference tables provide quick multipliers for common voltage levels and standard transformer current ratings.

Quick Answer: How to Convert kVA to Amps

Convert apparent power (kVA) to current (amps) by dividing kVA by voltage. For three-phase systems, also divide by $\sqrt{3}$.

Conversion Formulas

Where:

• $I$ = Current (A)
• kVA = Apparent power (kilovolt-amperes)
• $V$ = Potential (V)

Quick Reference

Worked Example

Reference Table

Key Standards

• 480V 3-phase: $\text{kVA} \times 1.20 = \text{Amps} (100 \text{ kVA} \times 1.20 = 120 \text{ A})$
• 208V 3-phase: $\text{kVA} \times 2.77 = \text{Amps} (100 \text{ kVA} \times 2.77 = 277 \text{ A})$
• 230V single-phase: $\text{kVA} \times 4.35 = \text{Amps} (10 \text{ kVA} \times 4.35 = 43.5 \text{ A})$

Common transformer currents at 400V 3-phase:

• 100 kVA → 144A → 70mm² cable
• 250 kVA → 361A → 185mm² cable
• 500 kVA → 722A → $2 \times 240 \text{ mm}^2$ cable
• 1000 kVA → 1443A → $3 \times 300 \text{ mm}^2$ conductor or busbar
• 1600 kVA → 2310A → Busbar mechanism

Electrical line sizing safety factors (IEC 60364-5-52):

• Continuous load ($\geq 3$h): Multiply by 1.25
• Temperature (35°C): Divide by 0.94
• Grouping (4 cables): Divide by 0.80
• Combined: Amp $\times \frac{1.25}{0.94 \times 0.80} \approx$ Electric current $\times$ 1.66

Example: 500 kVA transformer wiring sizing:

1. Full load: 722 A
2. With safety factors: $722 \times 1.66 = 1{,}199$ A required
3. Lead: $2 \times 400 \text{ mm}^2$ per phase ($2 \times 480 \text{ A}$ after derating = 720A actual)
4. Volt level drop limit: 3% = 12V at 400V

Critical rules:

• Always use $\sqrt{3}$ (1.732) for 3-phase calculations
• Use line-to-line potential (phase-to-phase), not line-to-neutral
• Apply 125% factor for continuous loads
• Verify electrical potential drop $\leq$ 3% for feeders

Standards Reference

Understanding Current Calculation from kVA

Amperage (I) measured in amperes (A) represents the flow of electric charge through a conductor. Converting from kVA to amps is essential for lead sizing, protection device selection, and electrical load analysis.

Why Convert kVA to Amps?

Electrical Equipment Ratings:

• Transformers are rated in kVA
• Generators are rated in kVA or kW
• Cables are rated by electrical flow-carrying capacity (amps)
• Circuit breakers are rated by amp (amps)

Design Requirements:

• Wire sizing requires knowing electric current flow
• Overcurrent protection must be based on I value
• Volt level drop calculations need amperage values
• Thermal analysis of conductors uses electrical flow

Relationship to Power and Voltage:

The fundamental relationship is based on the definition of apparent energy:

Single-Phase Conversion

For single-phase systems, electric current is calculated by dividing apparent electrical power by potential.

Formula Derivation:

Starting from the wattage equation:

Solving for I value:

Converting kVA to VA:

Example Calculation:

Given:

• Apparent load: S = 10 kVA
• Electrical potential: V = 230V (single-phase)

Solution:

Application: For this 10 kVA load at 230V, you would need:

• Minimum electrical line size: 10 mm² copper (IEC 60364-5-52, Table B.52-3, 50A rating)
• Circuit breaker: 50A Type C (allowing for inrush currents)
• V value drop budget: Max 3% = 6.9V over wiring length

Three-Phase Conversion

For three-phase systems, there are two methods depending on electric tension measurement type.

