Under 230.95, the rating of the service disconnecting means is the rating of which component?

• A. The rating of the largest fuse that can be used
• B. The rating of the largest load that can be connected
• C. The voltage rating of the equipment
• D. The horsepower rating of the service

Answer: (A)

The rating of a service disconnecting means is determined by the maximum overcurrent protection that can protect the service conductors feeding the building. In practice, that protective device is a fuse (or main overcurrent device), so the disconnect must be rated at least as high as the largest fuse that can be used on those conductors. This ensures the disconnect can safely interrupt the same fault current that the protection devices could allow. The other factors—the load’s size, the equipment’s voltage rating, or motor horsepower—don’t set the disconnect’s rating.