At a standard US residential voltage of 120V, 30 amps equals exactly 3,600 watts (assuming a direct current or single-phase AC circuit with a power factor of 1.0). If you are working with a 240V single-phase system, 30 amps delivers 7,200 watts. For a 208V 3-phase commercial system, 30 amps yields roughly 10,811 watts. The exact wattage is entirely dependent on the system voltage, the number of phases, and the power factor of the load.
The Core Conversion Formula and Neighboring Values
To convert amperage to wattage, you need to know the voltage. The foundational formula for DC and single-phase AC resistive loads is:
Substituted for 120V: 30A × 120V = 3,600W
This calculation assumes a purely resistive load (like a space heater or incandescent bulb) where the Power Factor (PF) is 1.0. If you are sizing a circuit or evaluating a load, it is highly practical to look at the neighboring current values. A ±20% range around 30 amps gives you a realistic window for fluctuating loads on a 30-amp breaker.
| Current (Amps) | Voltage (120V Nominal) | Calculated Watts (PF=1.0) | Typical Application Context |
|---|---|---|---|
| 24A (-20%) | 120V | 2,880W | NEC maximum continuous load for a 30A breaker |
| 27A (-10%) | 120V | 3,240W | Heavy-duty RV air conditioner startup surge |
| 30A (Base) | 120V | 3,600W | Standard NEMA TT-30 RV receptacle limit |
| 33A (+10%) | 120V | 3,960W | Breaker trip threshold (short-time overload) |
| 36A (+20%) | 120V | 4,320W | Immediate thermal trip zone for standard breakers |
How Voltage, Phase, and Power Factor Shift the Wattage
Presenting a single 120V answer as universal is a critical mistake in electrical design. The wattage delivered by 30 amps shifts dramatically depending on the supply architecture. According to All About Circuits, AC power calculations must account for phase angles in multi-phase systems, introducing the square root of 3 (≈1.732) into the formula for 3-phase power.
The 3-phase formula is: Watts = √3 × Amps × Volts × Power Factor.
Below is a data-dense reference matrix showing exactly how 30 amps translates to watts across standard North American and international voltage configurations. This table assumes a standard power factor of 0.95 for inductive loads and 1.0 for resistive loads.
| System Type | Nominal Voltage | Phase Configuration | Power Factor | Watts at 30A | Common Receptacle / Use Case |
|---|---|---|---|---|---|
| US Residential | 120V | Single-Phase | 1.00 | 3,600W | NEMA TT-30 (RV Parks) |
| US Residential | 240V | Single-Phase (Split) | 1.00 | 7,200W | NEMA 14-30 (Electric Dryers) |
| European / Int'l | 230V | Single-Phase | 0.95 | 6,555W | IEC 60309 32A Caravan Plugs |
| US Commercial | 208V | 3-Phase (Wye) | 0.90 | 9,826W | HVAC Compressors, Shop Tools |
| US Commercial | 480V | 3-Phase (Delta) | 0.85 | 21,238W | Industrial Motor Control Centers |
When the Conversion is Meaningless and NEC Derating Rules
There are two primary scenarios where simply multiplying 30 amps by a voltage figure will give you dangerous or useless data: unknown power factors on inductive loads, and ignoring National Electrical Code (NEC) continuous load derating.
The Power Factor Trap
If you are measuring 30 amps on a clamp meter feeding a large induction motor, an arc welder, or a bank of uncorrected fluorescent ballasts, the conversion to "real power" (watts) is meaningless unless you know the Power Factor (PF). A motor drawing 30A at 240V with a poor PF of 0.65 is only doing 4,680 watts of actual mechanical work, despite pulling 7,200 volt-amps (VA) of apparent power from the grid. Sizing a generator or solar inverter based purely on the 7,200W resistive calculation will result in severe voltage sag and equipment failure. Always use a true-RMS power meter to measure PF on inductive loads before sizing upstream equipment.
NEC 80% Continuous Load Rule
From a practical wiring standpoint, a 30-amp breaker does not safely support 3,600 watts of continuous draw. The NFPA 70 (NEC) Article 210.20 mandates that if a load is expected to run for three hours or more (like an EV charger, a server rack, or a kiln), the circuit must be derated to 80% of the breaker's rating.
Quick Reference FAQ
How many watts can a 30-amp RV hookup handle?
A standard 30-amp RV hookup (NEMA TT-30R) provides 120V single-phase power. The absolute maximum is 3,600 watts. However, because RV air conditioners and microwaves often run simultaneously for hours, you should plan your load management around a continuous limit of 2,880 watts to prevent tripping the pedestal breaker.
Can I run a 7,000-watt electric heater on a 30-amp 240V breaker?
No. While 30A × 240V = 7,200W mathematically, a 7,000W heater is a continuous load. Applying the NEC 80% rule, a 30A 240V circuit can only handle 5,760W continuously. You must upgrade to a 40-amp breaker (with 8 AWG copper wire) to safely run a 7,000W heater.
What size solar inverter do I need for a 30-amp 120V workshop circuit?
If your workshop tools draw up to 30A at 120V (3,600W peak), you need an inverter rated for at least 4,000W to 5,000W to handle the startup surge currents (locked rotor amps) of tools like table saws and air compressors, which briefly pull 2 to 3 times their running wattage.
Does wire gauge change the wattage calculation?
Wire gauge (like 10 AWG vs 8 AWG) does not change the fundamental math of $W = A \times V$. However, undersized wire causes voltage drop over distance. If you run 10 AWG wire 150 feet to a 30A load, the voltage at the receptacle might drop from 120V to 114V. Your actual delivered wattage drops to 3,420W, and the tool will draw higher amps to compensate, generating excess heat.
