CSLB C-10 Electrical ContractorEquipment and InstallationEasy
A commercial building has a 400-ampere, 208Y/120-volt service. The design calls for a main service disconnect and two sub-panels, each with its own main breaker. The service conductors are run in EMT conduit. How many readily accessible service disconnects are permitted at this location?
- A3
- BUp to 6
- C2
- D1
Show answer & explanationAnswer & explanation
Correct answer: B. Up to 6
NEC 230.71(A) permits a maximum of six disconnect switches or six circuit breakers grouped in a single location to serve as the main service disconnect for a building or structure. The main service disconnect and the two sub-panel main breakers total three disconnects, which is within the permissible limit of six.
Why the other options are wrong
- A. Three disconnects are permitted, but up to six are allowed.
- C. Two disconnects are permitted, but up to six are allowed.
- D. A single disconnect is common, but up to six are permitted.
Six-Disconnect Rule
The National Electrical Code (NEC) permits a maximum of six service disconnects, grouped in a single location, to disconnect all ungrounded conductors from the service-entrance conductors.
- Applies to service disconnects, not branch circuit breakers.
- Disconnects must be grouped in one readily accessible location.
- Each disconnect must clearly indicate the load it controls.
Memory trick: Six Disconnects: 'S'afety 'S'tarts 'S'imply 'S'ix 'S'witches 'S'ecure.