VA to Amp Calculator - Convert Apparent Power to Current

Introduction

UPS systems, small transformers, and power supplies are rated in VA—but circuit breakers, conductors, and fuses must be sized in amperes. This VA-to-amp conversion is the essential translation from equipment capacity to infrastructure requirements.

Why This Conversion Matters

When specifying a 2,000 VA UPS, the installation question is immediate: what circuit breaker protects it, and what wire gauge feeds it? At 230V single-phase, that UPS draws 8.7A—requiring at minimum a 10A circuit with appropriate conductors. Every equipment selection flows through this conversion: the VA rating determines circuit protection, conductor sizing, and panel loading. Get it wrong, and circuits trip under normal operation or conductors overheat from sustained current they weren't designed to carry.

The Fundamental Challenge

Unlike kW-to-amp conversions, VA-to-amp conversion doesn't require power factor—VA already represents total current including both real and reactive components. This makes the calculation simpler but requires careful attention to voltage type: three-phase systems use the $\sqrt{3}$ factor with line-to-line voltage. A 50 kVA transformer at 400V draws 72A per line, not 125A (which you'd get by ignoring the $\sqrt{3}$ factor). This guide systematically addresses single-phase and three-phase configurations.

What You'll Learn

This guide provides the complete methodology for VA-to-amp conversions across all system configurations. You'll master the formulas for single-phase and three-phase systems per IEEE 1459-2010 definitions. Practical examples demonstrate transformer full-load current calculations, UPS circuit sizing, and conductor selection with safety factors. Reference tables provide quick-reference multipliers for common voltage levels and standard equipment current ratings.

Quick Answer: How to Convert VA to Amps

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

Conversion Formulas

Where:

• $I$ = Current (A)
• $S$ = Apparent power (VA)
• $V$ = Voltage (V)
• $\sqrt{3}$ = 1.732

Note: For kVA, multiply by 1000 first: $S(\text{VA}) = \text{kVA} \times 1000$

Worked Examples

Reference Table

Key Standards

Understanding Apparent Power and Current

Apparent Power (VA)

Apparent energy is the product of RMS electrical potential and RMS amperage, measured in volt-amperes (VA). Understanding the difference between apparent electrical power (VA) and real wattage (watts) is fundamental for proper equipment sizing.

Key Points:

• Measured in VA or kVA
• Includes reactive capacity
• Used for equipment rating
• Always $\geq$ real energy (W)
• For electrical power factor relationships, see our wattage factor guide

Current (A)

Electrical flow is the flow of electric charge, measured in amperes (A). For conductor sizing based on calculated amp, refer to our conductor sizing guide.

Key Points:

• Measured in amperes (A)
• Determines conductor size
• Affects protection sizing
• Causes heat in conductors ($I^2R$ losses)

Voltage (V)

V value is the electrical potential difference. The relationship between electric tension, electric current, and resistance is explained by Ohm's Law.

Key Points:

• Standard values: 120V, 230V, 400V
• Affects I value magnitude
• Determines installation volt level class
• Influences equipment selection
• See our potential drop guide for wiring run considerations

The Formulas

DC and AC Single-Phase Current Formula

For DC and AC single-phase systems:

Where:

• $I(A)$ = Amperage in amperes
• $S(VA)$ = Apparent capacity in volt-amperes
• $V(V)$ = V value in volts

AC Three-Phase Current Formula (Line-to-Line)

For three-phase systems with line-to-line electric tension:

Where:

• $V_{\text{L-L}}$ = Line-to-line volt level
• $\sqrt{3} \approx 1.732$ (three-phase factor)

AC Three-Phase Current Formula (Line-to-Neutral)

For three-phase systems with line-to-neutral potential:

Where:

• $V_{\text{L-N}}$ = Line-to-neutral electrical potential

Step-by-Step Calculations

Example 1: Single-Phase Current from VA

Problem: A UPS rated at 2000 VA operates at 230 V. Compute the output electrical flow.

Solution:

1. Identify equipment type: AC Single-Phase

2. Given values:

   • Apparent Energy (S) = 2000 VA
   • V value (V) = 230 V

3. Apply single-phase formula:

4. Result: The output amp is approximately 8.7 A.

Example 2: Three-Phase Current from kVA

Problem: A 50 kVA transformer has 400 V line-to-line electric tension. Find the rated electric current.

Solution:

1. Identify infrastructure type: AC Three-Phase

2. Given values:

   • Apparent Electrical power (S) = 50 kVA = 50,000 VA
   • Volt level ($V_{\text{LL}}$) = 400 V

3. Apply three-phase formula:

4. Result: The rated I value is approximately 72.2 A.

Example 3: DC Current from VA

Problem: A DC wattage supply rated at 1200 VA outputs 48 V. Evaluate the amperage.

