Electrician's Licensing Practice Exam

When using 500 MCM, what ground wire sizes are appropriate on a 400-amp service?

1. 250MCM or 300MCM

2. 350MCM or 400MCM

3. 500MCM or 600MCM

4. 200MCM or 225MCM

The correct answer is: 350MCM or 400MCM

To determine the appropriate ground wire sizes for a 400-amp service using 500 MCM conductors, it is essential to adhere to the National Electrical Code (NEC) guidelines, specifically Table 250.122, which outlines the requirements for equipment grounding conductors based on the rating of the overcurrent device. For a 400-amp service, the NEC stipulates that the minimum size for the equipment grounding conductors should be either 350 MCM or 400 MCM. These sizes ensure that the ground wire can handle potential fault currents safely while providing adequate protection for the equipment and ensuring the safety of those who may come into contact with the electrical system. The suitability of these sizes is also based on their ability to efficiently carry ground fault currents back to the source, reducing the risk of shock or fire hazards. Therefore, selecting either 350 MCM or 400 MCM corresponds directly to the requirements set forth by the NEC for a 400-amp service. Adhering to these standards is crucial for compliance and safety in electrical installations.