Method 1: Line-to-Line Voltage (Most Common)

Formula:

Where:

• $I$ = Phase amperage in amperes
• $S$ = Apparent capacity in kilovolt-amperes
• $V_{\text{L-L}}$ = Line-to-line volt level (between any two phases)
• $\sqrt{3} \approx$ 1.732

Example:

• $S$ = 100 kVA
• $V_{\text{L-L}}$ = 400V

Method 2: Line-to-Neutral Voltage

Formula:

Example:

• $S$ = 100 kVA
• $V_{\text{L-N}} = 230 \text{ V} \quad (400 \text{ V} \div \sqrt{3})$

(Small difference due to rounding of $\sqrt{3}$)

Standard Three-Phase Voltages:

Line-to-Line vs Line-to-Neutral

Line-to-Line (L-L) - MOST COMMON

When to Use:

• Balanced three-phase loads (motors, transformers)
• Delta-connected equipment
• Standard equipment nameplates (e.g., "400V 3-phase")

Measurement:

• Potential between any two phase conductors
• Use with $\sqrt{3}$ formula

Line-to-Neutral (L-N)

When to Use:

• Wye (star) connected loads with neutral
• Single-phase loads on three-phase equipment
• Lighting circuits on commercial systems

Measurement:

• Electrical potential between one phase and neutral
• Use with factor of 3 formula

Voltage Relationship:

For a balanced wye infrastructure:

Example: If $V_{\text{L-N}} = 230V, \text{ then } V_{\text{L-L}}$ = 230 $\times 1.732 = 398V \approx$ 400V

Worked Example: cable sizing

Scenario: Size cables for a 500 kVA, 400V three-phase transformer secondary.

Step 1: Calculate Full Load Current

Using L-L formula:

Step 2: Apply Continuous Load Factor (125%)

Per IEC 60364-5-52, for continuous loads ($\geq$ 3 hours):

Step 3: Apply Temperature Correction

Ambient degree 35°C, correction factor = 0.94:

Step 4: Apply Grouping Factor

4 cables in conduit, grouping factor = 0.80:

Step 5: Select Cable Size

From IEC 60364-5-52, Table B.52-3 (copper, XLPE, 70°C):

• 240 mm²: 340A (too small)
• $2 \times 240 \text{ mm}^2$ per phase: 680A (too small)
• $2 \times 300 \text{ mm}^2$ per phase: $2 \times 400 \text{ A} = 800 \text{ A}$ per phase ✘
• $3 \times 240 \text{ mm}^2$ per phase: $3 \times 340 \text{ A} = 1020 \text{ A}$ ✘
• $2 \times 400 \text{ mm}^2$ per phase: $2 \times 480 \text{ A} = 960 \text{ A}$ ✘
• $3 \times 185 \text{ mm}^2$ per phase: $3 \times 285 \text{ A} = 855 \text{ A}$ ✘

Solution: Use $2 \times 400 \text{ mm}^2$ per phase (nearest standard size above requirement)

Actual capacity: $2 \times 480 \times 0.94 \times 0.80 = 722$ A > 721.69A ✔

Step 6: Verify voltage drop

For 30m run, using electric tension drop formula:

Where R = 0.0469 Ω/km for 400 mm² copper at 70°C:

Percentage drop: $(1.76 \div 400) \times 100 = 0.44\%$ 0.44% ✔ (well below 3% limit)

Worked Example: Generator Feeder

Scenario: Size feeder for 750 kVA, 480V three-phase generator.

Step 1: Calculate Full Load Current

Step 2: Apply NEC 125% Continuous Load Factor

Per NEC 445.13:

Step 3: Select Conductor Size

From NEC Table 310.16, 75°C copper in conduit:

• 500 kcmil: 430A (too small)
• $2 \times 500 \text{ kcmil}$ per phase: 860A (too small)
• $2 \times 600 \text{ kcmil}$ per phase: $2 \times 490 \text{ A} = 980 \text{ A}$ (marginal)
• $3 \times 500 \text{ kcmil}$ per phase: $3 \times 430 \text{ A} = 1290 \text{ A}$ ✔

Solution: Use $3 \times 500 \text{ kcmil}$ ($253 \text{ mm}^2$) per phase

Step 4: Select Overcurrent Protection

Per NEC 445.13, maximum OCPD = 115% of generator rating:

Select 1000A circuit breaker (next standard size below 1037A)

