🔌 AC Unit Size
tons

1 ton = 12,000 BTU/hr cooling capacity

⚡ Electrical Supply
13

Higher rating = more efficient = lower amps

0.9

Typical compressor PF: 0.85–0.95

🛡️ Code & Wiring Settings
ft

Longer runs may need thicker wire

🔄 Include Starting (Inrush) Current
🌡️ Includes Heat Strip / Electric Heat
— A
Live RLA estimate (updates as you type)

Enter your AC details above

Calculating amperage and wire size…

📊 Your Amperage Results
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Minimum Circuit Ampacity (MCA)
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Amps · Includes NEC 125% safety margin
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A
Running Amps (RLA)
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A
Starting Amps (LRA)
🔲
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A
Breaker Size (MOP)
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AWG
Wire Gauge
Load on a Standard 30A Circuit
Light Load Overload —

🔲 Breaker Size Options

Breaker Size
Wire (Copper)
Wire (Aluminum)
Fit
⚠️

Always Verify With a Licensed Electrician

This calculator gives you a strong estimate based on NEC standard formulas. But local codes vary, and your AC unit’s actual nameplate data is the real source of truth. Always check the nameplate on your unit and confirm with a licensed electrician before installing or upgrading any circuit.

📊 Calculation Breakdown

Step
Value
Note
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🛠️ Installation Recommendations

AC Unit Amperage — What You Need to Know

Getting the amperage right matters. Too small a breaker trips constantly. Too small a wire is a fire risk. Here’s how to get it right, in plain language.

⚡

What Is RLA?

RLA stands for Rated Load Amps. It’s how much current your AC compressor draws during normal running operation. You’ll find this on the nameplate sticker on the outdoor unit. It’s the single most important number for sizing your circuit.

🚀

What Is LRA?

LRA stands for Locked Rotor Amps. This is the surge of current when the compressor first starts. It’s much higher than RLA — often 4–6 times higher. This only lasts a fraction of a second but your wiring still needs to handle it safely.

📐

The 125% Rule

The National Electrical Code (NEC) requires your breaker and wire to be sized at 125% of the RLA. This isn’t optional — it’s a safety standard. It accounts for the extra heat generated during continuous running, which AC units do for hours at a time.

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MCA vs MOCP

MCA (Minimum Circuit Ampacity) tells you the smallest wire size allowed. MOCP (Maximum Overcurrent Protection) tells you the largest breaker allowed. Your breaker must be between these two numbers — never below MCA, never above MOCP.

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Why Wire Gauge Matters

Wire that’s too thin for the amperage overheats. This is a genuine fire hazard. Longer wire runs also lose voltage over distance — this is called voltage drop. For runs over 100 feet, you often need to size up one gauge even if the amperage alone wouldn’t require it.

🛡️

Always Check the Nameplate

Calculators like this one give excellent estimates. But the real nameplate data on your specific unit is always the authoritative source. Manufacturing tolerances mean two “3-ton” units from different brands can have slightly different RLA numbers.

📐 The Formulas We Use

RLA (Amps) = Watts ÷ (Volts × Power Factor)  — for single phase MCA = RLA × 1.25  (NEC 125% Rule) MOCP = RLA × 1.25, rounded up to next standard breaker size (max 2.25× RLA)

For three-phase: RLA = Watts ÷ (Volts × 1.732 × Power Factor)
Watts is estimated from tonnage using typical compressor efficiency: roughly 1,200W per ton at SEER 13, adjusted for your SEER/EER rating. This is the standard method used in HVAC load calculations and matches NEC Article 440.

AC Unit Amperage Reference Chart

Typical values for standard residential central AC units at 230V single phase.

AC SizeTypical RLATypical LRAMin BreakerMin Wire (Cu)
1.5 Ton (18,000 BTU)8–9A45–50A15A14 AWG
2 Ton (24,000 BTU)10–12A55–62A20A12 AWG
2.5 Ton (30,000 BTU)12–14A62–70A20A12 AWG
3 Ton (36,000 BTU)14–17A70–85A25A10 AWG
3.5 Ton (42,000 BTU)16–19A80–95A30A10 AWG
4 Ton (48,000 BTU)18–22A90–110A30A10 AWG
5 Ton (60,000 BTU)23–28A110–140A40A8 AWG

Frequently Asked Questions

Most 3-ton residential AC units need a 25–30A double-pole breaker on a 230V circuit. The exact size depends on the unit’s RLA, which is typically 14–17 amps for this size. The breaker should be sized at 125% of RLA, so 14A × 1.25 = 17.5A, rounded up to the next standard breaker size of 20A or 25A. Always check the nameplate MOCP for the exact maximum allowed.
This is the NEC 125% safety rule. AC compressors run continuously for long periods — sometimes hours at a time during hot weather. The code requires extra capacity to handle this continuous duty cycle safely, preventing the wire and breaker from overheating. It also accounts for the brief but very high inrush current (LRA) when the compressor starts.
RLA (Rated Load Amps) is the compressor’s running current at standard test conditions. FLA (Full Load Amps) is often used interchangeably with RLA, especially for fan motors. MCA (Minimum Circuit Ampacity) is RLA plus the 125% safety margin plus any other connected loads, like the fan motor. MCA tells you the smallest wire size that’s legally allowed for this circuit.
No. Wire gauge must always be sized to handle the MCA, regardless of distance. What changes with distance is whether you need to go even thicker than the minimum — this happens on long runs (typically over 100 feet) to prevent voltage drop, which can damage the compressor and reduce its lifespan. Never go below the NEC minimum wire gauge for the amperage.
It might be, but there are other common causes too. A failing compressor, low refrigerant, a seized fan motor, or a loose connection can all cause excess current draw and nuisance trips. Compare your breaker size to the nameplate MOCP first. If the breaker matches the nameplate and still trips, call an HVAC technician — it’s likely a mechanical or electrical fault in the unit itself, not the wiring.
No. This calculator gives you accurate estimates based on standard NEC formulas, which is great for planning, budgeting, and understanding your system. But electrical work involves safety risks and local code requirements that vary by location. Always have a licensed electrician verify the final circuit sizing and perform the actual installation.
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