Mike Dolt Enterprises
Mike Dolt Enterprises
User: Chris3585, Location: Smyrna, Georgia
Asked on: Friday, April 1, 2011 at 2:45 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:37 am EDT
Question: I am working on the plans to add an overhead 120/208 volt electrical service to an existing building. The conduits would transition from overhead, through the roof, and to a horizontal wiring trough. The trough would then be tapped (6) times for (5) tenants and a house meter. We are trying to avoid a main service disconnect as this is a large service (2000 amps) and the disconnect is costly. Since the service conductors are unprotected, would this room need to be 3 hour rated (similar to a transformer vault) or could the room be 2 hour rated or does the room even need to be rated at all?Chris
NEC Requirements
According to the National Electrical Code (NEC) 2023: Article 110.26(A)(1)
Service conductors shall be protected against physical damage.
Article 230.70(A)(1)
Overcurrent protection shall not be required for service conductors supplied by a single feeder and protected by the overcurrent device of the service.
3-Hour Rated Room
NEC 2023 Section 110.26(A)(1) does not specifically require a 3-hour rated room for unprotected service conductors. However, it is considered best practice to provide additional protection for large services (more than 1000 amps).2-Hour Rated Room
NEC 2023 does not specify the fire resistance rating of the room where unprotected service conductors are located. However, the following factors should be considered: Local building codes may require a specific fire resistance rating for rooms containing electrical equipment. The location of the room within the building and its proximity to other areas. The potential for fire hazards present in the room.
Unrated Room
If a 2-hour or 3-hour rated room is not required by local codes or other factors, an unrated room may be acceptable. However, the following measures should be taken to minimize the risk of fire: Install the service conductors in a dedicated area with limited access. Use conduit or other enclosures to protect the conductors from physical damage. Install smoke and fire detection systems in the area.
Recommendation
Based on the information provided, I would recommend exploring the following options: 2-hour rated room
This is a reasonable compromise between safety and cost.
Unrated room with additional protection
This option requires careful planning and implementation of protective measures.
Important Note:
Always consult with a qualified electrician and local building officials to ensure compliance with all applicable codes and regulations. Flag for review