Step 5: Verify Short Circuit Rating

Generator subtransient reactance X"d = 15%:

Circuit breaker must have interrupting rating $\geq 6014 \text{ A}$. Select 10kA or 14kA rated breaker ✔

Practical Applications

1. Transformer Secondary Cable Sizing

Common transformer sizes and currents at 400V:

2. Switchboard Main Bus Rating

Find busbar amp rating for a building with:

• Transformer: 1600 kVA, 400V
• Demand factor: 80% (NEC 220-87)

Select 2000A busbar (next standard size)

3. Motor Control Center Feeder

Evaluate feeder for MCC serving:

• Connected load: 450 kVA of motors
• Demand factor: 75% (NEC 430-26)
• Energy factor: 0.85 (typical for motors)

With 125% sizing: $486.67 \times 1.25 = 608$ A

Select $3 \times 185 \text{ mm}^2$ cables ($3 \times 285 \times 0.94 \times 0.80 = 643$ A) ✔

Common Mistakes

Mistake 1: Forgetting $\sqrt{3}$ for Three-Phase

Wrong:

Correct:

Impact: Wire would be undersized by 73%, causing overheating and potential fire hazard!

Mistake 2: Using Line-to-Neutral Instead of Line-to-Line

A 100 kVA transformer rated 400V means 400V line-to-line, not line-to-neutral.

Wrong:

Correct:

Mistake 3: Ignoring Safety Factors

Using full load electric current without applying correction factors:

Unsafe: Selecting 150A conductor for 144A load ✘

Safe: $144 \times 1.25 \text{ (continuous) } \div 0.94 \text{ (temp) } \div 0.80 \text{ (grouping) } = 240 \text{ A minimum}$ ✔

Mistake 4: Not Accounting for Harmonic Currents

Modern electronic loads (VFDs, UPS, LED lighting) produce harmonic currents that increase RMS I value and neutral amperage.

Typical derating:

• < 15% THD: No derating
• 15-33% THD: Derate by 0.90
• 33-45% THD: Derate by 0.80
• > 45% THD: Detailed harmonic analysis required

For a data center with 45% THD:

Mistake 5: Confusing Transformer kVA with Load kVA

Scenario: 500 kVA transformer serving 350 kVA load.

Wrong approach: Size cables for 350 kVA load ✘

Correct approach: Size cables for 500 kVA transformer rating ✔

Reason: Cables must handle transformer short-circuit electrical flow and future load growth.

Industry Standards

IEC 60364-5-52 - Cable Selection

Key requirements:

• Conductor sizing based on continuous amp
• Heat level correction factors (Table B.52-14 to B.52-16)
• Grouping factors (Table B.52-17 to B.52-20)
• Volt level drop limits: 3% feeders, 5% total

Installation methods:

• Method A1: Insulated conductors in conduit in thermally insulated wall
• Method C: Single-layer cables on wall or unperforated tray
• Method E: Cables on perforated tray or ladder

NEC (NFPA 70) - Conductor Sizing

Relevant sections:

• 215.2(A)(1): Feeder conductor sizing at 125% continuous load
• 240.4(B): Overcurrent protection for conductors
• 310.15(B): Ampacity tables and correction factors
• 430.24: Machine feeder sizing at 125% of largest drive unit plus sum of others

Derating factors:

• More than 3 conductors: 80% (4-6), 70% (7-9), 50% (10-20)
• Ambient > 30°C: Apply correction per Table 310.15(B)(2)(a)

IEEE 519 - Harmonic Limits

Electric current distortion limits at PCC:

Where:

• $ISC$ = Maximum short-circuit I value at PCC
• $IL$ = Maximum demand load amperage (fundamental) at PCC

Using Our kVA-to-Amp Calculator

Features:

✅ Single-phase and three-phase calculations with automatic formula selection

✅ Line-to-line and line-to-neutral potential options

✅ Instant results with formulas shown

✅ Built-in warnings for high currents (IEC compliance)

✅ Mobile-friendly interface

How to Use:

1. Select phase configuration:

   • Single phase
   • Three-phase (Line-to-Line)
   • Three-phase (Line-to-Neutral)

2. Enter apparent wattage: In kVA (e.g., 500)

3. Enter electrical potential: In volts

   • Single phase: 230V, 120V
   • Three-phase L-L: 400V, 480V, 11000V
   • Three-phase L-N: 230V, 277V

4. Click Measure to get electrical flow in amperes

5. Review warnings if amp exceeds IEEE/IEC thresholds

Our calculations follow industry best practices and have been validated against real-world scenarios.

