How far must the service panel enclosure door be able to open?

The service panel enclosure door must be able to open a full 90 degrees, which is critical for safe and effective access to the electrical components within the panel. This allows for sufficient clearance to inspect and work on circuit breakers or fuses without obstruction.

An opening of 90 degrees ensures that the door does not inhibit access or create a hazard while a technician is performing necessary inspections or repairs. If the door were to open less than this angle, it could restrict maneuverability and make it difficult to work safely. Additionally, adhering to this requirement helps ensure compliance with the National Electrical Code (NEC), which establishes safety standards for electrical installations.

Thus, the correct answer emphasizes the importance of accessibility and safety in electrical panel design and operation.