Apparent vs true power: what it means for the Texas exam

Bonding Jumper editorial teamSources checked 26 Oct 20263 min read

True power, measured in watts, is the power a load actually turns into heat, light or motion. Apparent power, measured in volt-amperes, is simply the voltage times the current, the total the conductors and transformers must carry. They are equal only when current and voltage are in step. When they are not, the difference is reactive power, measured in VAR.

A right triangle with the base labeled true power in kW, the vertical side labeled reactive power in kVAR and the long slope labeled apparent power in kVA, with example values 8, 6 and 10 and the angle theta at the base corner — The power triangle: watts along the bottom, VAR up the side, volt-amperes on the slope.

The power triangle

The three quantities form a right triangle. True power is the base, reactive power is the upright side and apparent power is the slope:

Apparent power squared = true power squared + reactive power squared
True power = apparent power × power factor

A worked example with invented numbers: a load uses 8 kW of true power and 6 kVAR of reactive power. Apparent power is the square root of 64 + 36, which is the square root of 100, or 10 kVA. The power factor is 8 ÷ 10 = 0.8.

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The formulas

Single-phase apparent power: VA = volts × amperes.
Three-phase apparent power: VA = 1.732 × line volts × line amperes.
True power: multiply either of those by the power factor.

On a nameplate, a heater or an incandescent lamp gives watts. A motor gives horsepower and current, and a transformer gives kVA. The NEC sizes much equipment in volt-amperes because conductors and transformers heat according to the current they carry, not the useful work.

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Why transformers use kVA

A transformer's limit is the heat from its current and the stress from its voltage. Neither depends on what the load does with the power, so the rating is in kVA. A 10 kVA transformer is full at 10 kVA whether the load is heaters at a power factor of 1.0 or motors at 0.8. See transformer kVA.

Common mix-ups

Adding watts and VAR directly. They add as the sides of a triangle, not in a line.
Using 1.732 on single-phase. It belongs only to three-phase.
Thinking reactive power is wasted energy. It is energy exchanged back and forth each cycle. The waste is the heat its extra current makes in the conductors.

On the Texas journeyman exam

Power quantities sit in definitions, theory and plans, 5 scored items across both portions under the PSI bulletin, and underpin load, motor and transformer calculations. Study to convert among watts, volt-amperes and current, single-phase and three-phase.

Practice it

The Ohm's law calculator works the power formulas, including three-phase. Our blog has Ohm's law and power formulas in one place. Every term in this set is in the electrical terms glossary.

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Not affiliated with or endorsed by TDLR, PSI or NFPA. NEC and National Electrical Code are registered trademarks of NFPA.

Sources

Show the list

Candidate Information Bulletin, Texas electricians (updated 9/15/2026), PSI for the Texas Department of Licensing and Regulation.
NFPA 70, National Electrical Code (2026 edition), NFPA. Free read-only access with an account.

Facts checked 26 October 2026 against the sources listed above. If something has changed, tell us and we will correct it within 2 business days.

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