4-Ton Heat Pump Breaker Size Guide

A 4-ton heat pump (about 48,000 BTU) requires the correct breaker and conductor sizing to protect the unit and comply with the National Electrical Code. This guide explains how to determine the proper breaker size using nameplate data, NEC rules, typical examples, and wiring recommendations so homeowners and technicians can make informed decisions. Always follow the equipment nameplate and local code or consult a licensed electrician.

Parameter	Typical Range	Notes
Cooling Capacity	48,000 BTU (4 Ton)	Standard central residential size
Common Breaker Sizes	40A, 50A, 60A	Depends on motor RLA, MCA, and MOCP
Typical Wire Gauge	8 AWG Copper, 6 AWG Copper	Depends on ampacity and temperature rating

How Breaker Size Is Determined

The correct breaker size for a heat pump is not based solely on tonnage but on the electrical ratings printed on the equipment nameplate, including MCA (Minimum Circuit Ampacity) and MOCP (Maximum Overcurrent Protection). The National Electrical Code (NEC) provides rules for motor and HVAC branch-circuit protection that guide conductor and breaker selection.

Key NEC Rules To Know

NEC Article 440 (Air-Conditioning and Refrigerating Equipment) and Article 430 (Motors and Motor Circuits) apply to heat pumps. Important points are:

• MCA is the minimum ampacity of the branch-circuit conductors; conductors must have ampacity equal to or greater than the MCA.
• MOCP is the maximum breaker or fuse size allowed; the actual breaker can be equal to or less than this value but must still protect conductors and equipment.
• For motor-compressor circuits, NEC often allows overcurrent protection up to the nameplate MOCP because time-delay devices or HACR-rated breakers handle starting currents.
• Conductor sizing generally uses 125% of the motor/compressor running load amps (RLA) when required by the manufacturer nameplate and NEC rules for ampacity calculations.

What The Nameplate Shows And Why It Matters

Heat pump outdoor unit nameplates list values such as RLA (Running Load Amps), LRA (Locked Rotor Amps), MCA, and MOCP. These values are used as follows:

• Use MCA to size the branch-circuit conductors. The conductor ampacity must be at least the MCA.
• Use MOCP to select the maximum allowable breaker or fuse size. The breaker can be equal to or less than MOCP but must be adequate to serve starting currents and not nuisance-trip.
• RLA and LRA help explain why a larger breaker may be necessary because of inrush starting currents for the compressor motor.

Typical Breaker Sizes For A 4-Ton Heat Pump

There is no single breaker size that fits every 4-ton heat pump because electrical demands vary by model and efficiency. However, commonly encountered sizes include:

• 40 Amp Breaker — Used when MCA is around 30–35A and MOCP is 40A; often paired with 8 AWG copper conductors.
• 50 Amp Breaker — Common for units with MCA in the mid-to-high 30s and MOCP of 50A; may still use 8 AWG or step up to 6 AWG depending on conductor ampacity tables.
• 60 Amp Breaker — Required for some high-efficiency or specific compressor types where MOCP is 60A; typically paired with 6 AWG copper conductors.

Examples With Calculations

Example 1: Nameplate Shows RLA 30A, MCA 37A, MOCP 40A. NEC requires conductor ampacity ≥ MCA (37A), so choose conductor rated for 40A or greater. A 40A breaker is permitted since it does not exceed MOCP and matches conductor ampacity. Use 8 AWG copper (depending on insulation temp rating).

Example 2: Nameplate Shows RLA 35A, MCA 44A, MOCP 50A. Conductor ampacity must be ≥44A, so select 6 AWG copper (commonly 55–65A ampacity at 75°C) or verify ampacity per terminations and temperature. A 50A breaker is acceptable because it does not exceed MOCP and provides room for starting current.

Example 3: Nameplate Shows RLA 45A, MCA 56A, MOCP 60A. This unit requires larger conductors (6 AWG copper or possibly 4 AWG depending on temperature rating and conduit conditions). A 60A breaker may be used as long as it does not exceed MOCP.

