3 Ton Heat Pump Breaker Size Guide

The right breaker size for a 3 ton heat pump depends on the unit’s rated compressor and fan current, the manufacturer’s specifications, and National Electrical Code (NEC) requirements. This guide explains how to determine proper breaker and wire sizes, typical rule-of-thumb values, and important considerations for safe, code-compliant installation.

Heat Pump Type	Typical Breaker Size	Typical Wire Gauge	Notes
Air-Source 3 Ton (13–16 SEER)	30–40 A	10–8 AWG	Depends on compressor LRA/FLA and PSC vs. RLA motors
3 Ton Mini-Split	25–40 A	10–8 AWG	Outdoor unit condensing unit often smallest; check nameplate
Heat Pump With High LRA	40–50 A	8–6 AWG	Large starting current may require larger breaker and contactor

How Breaker Size Is Determined

Breaker sizing is based on the unit’s full-load current (FLC/FLA) published on the equipment nameplate and NEC rules for maximum continuous and non-continuous loads. The installer must review the manufacturer’s nameplate values, which include compressor motor FLA and minimum circuit ampacity (MCA) and maximum fuse or circuit breaker size (Max OCP).

Key electrical values to find on the nameplate: FLA (Full Load Amps), LRA (Locked Rotor Amps), MCA (Minimum Circuit Ampacity), and Max OCP (Maximum Overcurrent Protection).

NEC Rules Relevant To Heat Pump Breaker Sizing

The NEC provides guidelines that impact breaker selection for HVAC equipment. Two particularly important rules are: NEC 210.19(A)(1) for branch-circuit conductors and NEC 440 for air-conditioning and refrigeration equipment.

NEC 440.22(B) requires branch-circuit overcurrent protection not to exceed the equipment’s listed maximum. NEC 440.4 requires the use of the manufacturer’s nameplate data for sizing conductors and overcurrent protection.

Typical 3 Ton Heat Pump Electrical Specs

Most residential 3 ton heat pumps range from 36,000 Btu/h nominal capacity. Typical electrical characteristics vary with compressor type, SEER rating, and whether the indoor unit contains a blower motor on a separate circuit.

• Typical Full Load Amps (FLA): 15–30 amps for the compressor/condenser only, depending on efficiency and design.
• Typical Locked Rotor Amps (LRA): 80–200 amps for single-stage scroll or reciprocating compressors.
• Typical MCA: 20–35 amps; this is the minimum conductor ampacity required by the manufacturer.

Common Breaker Sizes For 3 Ton Units

While the exact size must come from the nameplate, installers commonly use the following as starting points.

• 30 Amp Breaker: Used for some high-efficiency 3 ton units with low FLA and MCA ratings near 20–22 amps and Max OCP 30 A.
• 35 Amp Breaker: Frequently used where MCA is 25–28 amps and Max OCP allows 35 A.
• 40 Amp Breaker: Common for many 3 ton heat pumps with higher FLA or conservative MCA values; often paired with 8 AWG copper conductors.

Minimum Circuit Ampacity (MCA) vs Maximum Overcurrent Protection (Max OCP)

MCA is the minimum conductor ampacity required to handle continuous load without overheating. Max OCP is the largest overcurrent protective device allowed by the manufacturer. These two values together determine conductor size and breaker selection.

Example: If a nameplate shows MCA 25 A and Max OCP 40 A, the installer must use a conductor rated at least 25 A continuous (usually 8 AWG copper for 40°C terminals) and may protect the circuit with a breaker up to 40 A per the Max OCP value.

Conductor Sizing Guidelines

Conductor sizing is influenced by MCA and terminal temperature ratings. Typical copper wire choices for residential 3 ton heat pumps:

• 10 AWG copper: Common for circuits up to about 30 A protected; used when MCA ≤ 30 A and terminal ratings allow.
• 8 AWG copper: Common when MCA is 30–40 A or when parent feeder requires larger ampacity.
• 6 AWG copper: Used when MCA exceeds ~40 A or when long runs cause voltage drop concerns.

Voltage drop consideration: Keep voltage drop under 3% for the branch circuit to maintain performance; for long runs, increase conductor size accordingly.

Examples And Calculations

Example 1: Nameplate MCA 22 A, Max OCP 30 A

Based on the nameplate, minimum wire must be rated ≥22 A. Common practice uses 10 AWG copper (rated 30 A in typical installations) with a 30 A breaker, which complies with Max OCP and provides adequate conductor ampacity.

