You're asking about a common and practical problem: balancing NEC requirements with efficient distribution of emergency power. Let's break down your scenario and address your concerns

Your Understanding is Generally Correct

Your interpretation of NEC Article 700.10(B) is generally accurate. The key points are: ATS Function

The Automatic Transfer Switch (ATS) is the point where the normal and emergency power sources are separated. This is where the code envisions the transition and source separation happening.

Separation After the ATS

700.10(B)(5)(c) is crucial: "Emergency circuits shall not originate from the same... panelboard enclosure... as other circuits." This is where your concern lies. You cannot have normal and emergency circuits originating from the same panelboard. However, you are not planning to do that. You plan to have a dedicated "EM1" panel fed solely by the emergency system after the ATS.

Feeder to Distribution Equipment

700.10(B)(5)(d) explicitly allows for feeders from the emergency source (in your case, the generator) to distribution equipment (your EM1 panel) before the emergency loads are separated from all other loads. The ATS performs that initial separation.

Your Proposed Solution is Valid

Based on your description, placing the EM1 panel closer to the loads it serves (RTUs, lighting, etc.) after the ATS is entirely compliant with the NEC, provided you follow these key principles:1. Dedicated Emergency Panel

The EM1 panel must only supply emergency loads and must be fed exclusively from the emergency source (generator) via the ATS. No normal power circuits can originate from that panel.2.

Clear Identification

The EM1 panel must be clearly marked as an emergency panel, in compliance with NEC 700.8.
3.

Proper Overcurrent Protection

Emergency circuits must have appropriately sized overcurrent protection, as per NEC Article 240.4.

Wiring Methods (Fire Rating)

This is critical! NEC 700.9(D) and 700.10(D) address fire resistance for emergency circuits. Since your EM1 panel powers equipment like elevators and RTUs (life safety and HVAC), specific rules apply. You will almost certainly need one or more of the following to meet the requirements:

Fire-Resistive Cables

Cables listed for fire resistance (e.g., with an "FH" or "FR" suffix).

Mineral-Insulated (MI) Cable

This is a highly fire-resistant cable type.

Conduit Encased in Concrete

Enclosing the emergency circuit conductors in conduit and then encasing the conduit in concrete.

2-Hour Fire-Rated Enclosure

Locating the EM1 panel within a 2-hour fire-rated enclosure.

Listed Electrical Circuit Protective System

A UL listed system designed to provide fire protection for electrical circuits.The specific requirements for fire resistance depend on the type of occupancy, the height of the building, the location of the circuits (e.g., above or below grade), and whether the emergency circuits pass through areas subject to fire. Consult a qualified electrical engineer and your local AHJ (Authority Having Jurisdiction) for the specific requirements in your area.5.

Voltage Drop

By placing the EM1 panel closer to the loads, you're actively addressing voltage drop concerns, which is a good design practice and enhances the reliability of the emergency system.

In summary, placing the EM1 panel closer to the emergency loads after the ATS is a valid design approach, as long as you adhere to the NEC requirements for separation of normal and emergency power, clear identification, and, most importantly, the fire-resistance requirements for emergency circuits.Recommendations



Consult with a Qualified Electrical Engineer

This is highly recommended. Emergency systems are life-safety critical, and a professional engineer can ensure your design meets all applicable codes and standards. They can perform detailed voltage drop calculations and specify the appropriate wiring methods.

Coordinate with the AHJ

Discuss your design with the local electrical inspector before installation. This can prevent costly rework later. They can clarify any local interpretations of the code and confirm that your design meets their specific requirements.

Document Your Design

Maintain thorough documentation of your emergency system design, including single-line diagrams, panel schedules, and calculations.

Consider Redundancy: Depending on the criticality of the loads, consider adding redundancy to the emergency system, such as multiple emergency panels or backup generators.By following these guidelines and working with qualified professionals, you can create a reliable and code-compliant emergency power system. Flag for review