Conclusion

Converting kVA to amps is fundamental to electrical engineering, essential for cable sizing and selection, overcurrent protection device rating, busbar and switchgear sizing, voltage drop calculations, and thermal analysis of conductors. Understanding the differences between single-phase and three-phase current calculations, applying appropriate safety factors, and considering harmonics for modern electronic loads enables engineers to properly size electrical components and ensure safe, code-compliant installations. Always verify voltage type (line-to-line vs line-to-neutral) on equipment nameplates and account for future expansion when sizing equipment.

Export as PDF — Generate professional reports for documentation, client presentations, or permit submissions.

Key Takeaways

• Convert kVA to amps using formulas: Single-Phase: $I = \frac{\text{kVA} \times 1000}{V}$; Three-Phase: $I = \frac{\text{kVA} \times 1000}{\sqrt{3} \times V_{\text{LL}}}$, where $\sqrt{3} = 1.732$
• Always use $\sqrt{3}$ factor for three-phase line-to-line voltage calculations—omitting it causes 73% underestimation of current, leading to dangerously undersized conductors
• Verify voltage type on equipment nameplates—"400V 3-phase" means 400V line-to-line, not line-to-neutral; using wrong voltage type causes significant calculation errors
• Apply safety factors: 125% for continuous loads (IEC 60364-5-52, NEC 215.2), temperature correction (0.94 at 35°C), grouping factors (0.80 for 4-6 cables), and harmonic derating for electronic loads
• Three-phase systems deliver same power with 33% less current per conductor compared to single-phase, making them more efficient for larger loads and requiring smaller conductors
• For transformers ≥1000 kVA, consider busbar systems instead of cables for better thermal performance and easier maintenance

Further Learning

• Amp to kVA Guide - Reverse conversion from current to apparent power
• Cable Sizing Guide - Comprehensive cable selection guide
• Transformer Sizing Guide - Understanding transformer ratings
• Voltage Drop Guide - Verify voltage drop meets code requirements
• Power Factor Guide - Understanding power factor and correction
• kVA to Amp Calculator - Interactive calculator for conversions

References & Standards

This guide follows established engineering principles and standards. For detailed requirements, always consult the current adopted edition in your jurisdiction.

Primary Standards

IEC 60364-5-52 Low-voltage electrical installations - Part 5-52: Selection and erection of electrical equipment - Wiring systems. Specifies conductor sizing based on current, temperature correction, and grouping factors.

NEC Article 215 Feeders - Requires conductors sized at 125% of continuous load for feeders.

NEC Article 310 Conductors for General Wiring - Provides ampacity tables and correction factors for conductor sizing.

Supporting Standards & Guidelines

IEEE Std 141 Recommended Practice for Electric Power Distribution for Industrial Plants. Provides guidance on load calculations and system design.

IEEE Std 519 Recommended Practice and Requirements for Harmonic Control in Electric Power Systems. Specifies harmonic current limits and derating factors for electronic loads.

IEC 60050 - International Electrotechnical Vocabulary International standards for electrical terminology and definitions.

NEMA Publications National Electrical Manufacturers Association standards for electrical equipment.

Further Reading

• Electrical Installation Guide - Schneider Electric - Comprehensive guide to electrical installation best practices

Note: Standards and codes are regularly updated. Always verify you're using the current adopted edition applicable to your project's location. Consult with local authorities having jurisdiction (AHJ) for specific requirements.

Disclaimer: This guide provides general technical information based on international electrical standards. Always verify calculations with applicable local electrical codes (NEC, IEC, BS 7671, etc.) and consult licensed electrical engineers or electricians for actual installations. Electrical work should only be performed by qualified professionals. Component ratings and specifications may vary by manufacturer.