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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 ā€” free, no sign-up.

80 questions
240 min time limit
70.00% to pass
  1. What is the required ampacity of the main bonding jumper at the service for a 200-ampere service? ā†’ 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? ā†’ 3%
  3. Kirchhoff's Voltage Law (KVL) states that: ā†’ 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? ā†’ 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? ā†’ 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? ā†’ Never ā€” 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? ā†’ Orange
  8. According to NEC 110.5, what is the default conductor material when the Code references conductors without specifying the metal? ā†’ Copper
  9. What type of transformer is designed to make small voltage adjustments, typically within Ā±5ā€“20% of the supply voltage? ā†’ Buck-boost transformer
  10. What is the minimum headroom required above the working space for electrical panelboards supplying branch circuits in commercial occupancies? ā†’ 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? ā†’ 20 amperes
  12. What is the minimum burial depth for rigid metal conduit (RMC) under a parking lot? ā†’ 12 inches
  13. A conductor carrying current is placed in a magnetic field. The resulting force on the conductor is described by: ā†’ 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? ā†’ Equipment rated 1200 amperes or more and over 6 feet wide
  15. What color is an electrical grounding conductor permitted to be? ā†’ 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? ā†’ 30 days
  17. Which type of motor starter uses reduced voltage to limit inrush current during starting? ā†’ 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? ā†’ 2 AWG copper
  19. A 20-ampere, 125-volt receptacle outlet is required in which of the following bathroom locations per NEC? ā†’ 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: ā†’ 104 amperes
  21. A motor nameplate shows a service factor of 1.15. What does this mean? ā†’ 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: ā†’ Class II, Division 1
  23. Which wiring method is specifically prohibited in theaters for use above the stage? ā†’ 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? ā†’ 16A
  25. Which conductor is used to bond the structural steel of a building to the grounding electrode system? ā†’ 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? ā†’ NFPA 70 (NEC)
  27. In a delta (Ī”) connected 3-phase system, the relationship between line current and phase current is: ā†’ IL = IĻ† Ɨ āˆš3
  28. According to NEC 110.26(B), what is the minimum width of the working space in front of electrical equipment? ā†’ The width of the equipment or 30 inches, whichever is greater
  29. A variable frequency drive (VFD) controls motor speed primarily by varying the: ā†’ 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? ā†’ 3 circuits
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