IEC Cheat Sheet 2026

The 30 highest-yield IEC facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. Per NEC 110.15, what color must be used to permanently identify the high-leg conductor in a 4-wire delta system? → Orange
2. What type of transformer is designed to make small voltage adjustments, typically within ±5–20% of the supply voltage? → Buck-boost transformer
3. What color is an electrical grounding conductor permitted to be? → Green
4. What is the smallest allowable AWG size for copper THHN/THWN conductors used in underground conductors for a 125-amp, 120/240-V, 3W residential service? → 2 AWG copper
5. A 45 kVA, single-phase, 240V/120V transformer is operating at full load. What is the rated primary current? → 187.5A
6. What is the maximum amp rating for a circuit breaker that can be installed on a 12 AWG copper circuit conductor connected to multiple receptacles? → 20-amp
7. How much is allowed for each branch circuit serving laundry receptacles when calculating residential service load? → 1,500 volt-amperes
8. Which of the following is NOT a primary function of an Equipment Grounding Conductor (EGC)? → To carry the unbalanced neutral current during normal circuit operation.
9. Under what condition does OSHA permit a qualified person to work on or near exposed energized parts without de-energizing the circuit? → When de-energizing introduces additional or increased hazards.
10. When installing insulated equipment grounding conductors of size 6 AWG or smaller, what color(s) must the conductor's continuous outer finish be? → Green or green with one or more yellow stripes
11. A 25 kVA, single-phase, 480V/240V transformer is operating at full load. What is the approximate rated secondary current? → 104A
12. According to NEC 110.26(A), what is the minimum required width of the working space in front of an electrical panelboard that is 24 inches wide? → 30 inches
13. According to NEC 450.3(B), a 480V transformer with a rated primary current of 9A requires primary overcurrent protection not exceeding what value? → 15A
14. What is the primary purpose of tap connections on a transformer's primary winding? → To adjust the voltage ratio for variations in supply voltage
15. In a commercial installation, a metallic cable tray is used to support various power and control cables. To comply with NEC Article 392, the cable tray must be: → Bonded and connected to an effective equipment grounding conductor.
16. How many kilowatt-hours (kWh) will the utility bill for if a 60-watt lamp operates continuously for 21 hours? → 1.26 kWh
17. Which three-phase transformer connection provides a neutral conductor on the secondary side? → Delta-Wye
18. When connecting two single-phase transformers in parallel, which of the following is NOT a requirement for proper parallel operation? → Identical kVA ratings
19. Which of the following is NOT a standard ampere rating for a fuse or inverse time circuit breaker according to NEC® 240.6(A)? → 120A
20. How many feet should an extension ladder extend above the top of a building to ensure proper safety and be securely anchored? → 3 feet
21. What is the minimum depth requirement for installing underground feeder cable in PVC conduit under a building? → At least 0 inches deep
22. Which of the following is a primary function of a motor controller, as defined by the NEC? → To start and stop the motor, and interrupt the locked-rotor current.
23. According to NEC Article 300, which of the following is an unacceptable method for supporting raceways in a commercial building with a suspended ceiling? → Attaching raceway supports directly to the suspended-ceiling grid.
24. What should be minimized to reduce conductor insulation damage and arcing damage to electrical equipment during a ground fault or short circuit? → The time duration of the fault should be minimized.
25. The current a motor draws at the instant of starting when full voltage is applied, before the rotor begins to turn, is known as what? → Locked-Rotor Current (LRC)
26. What is the primary purpose of a K-rated transformer? → To handle harmonic currents from non-linear loads
27. Which of the following BEST describes the function of 'supplementary overcurrent protection' as defined by the NEC®? → It is used in addition to a branch-circuit OCPD for specific equipment protection.
28. What type of switch will be used to break two underground circuit conductors such as to a motor? → A double-pole switch
29. A 480V/120V step-down transformer supplies a 2,400W load at 120V. What is the approximate primary current drawn from the 480V supply, assuming 100% efficiency? → 5A
30. According to NEC 450.11, which of the following information is required on a transformer nameplate? → Rated kVA, frequency, and primary and secondary voltages