Master Electrician Practice Exam

What is the minimum size 75º C copper service-entrance conductors required for a 200 ampere rated commercial service?

1. 2/0 AWG

2. 3/0 AWG

3. 4/0 AWG

4. 1 AWG

The correct answer is: 3/0 AWG

To determine the minimum size of copper service-entrance conductors for a 200 ampere rated commercial service, it is necessary to refer to the National Electrical Code (NEC) standards, particularly Table 310.15(B)(16) for conductors in different temperature insulation ratings. For 75º C rated conductors, the NEC specifies that a conductor needs to be large enough to handle the continuous load without overheating. For a 200 ampere service, the code indicates that a minimum conductor size of 3/0 AWG copper is required when using conductors rated for devices at 75º C. Choosing 3/0 AWG ensures that the wire is capable of safely carrying the current without exceeding the acceptable temperature rating, thus providing a safe and compliant setup. If smaller gauges were selected, they would not adequately handle the expected load, potentially leading to overheating and associated risks. Therefore, selecting 3/0 AWG copper conductors aligns with best practices for safety and reliability in electrical installations for a 200 ampere service.