Solution:

1. Identify setup type: DC

2. Given values:

   • Apparent Load (S) = 1200 VA
   • Potential (V) = 48 V

3. Apply DC formula:

4. Result: The output electrical flow is 25 A.

Practical Examples

Example 4: UPS Current Calculation

Scenario: A 3 kVA UPS operates at 230 V single-phase. What is the maximum output amp?

Given:

• Apparent Capacity = 3 kVA = 3000 VA
• Electrical potential = 230 V

Analysis:

Result: The maximum output electric current is approximately 13 A.

Application: This UPS can supply loads drawing up to 13 A at 230 V. For UPS sizing with energy factor considerations, see VA to kW conversion and kVA to kW guide.

Example 5: Transformer Secondary Current

Scenario: A 100 kVA distribution transformer has 400 V three-phase secondary. Measure the full-load secondary I value.

Given:

• Apparent Electrical power = 100 kVA = 100,000 VA
• V value (LL) = 400 V

Determination:

Result: The full-load secondary amperage is approximately 144 A.

Protection: Use circuit breakers rated for at least 160 A (next standard size). For transformer protection coordination and fault electrical flow analysis, refer to our short circuit evaluation guide.

Conductor Sizing: Apply 125% safety factor for continuous loads: $144 \times 1.25 = 180$ A minimum conductor capacity. Use our lead sizing guide for detailed ampacity calculations.

Example 6: Generator Current Rating

Scenario: A portable generator rated at 5500 VA provides 230 V single-phase output. Assess the amp capacity.

Given:

• Apparent Wattage = 5500 VA
• Electric tension = 230 V

Assessment:

Result: The generator can supply approximately 24 A.

Usage: This is suitable for loads totaling less than 24 A at 230 V.

System Types

DC Systems

Characteristics:

• Constant volt level and electric current
• Apparent load = Real capacity
• No reactive component
• Simple solution using Ohm's Law principles

Formula: $I(A) = \frac{S(VA)}{V(V)}$

Applications:

• DC energy supplies and battery life calculations
• Battery chargers
• Telecommunications equipment
• Solar inverter DC side and solar collector integration

AC Single-Phase Systems

Characteristics:

• Alternating I value
• Apparent electrical power $\geq$ Real wattage
• Common in residential
• 230 V or 120 V standard

Formula: $I(A) = \frac{S(VA)}{V(V)}$

Applications:

• Residential UPS systems
• Small transformers
• Single-phase generators
• Home electrical service

AC Three-Phase Systems

Characteristics:

• Three alternating currents ($120°$ phase separation)
• More efficient for large loads - see kVA to amp calculations
• Industrial applications
• 380 V, 400 V, or 480 V standard voltages

Formula: $I(A) = \frac{S(VA)}{\sqrt{3} \times V_{\text{L-L}}(V)}$

Applications:

• Industrial transformers and transformer sizing
• Large UPS systems
• Commercial generators and horsepower conversions
• Distribution systems including cooling loads and HVAC equipment

Equipment Current Ratings

Transformer Full-Load Currents

UPS Current Ratings

Conductor Sizing

Current Carrying Capacity

After calculating amp from VA, select conductors based on comprehensive sizing criteria. Use our detailed conductor sizing guide for complete ampacity calculations.

Factors to Consider:

1. Continuous load: Electric current $\times 1.25$ (see short circuit protection)
2. Ambient temperature: Apply derating factors per IEC standards
3. Installation method: Conduit, wiring tray, direct burial
4. Number of conductors: Apply grouping factor
5. V value drop: Check acceptable limits using our electric tension drop calculator

Example Conductor Sizes (Copper, 75°C):

Standards and References

International Standards

• IEEE Std 1459-2010: Definitions for measurement of electric load quantities
• IEC 60076: Capacity transformers
• IEC 62040-3: UPS systems - Method of specifying performance
• IEC 60364-5-52: Electrical installations - Selection of equipment

Transformer Standards

• IEC 60076-1: General requirements
• IEC 60076-2: Temperature rise
• IEEE C57.12.00: General requirements for transformers

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

Conclusion

Converting apparent power (VA) to current (amps) is essential for:

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• Transformer load verification
• UPS sizing
• Generator capacity checking
• Circuit design and protection sizing

Key formulas:

• Single-phase: $I = \frac{S(\text{VA})}{V}$
• Three-phase: $I = \frac{S(\text{VA})}{\sqrt{3} \times V}$

Important points:

• VA to amp conversion does NOT require power factor (unlike kW to amp)
• Always apply 125% safety factor for continuous loads
• Verify calculations against equipment specifications and electrical codes

Key Takeaways

Formulas:

• Single-phase: $I = \frac{S(\text{VA})}{V}$
• Three-phase: $I = \frac{S(\text{VA})}{\sqrt{3} \times V}$

Important rules:

