AC Circuit Breaker Size Calculator

Determine the correct circuit breaker size for your air conditioner by entering the unit specifications below.

Check your AC's nameplate for Minimum Circuit Ampacity (MCA)
Found on AC nameplate as RLA or FLA (Full Load Amps)
Measure the wire path from AC to electrical panel

Understanding AC Circuit Breaker Sizing

Proper circuit breaker sizing is crucial for the safe operation of your air conditioning system. The breaker protects both your AC unit and home's electrical system from overload and short circuits. Understanding the factors involved helps ensure a safe and compliant installation.

Key Terms and Concepts

Minimum Circuit Ampacity (MCA)

The minimum circuit ampacity represents the minimum wire size and circuit breaker rating required for safe operation. This value is typically marked on the AC unit's nameplate.

Maximum Overcurrent Protection (MOCP)

The maximum size of the circuit breaker or fuse that can be used to protect the AC unit. This value should never be exceeded, even if larger wire sizes are used.

Running Load Amps (RLA)

The current draw of the unit during normal operation. Also known as Full Load Amps (FLA), this is typically lower than the MCA.

Locked Rotor Amps (LRA)

The maximum current draw when the compressor starts. This momentary surge must be considered when sizing the circuit breaker.

Standard Circuit Breaker Sizes for AC Units

AC Type Typical BTU Range Voltage Common Breaker Sizes
Window AC 5,000-12,000 115V 15-20A
Mini-Split 9,000-24,000 220-240V 15-30A
Central AC 24,000-60,000 220-240V 30-60A
Commercial AC 60,000+ 208-240V 60-100A
*Always verify specific requirements with your unit's nameplate and local electrical codes.

Wire Sizing Requirements

Circuit Breaker Size Minimum Wire Gauge (Copper) Maximum Run Length* Wire Type
15A 14 AWG 50 ft THHN/THWN-2
20A 12 AWG 70 ft THHN/THWN-2
30A 10 AWG 110 ft THHN/THWN-2
40A 8 AWG 170 ft THHN/THWN-2
50A 6 AWG 270 ft THHN/THWN-2
60A 4 AWG 430 ft THHN/THWN-2
*Maximum run lengths based on 3% voltage drop at 240V. Adjust for different voltages and conditions.

Factors Affecting Circuit Breaker Selection

Unit Specifications

  • Nameplate MCA and MOCP values
  • Operating voltage requirements
  • Single or three-phase power
  • Starting current requirements

Installation Factors

  • Distance from electrical panel
  • Ambient temperature
  • Conduit fill requirements
  • Voltage drop considerations

Code Requirements

  • National Electrical Code (NEC)
  • Local building codes
  • HVAC manufacturer specifications
  • Utility company requirements

Safety Considerations

  • Overload protection
  • Short circuit protection
  • Ground fault protection
  • Arc fault requirements

Installation Requirements

Disconnect Requirements

  • Visible disconnect within sight of unit
  • Maximum distance of 50 feet from unit
  • Readily accessible location
  • Proper weatherproof enclosure for outdoor units
  • Appropriate ampacity rating

Grounding Requirements

  • Equipment grounding conductor sized per NEC
  • Proper bonding at disconnect
  • Ground rod requirements for outdoor units
  • Connection to building grounding system

Common Installation Mistakes

Undersized Circuit Breakers

Using a breaker that's too small can cause nuisance tripping and prevent proper AC operation. Signs include:

  • Frequent breaker trips on hot days
  • Tripping during startup
  • Inability to reach desired temperature

Oversized Circuit Breakers

Using too large a breaker compromises safety protection. Problems include:

  • Inadequate short circuit protection
  • Potential fire hazards
  • Code compliance issues

Incorrect Wire Sizing

Wire size must match both breaker and distance requirements:

  • Voltage drop over long runs
  • Temperature derating factors
  • Conduit fill calculations

Frequently Asked Questions About AC Circuit Breakers

General Circuit Breaker Questions

Why does my AC need a dedicated circuit?

Air conditioners require dedicated circuits for several reasons:

  • High power draw during operation
  • Significant startup current requirements
  • Consistent power availability
  • Code compliance requirements
  • Prevention of circuit overload

Can I use a larger circuit breaker than specified?

No, exceeding the maximum overcurrent protection (MOCP) rating is unsafe and violates code:

  • May not provide proper short circuit protection
  • Could allow dangerous current levels
  • Voids equipment warranty
  • Violates electrical codes

Installation and Safety Questions

Do I need a licensed electrician to install an AC circuit?

Yes, professional installation is typically required because:

  • Local codes usually require licensed installers
  • Proper permits must be obtained
  • Safety inspections are necessary
  • Warranty may require professional installation
  • Complex calculations and code knowledge needed

What causes an AC circuit breaker to trip?

Common causes include:

  • Compressor short circuit
  • Excessive current draw
  • Loose electrical connections
  • Dirty air filters restricting airflow
  • Low refrigerant causing overwork
  • Damaged or aging wiring

Technical Questions

How do I calculate voltage drop?

Voltage drop calculation factors:

  • Circuit current (amps)
  • Wire length (one-way distance)
  • Wire resistance per foot
  • System voltage
  • Maximum allowed drop (usually 3%)

What's the difference between HACR and standard breakers?

HACR (Heating, Air Conditioning, Refrigeration) breakers:

  • Specifically rated for AC/heating equipment
  • Designed for high inrush currents
  • Required by many manufacturers
  • May have special trip characteristics