What Is the Resistance and Power for 240V and 120A?

240 volts and 120 amps gives 2 ohms resistance and 28,800 watts power. Ohm's Law (V = IR) and the power equation (P = VI) connect all four electrical values. Knowing any two lets you calculate the other two instantly.

240V and 120A

2 Ω | 28,800 W

Voltage (V)240 V

Current (I)120 A

Resistance (R)2 Ω

Power (P)28,800 W

Volts

Amps

Ohms

Watts

28,800

Formulas & Step-by-Step

Resistance

R = V ÷ I

240 ÷ 120 = 2 Ω

Power

P = V × I

240 × 120 = 28,800 W

Verification (alternative formulas)

P = I² × R

120² × 2 = 14,400 × 2 = 28,800 W ✓

P = V² ÷ R

240² ÷ 2 = 57,600 ÷ 2 = 28,800 W ✓

Circuit Analysis

Heat Dissipation

This circuit dissipates 28,800 watts of power as heat. In a resistor, all electrical energy at steady state converts to thermal energy. The actual component power rating needs headroom above this steady-state figure, but the specific derating depends on resistor type (carbon-comp, metal-film, wirewound each behave differently), ambient temperature, airflow or heat-sinking, and whether the load is continuous or pulsed. Check the resistor datasheet for the manufacturer-specific derating curve rather than applying a blanket margin.

If You Change the Resistance

Resistance	Current	Power	Change
1 Ω	240 A	57,600 W	Lower R = more current
1.5 Ω	160 A	38,400 W	Lower R = more current
2 Ω	120 A	28,800 W	Current
3 Ω	80 A	19,200 W	Higher R = less current
4 Ω	60 A	14,400 W	Higher R = less current

Same Resistance at Different Voltages

Holding the resistance constant at 2Ω, here is how current and power scale with source voltage. This is a reference table, not a set of separate circuit scenarios: each row is the same resistor under a different applied voltage.

Voltage	Current (at 2Ω)	Power
5V	2.5 A	12.5 W
12V	6 A	72 W
24V	12 A	288 W
48V	24 A	1,152 W
120V	60 A	7,200 W
208V	104 A	21,632 W
230V	115 A	26,450 W
240V	120 A	28,800 W
480V	240 A	115,200 W

Related Calculations

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Frequently Asked Questions

What is the resistance for 240V and 120A?expand_more

R = V ÷ I = 240 ÷ 120 = 2 ohms.

What determines wire size for 120A?expand_more

Wire sizing for a given current is not an Ohm's Law calculation. It depends on run length, source voltage, voltage-drop target, conductor material, insulation and termination temperature rating, cable type, and ambient and bundling conditions. The dedicated wire-size calculator takes those variables as input.

How are voltage, current, resistance, and power related?expand_more

Ohm's Law (V = IR) and the power equation (P = VI) connect all four. Given any two, you can calculate the other two.

How much heat does 2 ohms produce at 240V?expand_more

All 28,800W is dissipated as heat in a pure resistor at steady state. The component power rating needs headroom above this steady-state figure, but the specific derating depends on resistor type (carbon-comp, metal-film, wirewound each behave differently), ambient temperature, airflow or heat-sinking, and whether the load is continuous or pulsed. Check the resistor datasheet for the manufacturer-specific derating curve.

Does Ohm's Law work for AC circuits?expand_more

For purely resistive loads, yes. For reactive loads, use impedance (Z) instead of resistance (R). Z includes both resistance and reactance, and the V/I phase shift shows up in power factor.

This calculator provides estimates for reference purposes only. Always consult a licensed electrician and verify compliance with the National Electrical Code (NEC) and local electrical codes before performing any electrical work.