What is the minimum rating in amperes for a 480-volt, three-phase, wye-connected feeder disconnect that needs ground-fault protection?

When determining the minimum rating in amperes for a 480-volt, three-phase, wye-connected feeder disconnect that requires ground-fault protection, it's essential to consider the National Electrical Code (NEC) guidelines and standards pertaining to ground-fault protection.

In general, the requirement for ground-fault protection is often linked to the rating of the disconnect or feeder. For three-phase systems, the NEC specifies that ground-fault protection is required for feeders rated at more than a certain amperage. According to the NEC, the minimum rating for a feeder that requires ground-fault protection is typically set beyond the threshold of common ratings to ensure safety and equipment protection.

In this case, a rating of 1000 amperes is commonly required for better protection and compliance with NEC standards. This rating offers a suitable balance between preventing nuisance tripping and ensuring the effective operation of ground-fault protective devices within typical industrial applications.

This means that options below 1000 amperes wouldn’t meet the standard requirements for ground-fault protection in certain applications, making 1000 amperes the correct, minimum rating for the requirement posed in the question.