Journeyman Electrician Exam (NEC)Services, Feeders, and Branch CircuitsEasy
A commercial building has a 480Y/277V, 3-phase, 4-wire service. The main service disconnecting means consists of six circuit breakers in a single enclosure. What is the maximum number of disconnecting means permitted for a single service?
- AFour
- BSix
- CTwo
- DEight
Show answer & explanationAnswer & explanation
Correct answer: B. Six
According to NEC 230.71(A), the service disconnecting means for each service shall consist of not more than six switches or six circuit breakers mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard or panelboard.
Why the other options are wrong
- A. Four is less than the maximum permitted by the NEC.
- C. Two is too few; the NEC allows more.
- D. Eight exceeds the maximum number permitted by the NEC.
Maximum Service Disconnecting Means
The NEC limits the number of individual service disconnecting means to a maximum of six for a single service, whether in one enclosure or a group of enclosures.
- NEC 230.71(A) specifies the limit.
- Applies to switches or circuit breakers.
- Can be in a single enclosure or a group.
Memory trick: Six switches stop the service, keeping it safe and divisible.