Fundamental electrical theory tests covering Ohm's Law, circuits, voltage, current, and resistance.
These basic electrical tests cover the theory that everything else in electrical work is built on. Before you can understand why the NEC sizes conductors the way it does, or why motors have overcurrent protection rules, you need to understand the fundamentals: what voltage, current, and resistance are, how they relate to each other, and how circuits behave.
This category is ideal for new apprentices, HVAC students, and anyone who wants to build a stronger foundation before moving into NEC code study. The questions are straightforward — no NEC article lookups needed. You either know the concept or you do not.
Voltage is electrical pressure — the force that pushes electrons through a circuit. Measured in volts. Higher voltage means more force pushing current through the same resistance. Household circuits in the US are 120V or 240V. Three-phase commercial power is 208V, 240V, or 480V.
Current is the flow of electrons — how many electrons pass a point per second. Measured in amperes (amps). More current means more electrons flowing. A 20-amp circuit can push 20 amps of current before the breaker trips.
Resistance is opposition to current flow. Every conductor has some resistance. High resistance means less current for the same voltage. Resistance is measured in ohms. Short circuits have very low resistance — too much current flows, which is why breakers exist.
Ohm's Law ties these together: V = I × R. Knowing any two values lets you calculate the third. This is the most important equation in electrical theory.
The equation V = I × R ties voltage, current, and resistance together — know any two values and you can find the third. Nearly every calculation an electrician does traces back to this.
AC (alternating current) reverses direction 60 times a second in the US; DC (direct current) flows one way only. Most building power is AC, but electronics and batteries run on DC.
Every circuit is built from a small set of components, each doing one job: storing energy, resisting current, or switching it.
Motors, generators, and transformers all rely on the same principle — electromagnetic induction — used three different ways: converting electrical energy to motion, motion to electrical energy, or stepping voltage up or down.
Every circuit needs a way to shut off automatically when something goes wrong — before wires overheat or someone gets shocked.
Beyond theory, electricians need to size conductors correctly, read a wiring diagram, and use test equipment to verify a circuit is safe before energizing it.
Ohm's Law (V = I × R) has three forms — use whichever you need based on what you know:
| Find | Formula | Example |
|---|---|---|
| Voltage (V) | V = I × R | 2A × 60Ω = 120V |
| Current (I) | I = V ÷ R | 120V ÷ 60Ω = 2A |
| Resistance (R) | R = V ÷ I | 120V ÷ 2A = 60Ω |
Power (in watts) tells you how much energy a device uses per second. The formula is P = V × I. A 120V circuit with 10 amps flowing carries 1,200 watts of power. Knowing power helps you size conductors and breakers correctly.
Yes. The journeyman exam tests load calculations (using power and current formulas), motor sizing (using full-load amps), and voltage drop calculations (which combine Ohm's Law with distance and wire size). These all come from basic theory.
DC (direct current) flows in one direction only — like a battery. AC (alternating current) reverses direction many times per second. In the US, AC runs at 60 Hz (60 cycles per second). Most building power is AC. Batteries, solar panels, and some EV charging circuits use DC.
From P = V × I: if power (watts) is the same and voltage doubles, current must halve. That is why large appliances like electric dryers, ranges, and HVAC systems run on 240V — lower current means smaller conductors and less heat generated in the wiring.
Key formulas · NEC articles · Ampacity tables · Exam tips
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