For a one-family dwelling, the service disconnecting means shall have a rating of not less than ___ amps, 3-wire.

• A. 30
• B. 60
• C. 100
• D. 150

Answer: (C)

The main idea is sizing the service disconnect to handle the expected service current for a dwelling. For a one-family dwelling with a 120/240 V, three-wire service, the minimum rating for the service disconnecting means is 100 amps. This ensures the disconnect can safely interrupt the fault current and accommodate typical loads for a single-family home. A 30-amp or 60-amp disconnect would be undersized for typical dwelling demand, while 150 amps is permissible but is not the minimum required. Thus, 100 amps is the correct minimum.