Wire Gauge Recommendations

Wire gauge depends on the branch-circuit ampacity required by MCA and the terminal temperature rating on the heat pump. Typical conductor recommendations are:

• 8 AWG Copper — Common for 40A–50A circuits depending on temperature listings and installation conditions.
• 6 AWG Copper — Common for 50A–60A circuits; provides margin for 60A breakers and higher MCA values.
• 4 AWG Copper — Occasionally required if MCA approaches 70A or when long runs with voltage drop concerns exist.

Voltage Drop And Long Runs

Voltage drop can affect heat pump performance, especially on long outdoor runs. Aim for less than 3% voltage drop for the branch circuit under full load. If voltage drop exceeds acceptable limits, upsize conductors even if ampacity would allow a smaller gauge. Use conductor size tables or voltage drop calculators to determine necessary gauge for runs over 50 feet.

Breaker Type And Characteristics

Heat pump compressors are motors with high starting currents. The breaker should be sized and rated to tolerate short-duration inrush currents. Features to consider include:

• HACR or Motor-Rated Breakers — Some equipment requires HACR-rated or motor-rated breakers to handle LRA.
• Time-Delay Fuses — Often used in HVAC to prevent nuisance trips during compressor start.
• Manufacturer Requirements — Always follow the unit’s recommended breaker type and any special instructions on the nameplate or installation manual.

Common Mistakes To Avoid

Incorrect breaker selection risks motor damage, nuisance tripping, or code violations. Common mistakes include:

• Sizing the breaker solely by tonnage without checking the nameplate MCA and MOCP.
• Using undersized conductors that meet breaker size but not MCA ampacity.
• Ignoring voltage drop on long runs and not upsizing conductors accordingly.
• Replacing fuses with higher values than MOCP listed on the equipment nameplate.

How To Determine Breaker Size Step-By-Step

1. Locate the unit nameplate and note RLA, MCA, and MOCP.
2. Choose conductor ampacity equal to or greater than MCA per NEC and manufacturer’s instructions.
3. Select a breaker that does not exceed the nameplate MOCP and coordinates with conductor ampacity.
4. Consider voltage drop and increase conductor size if run length or conditions cause excessive drop.
5. Verify breaker type (HACR, time-delay) meets manufacturer and local code requirements.

When To Call A Licensed Electrician

Working with the electrical supply to a heat pump involves safety and code compliance. A licensed electrician should be consulted for:

• Interpreting nameplate values and NEC rules for a specific installation.
• Sizing conductors for long runs, multiple units, or unusual ambient temperatures.
• Installing disconnects, breakers, or new circuits from the service panel.
• Addressing existing issues like nuisance trips, overheating wires, or inadequate service capacity.

Real-World Considerations And Local Code Variations

Local jurisdictions may adopt editions of the NEC with amendments or additional requirements. Additionally, equipment manufacturers sometimes specify conductor sizes or protection that differ from a straightforward NEC calculation. Always prioritize the unit nameplate and local code enforcement over generic guidance.

Safety And Best Practices

Safety should be the primary concern when sizing breakers and conductors for a heat pump. Best practices include following the manufacturer’s installation instructions, using the correct breaker type, installing an outdoor-rated disconnect within sight of the unit, and verifying grounding and bonding are properly completed.

Quick Reference Table For Typical 4-Ton Units

Typical MCA	Typical MOCP	Common Breaker	Suggested Conductor
30–38A	40A	40A	8 AWG Copper (verify temp rating)
39–48A	50A	50A	6 AWG Copper (75°C/90°C rating as applicable)
49–60A	60A	60A	6 AWG Or 4 AWG Copper (check voltage drop)

Final Advice

There is no universal breaker size for a 4-ton heat pump; the correct breaker depends on the unit’s nameplate MCA and MOCP, conductor ampacity, voltage drop, and local code. Always use the nameplate data as the primary source and consult a licensed electrician for installation or upgrades.

For a quick next step, locate the outdoor unit nameplate, note RLA/MCA/MOCP, and bring those numbers to an HVAC technician or electrician for a precise breaker and conductor recommendation.