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. What is the required ampacity of the main bonding jumper at the service for a 200-ampere service? → It must be sized per NEC Table 250.66 based on service conductor size
2. Using NEC guidelines, what is the maximum recommended voltage drop for a feeder circuit? → 3%
3. Kirchhoff's Voltage Law (KVL) states that: → The algebraic sum of all voltages around any closed loop equals zero
4. What action is required when a splice is made in a branch circuit conductor inside a conduit? → The splice must be enclosed in an accessible junction box
5. Which NEC section governs the maximum number of receptacles permitted on a 15- or 20-ampere branch circuit in a commercial occupancy? → NEC does not limit the number; load calculations govern
6. When is it permitted to connect the neutral bar and ground bar together in a subpanel? → Never — neutral and ground must always be separate in subpanels
7. Per NEC 110.15, what color must be used to permanently identify the high-leg conductor in a 4-wire delta system? → Orange
8. According to NEC 110.5, what is the default conductor material when the Code references conductors without specifying the metal? → Copper
9. What type of transformer is designed to make small voltage adjustments, typically within ±5–20% of the supply voltage? → Buck-boost transformer
10. What is the minimum headroom required above the working space for electrical panelboards supplying branch circuits in commercial occupancies? → 6.0 feet (1.8 m) or the height of the equipment, whichever is greater
11. What is the standard ampacity of a #12 AWG copper conductor with THHN insulation in a conduit with three current-carrying conductors? → 20 amperes
12. What is the minimum burial depth for rigid metal conduit (RMC) under a parking lot? → 12 inches
13. A conductor carrying current is placed in a magnetic field. The resulting force on the conductor is described by: → The Left-Hand Rule (motor action)
14. NEC 110.26(C)(2) requires two entrances/exits from working spaces around electrical equipment under what condition? → Equipment rated 1200 amperes or more and over 6 feet wide
15. What color is an electrical grounding conductor permitted to be? → Green
16. Per NEC 220.87, what is the required minimum period of recorded demand data needed to use the optional method for determining existing loads? → 30 days
17. Which type of motor starter uses reduced voltage to limit inrush current during starting? → Autotransformer starter
18. 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
19. A 20-ampere, 125-volt receptacle outlet is required in which of the following bathroom locations per NEC? → Within 3 feet of the sink basin
20. A 480V, 3-phase service supplies a 75 kVA transformer and a 60-ampere motor load. The transformer load in amperes on the 480V side is approximately: → 104 amperes
21. A motor nameplate shows a service factor of 1.15. What does this mean? → The motor can operate continuously at 115% of its rated load
22. For a grain storage elevator, the area within 3 feet of any opening in a belt or bucket elevator housing is classified as: → Class II, Division 1
23. Which wiring method is specifically prohibited in theaters for use above the stage? → Type NM cable
24. A 20A, 120V branch circuit supplies a single receptacle. The cord-and-plug-connected load must not exceed what amperage for continuous operation? → 16A
25. Which conductor is used to bond the structural steel of a building to the grounding electrode system? → Grounding electrode conductor
26. Which standard governs the safety requirements for electrical installations in the United States and is the basis for most state and local electrical codes? → NFPA 70 (NEC)
27. In a delta (Δ) connected 3-phase system, the relationship between line current and phase current is: → IL = Iφ × √3
28. According to NEC 110.26(B), what is the minimum width of the working space in front of electrical equipment? → The width of the equipment or 30 inches, whichever is greater
29. A variable frequency drive (VFD) controls motor speed primarily by varying the: → Supply frequency and voltage supplied to the motor
30. How many 15-ampere, 120-volt branch circuits are required per NEC for general lighting in a 2,400 sq ft dwelling unit using a 3 VA/sq ft load? → 3 circuits