Certainly! Let's break down the question and solve it step by step: **Question Restated:** An electrical system that's **not grounded** and is between **120 and 1000 V** must include the use of _______. This question is testing your knowledge of electrical safety requirements, specifically for ungrounded systems within a specified voltage range. --- ## Step 1: Identify the Code Reference The question is based on the **National Electrical Code (NEC)**. The relevant section is **NEC 250.21 and 250.22** (referencing the 2020 NEC, which is widely used as of 2024). --- ## Step 2: Analyze the Voltage Range - **Voltage Range:** 120 V to 1000 V - **System Type:** Not grounded (ungrounded) --- ## Step 3: NEC Requirements for Ungrounded Systems **NEC 250.21(B):** > "Ungrounded systems shall be equipped with a **ground detector**." This means that for ungrounded systems above 120 V (but not exceeding 1000 V), it is required to have a way to detect ground faults, since there is no intentional connection to ground that would allow overcurrent devices to operate if a single line fault occurs. --- ## Step 4: Explanation - **Why is a ground detector needed?** In ungrounded systems, a single ground fault does not cause a circuit breaker to trip, but it creates a dangerous situation. A ground detector system will alert personnel of the first ground fault so corrective action can be taken before a second fault occurs, which could lead to a phase-to-phase short. --- ## Step 5: Final Answer **An electrical system that's not grounded and is between 120 and 1000 V must include the use of a _ground detector_.** --- ### **Summary Table:** | System Voltage | Grounded/Not Grounded | Required Device | |-------------------|----------------------|---------------------| | 120-1000 V | Not grounded | Ground detector | --- ## **Final Answer:** **A ground detector.** **Full sentence:** An electrical system that's not grounded and is between 120 and 1000 V must include the use of a **ground detector**.