IEC Study Guide 2026
Everything you need to pass the IEC exam in one place: the exam format, every topic to study, real practice questions with explanations, flashcards, and full-length practice tests. Free, no sign-up needed.
📋 IEC Exam Format at a Glance
📚 IEC Topics to Study (15)
✍️ Sample IEC Questions & Answers
1. 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), also known as Locked-Rotor Amps (LRA), is the inrush current drawn by a motor at startup when the rotor is stationary ('locked'). This current is typically 6 to 8 times the motor's normal full-load current and is a critical value for sizing short-circuit protection and motor controllers.
2. When installing a feeder to a detached garage with its own subpanel, which practice is critical for safety?
In a subpanel located in a separate building, the grounded (neutral) conductor and the equipment grounding conductor must be kept separate. A separate equipment grounding conductor must be run with the feeder conductors to provide the effective ground-fault current path back to the main service. Bonding the neutral and ground at the subpanel would create objectionable current on the grounding conductors. A grounding electrode system is also required at the detached structure.
3. 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?
Explanation: A 20-amp circuit breaker is the largest that can be installed on a 12 AWG copper circuit conductor. This is in accordance with the National Electrical Code (NEC) regulations for circuit protection, ensuring that the circuit is adequately protected from overcurrent conditions while using 12 AWG copper conductors.
4. At a marina, what is the maximum ground-fault protection (GFP) setting permitted for the main overcurrent device supplying a dock where shore power is provided to boats?
NEC 555.35(A)(3) requires that feeder and branch-circuit conductors installed on docking facilities be provided with ground-fault protection of equipment (GFPE) set to open at currents not exceeding 100 mA. Receptacles providing shore power have a lower 30 mA requirement.
5. A 45 kVA, single-phase, 240V/120V transformer is operating at full load. What is the rated primary current?
Primary rated current = kVA × 1,000 ÷ primary voltage = 45,000 ÷ 240 = 187.5A.
6. Which of the following is NOT a primary function of an Equipment Grounding Conductor (EGC)?
The Equipment Grounding Conductor (EGC) is a safety conductor and should only carry current during a ground-fault condition. The grounded conductor (neutral) is the conductor designed to carry the unbalanced current in a circuit during normal operation.