3.1 General Electrical Knowledge

Why This Matters on the Exam

The Virginia Journeyman exam blueprint assigns 3 questions to General Electrical Knowledge — small in raw count but foundational. Every branch-circuit calculation, conductor ampacity lookup, and troubleshooting scenario on the rest of the exam assumes you can distinguish volts from amps and read a meter correctly. Get the units wrong and every downstream answer is wrong.

Units and Quantities

Electrical work is governed by four interrelated quantities. Memorize the unit and its symbol; the exam often uses the symbol without spelling it out.

Volt-amperes (VA) differ from watts when a circuit has reactance: W = VA × power factor. Resistive loads (heaters, incandescent lamps) have W ≈ VA; motors and ballasts do not. The NEC lists many equipment ratings in VA (not W) because the source must supply apparent power regardless of PF. A 1500 VA transformer at 0.8 PF delivers only 1200 W of real work.

Conductors and Insulators

A conductor permits current flow with low resistance — copper, aluminum, or copper-clad aluminum. Per NEC 110.5, conductors must be one of these three materials unless the Code provides otherwise; when a rule does not name the material, the sizes given are based on copper. An insulator resists current flow — thermoplastic, rubber, ceramic. Insulation is rated by temperature (60°C, 75°C, 90°C) and environment (moisture-resistant THWN, sunlight-resistant XHHW-2). Conductor ampacity in Table 310.16 depends on both the metal and the insulation temperature rating: a 12 AWG copper THHN is rated 30 A at 90°C column but only 25 A where the 75°C column applies (terminations limit the usable ampacity).

Exam Terminology You Must Know

• Ampacity — current-carrying capacity of a conductor in amperes, from Tables 310.16–310.20 with correction (temperature) and adjustment (conduit fill) factors applied.
• Voltage drop — reduction in voltage along a conductor due to resistance; NEC recommends ≤3% on branch circuits and ≤5% total (feeder + branch) for reasonable efficiency.
• Continuous load — a load expected to run 3 hours or more (Article 100); branch-circuit conductors and overcurrent devices must be sized at 125% of a continuous load.
• Nominal voltage — the named system voltage (120V, 208Y/120V, 480Y/277V); used for equipment voltage ratings per NEC 110.4.
• AWG — American Wire Gauge; conductor size system per NEC 110.6. Larger gauge number = smaller conductor (14 AWG < 10 AWG < 1/0 AWG). Sizes above 4/0 AWG are expressed in kcmil (thousands of circular mils).

Reading Electrical Drawings

The exam references symbols, not photos. Key conventions:

• One-line diagram — a simplified schematic showing the source, disconnects, overcurrent devices, transformers, and loads in a single line per phase.
• Common symbols: a switch is two triangles touching points; a receptacle is an arc with a dot; a luminaire is a circle with an X; the grounded (neutral) conductor is identified by three horizontal dashes or the letter N.
• Panelboard schedules list circuit number, load description, conductor size, OCPD rating, and phase (A/B/C). A balanced panel spreads loads across phases so the neutral carries only the unbalanced current.

Measurement Tools

Safety note: Verify the meter is rated for the installation category (CAT III or CAT IV for service work) and the voltage present. A CAT II meter applied to a CAT III service can fail catastrophically. Always test the meter on a known live source first, then on the de-energized circuit, then on the live source again — the "live-dead-live" check required by NFPA 70E.

Worked Example: Measuring a Receptacle Circuit

A 120V receptacle reads 118.2V under a 14 A load. The one-way run is 100 ft of 12 AWG copper (≈1.93 Ω/1000 ft from Chapter 9, Table 8). Voltage drop is:

Vd = (2 × L × I × R) / 1000 = (2 × 100 × 14 × 1.93) / 1000 ≈ 5.4 V

That is 5.4 / 120 = 4.5% — over the 3% branch-circuit recommendation, so the run needs a larger conductor (10 AWG, ≈1.21 Ω/kft, gives Vd ≈ 3.4 V or 2.8%). This is the exact kind of reasoning the exam tests: measure, calculate, decide.