Example 2: Nameplate MCA 30 A, Max OCP 40 A

Conductor should be rated ≥30 A; installers commonly use 8 AWG copper (rated 40–55 A depending on conditions) with a 40 A breaker. This meets MCA and does not exceed Max OCP.

Example 3: High Starting Current Compressor

If the unit lists high LRA or a high MCA (35–40 A) and a Max OCP of 50 A, the typical choice might be 6 or 8 AWG conductors with a 45–50 A breaker, per the manufacturer’s guidance and local code enforcement.

Differences Between Fuse And Circuit Breaker Ratings

Manufacturers sometimes specify fuses instead of circuit breakers for Max OCP. A fuse rating may differ due to time-delay characteristics. When a Max OCP is given in fuse amperes, a similarly rated circuit breaker may or may not be allowed; refer to the equipment literature and NEC 440.22.

Rule of thumb: Use the manufacturer’s listed Max OCP and use the same rating for breakers unless the equipment manual specifies fuse-only protection.

Starting Current (LRA) And Impact On Protection

Locked Rotor Amps (LRA) represent the compressor’s starting current and can be many times the FLA. Breakers are designed to tolerate short surges; therefore, a breaker sized per Max OCP is acceptable even though LRA is much higher.

Important: Do not size the breaker to LRA. Instead, rely on MCA and Max OCP values on the nameplate and NEC guidance.

Split Systems, Mini-Splits, And Multi-Zone Units

Mini-split heat pump outdoor units and multi-zone systems may have different electrical requirements from traditional packaged or split systems. Some multi-zone systems require larger breakers due to multiple indoor heads and higher aggregate loads.

Always check the outdoor unit nameplate for MCA and Max OCP. For systems with separate indoor fan-coil electrical feeds, size those circuits per manufacturer specs for blower motors and controls.

Safety, Code Compliance, And Permits

Local codes may have amendments to the NEC. Many jurisdictions require permits and inspections for HVAC electrical work. Improper breaker or conductor sizing can cause nuisance trips or create fire hazards.

Always: Obtain local permits where required, follow manufacturer installation instructions, and have installations inspected by qualified personnel.

When To Consult A Licensed Electrician Or HVAC Technician

If the nameplate is missing, unclear, or if the installation involves long runs, multiple units on a single service, or complex control wiring, consult a licensed electrician or HVAC technician.

Professional assessment is essential when ampacity increases, or when adding subpanels, service upgrades, or smart load management devices.

Common Mistakes To Avoid

• Using a breaker sized to LRA rather than following MCA/Max OCP guidance.
• Ignoring voltage drop for long runs, which can reduce compressor life.
• Using undersized conductors or unsecured wire terminations that overheat under continuous load.
• Equating compressor nameplate FLA with MCA—always use the provided MCA value for conductor sizing.

Quick Reference Table For Typical 3 Ton Units

Condition	Typical MCA	Typical Max OCP	Common Breaker	Common Wire
High-Efficiency 3 Ton	20–25 A	30 A	30 A	10 AWG Cu
Standard 3 Ton	25–30 A	35–40 A	35–40 A	8–10 AWG Cu
High MCA/Heavy Start	30–40 A	45–50 A	45–50 A	6–8 AWG Cu

Practical Checklist For Sizing Breaker And Wire

1. Locate the outdoor unit nameplate and record MCA and Max OCP.
2. Confirm supply voltage (208/230 V single-phase or three-phase) and system type.
3. Select conductor gauge to meet or exceed MCA and to limit voltage drop to <3% if possible.
4. Choose a breaker rating that does not exceed the Max OCP and matches local code allowances.
5. Consider motor starting characteristics and coordinate with contactor and motor protection where required.
6. Obtain permits and schedule inspections if local regulations require them.

Key Takeaways

The breaker size for a 3 ton heat pump is not one-size-fits-all. It typically ranges from 30 to 50 amps depending on MCA, Max OCP, and unit design. Always use the manufacturer’s nameplate values and NEC rules when determining breaker and wire sizes. When in doubt, consult a licensed electrician or HVAC technician to ensure safe, compliant installation.

For precise breaker sizing, refer to the specific equipment nameplate, the manufacturer’s installation manual, and local electrical codes. Proper sizing maximizes performance, reduces nuisance trips, and prevents electrical hazards.