Journeyman Electrician Exam (NEC)Services, Feeders, and Branch CircuitsEasy
A residential dwelling unit has a total calculated load of 12,500 VA. What is the minimum standard ampere rating for the main overcurrent device, according to NEC 240.6(A)?
- A150 Amperes
- B100 Amperes
- C60 Amperes
- D125 Amperes
Show answer & explanationAnswer & explanation
Correct answer: B. 100 Amperes
For a dwelling unit with a calculated load of 12,500 VA, the minimum service disconnecting means rating is 100 amperes, as per NEC 230.79(C). NEC 240.6(A) lists standard ampere ratings for overcurrent devices. A 100A main breaker is the smallest standard rating meeting this requirement.
Why the other options are wrong
- A. 150 Amperes is a standard rating but not the *minimum* required for this load.
- C. 60 Amperes is too small for a 12,500 VA dwelling unit load.
- D. 125 Amperes is a standard rating but not the *minimum* required for this load.
Minimum Service Disconnect Rating (Dwelling)
For a one-family dwelling, the service disconnecting means must have a rating of not less than 100 amperes, 3-wire, for a calculated load of 10 kVA or more.
- Applies to one-family dwellings.
- Minimum 100A, 3-wire.
- Triggered by calculated load of 10 kVA (10,000 VA) or more.
Memory trick: Home's main power needs a hundred-amp hero.