• No power factor needed (VA already includes total current)
• Convert kVA to VA first: multiply by 1000
• Apply 125% safety factor for continuous loads (>3 hours)
• Use line-to-line voltage for three-phase systems
• Verify against equipment nameplate ratings

Further Learning

• Amp to VA Guide - Reverse conversion from current to apparent power
• kVA to Amp Guide - Direct kVA ratings to current
• Transformer Sizing Guide - Sizing transformers based on kVA requirements
• Cable Sizing Guide - Selecting conductors based on calculated current
• VA to Amp Calculator - Interactive calculator for current conversion

Calculator

Use our interactive calculator to convert volt-amperes to amperes:

Transformer Sizing Comparison

Understanding how transformer VA rating affects I value capacity at different voltages:

Key Insights:

• Volt level ratio impact: 11kV primary draws 28× less amp than 400V secondary for same capacity
• Conductor economics: Higher potential = dramatically smaller primary conductors
• Protection sizing: Apply 125-150% of full-load electric current for continuous rating
• Overload capacity: Most transformers rated for 110-125% continuous, 150% for 30 minutes emergency
• For transformer short-circuit withstand calculations, see our short circuit guide

UPS Configuration Comparison

How UPS topology affects I value ratings for same VA capacity (10 kVA example):

Selection Criteria:

• Online topology: Best for sensitive equipment, continuous conditioning
• Line-interactive: Good balance of protection and effectiveness
• Offline: Most economical, adequate for non-critical loads
• Input amp: Higher for online due to battery charging + conversion losses
• For related energy quality topics, see electrical phase angle correction and volt to watt conversion

Equipment Sizing Process

Follow these steps to size equipment and conductors from VA ratings:

Step 1: Identify Apparent Load (VA)

• Check nameplate or datasheet for VA or kVA rating
• Convert kVA to VA: multiply by 1000

Step 2: Calculate Current

• Single-phase: $I = \frac{S(\text{VA})}{V}$
• Three-phase: $I = \frac{S(\text{VA})}{\sqrt{3} \times V}$ where $\sqrt{3} = 1.732$

Step 3: Apply Safety Factors

• Continuous load: $I \times 1.25$
• Transformer: $I \times 1.25$ to $1.5$
• UPS: $I \times 1.2$ (account for losses)

Step 4: Select Components

• Conductor: Use ampacity tables (NEC Table 310.16 or IEC 60364-5-52)
• Breaker: Next standard size up
• Equipment: Match voltage rating

Step 5: Verify Requirements

• ✔ Voltage drop acceptable (<3-5%)
• ✔ Short-circuit rating adequate
• ✔ Temperature derating applied
• ✔ NEC/IEC code compliance

Practical Example:

50 kVA transformer, 400V 3-phase

1. Apparent Capacity: 50 kVA = 50,000 VA
2. Three-phase → $I = \frac{50,000}{1.732 \times 400} = 72.2$ A
3. Apply 125% factor → $72.2 \times 1.25 = 90.3$ A required
4. Select: 95A conductor (50 mm² copper), 100A breaker
5. Verify: VD acceptable ✔ , SC rating adequate ✔

For complete conductor selection methodology, use our wire sizing calculator.

Power System Comparison

Critical Distinctions:

• VA (Apparent Wattage): Total load delivered by source (includes reactive component)
• Watts (Real Capacity): Actual energy consumed and converted to work
• VAR (Reactive Electrical power): Wattage oscillating between source and load
• Load Factor: Ratio of real to apparent capacity (W/VA)

Sizing Rule: Always use VA for conductor and transformer sizing, not watts alone.

How Do You Troubleshoot?

Common issues and solutions:

Common Mistakes

Advanced Design Considerations

For professional installations, also consider:

Code compliance:

• Conductor ampacity per NEC Table 310.15(B)(16)
• OCPD sized at 125% minimum for continuous loads
• Equipment rated for available fault current
• Proper grounding and bonding per NEC Article 250

References & Standards

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

Primary Standards

IEEE 1459-2010 Standard definitions for the measurement of electric power quantities under sinusoidal, nonsinusoidal, balanced, or unbalanced conditions. Defines apparent power (VA) and specifies that VA represents total current draw, requiring no power factor for current calculation (unlike kW to amp conversion).

IEC 60076 Power transformers. Specifies transformer kVA ratings and full-load current calculations. Transformer current: I = (kVA × 1000) / (√3 × V) for three-phase systems. Defines transformer sizing based on apparent power (kVA), not real power (kW).

Supporting Standards & Guidelines

NEC Article 210.19 Branch circuits. Specifies 125% safety factor for continuous loads (>3 hours operation) when sizing conductors and overcurrent protection devices.

IEC 60050 - International Electrotechnical Vocabulary International standards for electrical terminology and definitions, including apparent power and current terms.

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.