Yes, based on typical interpretations of the NEC (National Electrical Code), you will likely need a new service disconnect between the meter and the ATS if the ATS is installed outside. Here's a breakdown of why

NEC Concerns and Rationale:
Service Disconnect Location (NEC 230.70(A)(1))

The NEC requires the service disconnecting means to be readily accessible and located either inside or outside the building nearest the point of entrance of the service conductors. The key is "nearest the point of entrance."

Why this matters

The purpose is to allow firefighters or emergency personnel to quickly and safely de-energize the entire building in case of an emergency.

ATS as a Service Disconnect

An ATS, while capable of switching between sources, isn't automatically considered a service disconnect.

Service Entrance Conductors Outside (NEC 230.6)

Service conductors (the wires between the service point and the service disconnect) are subject to specific rules when run outside the building. They need to be protected from physical damage and often need to be installed in rigid metal conduit (RMC) or intermediate metal conduit (IMC). Minimizing the length of unprotected service conductors outside is a safety best practice.

Applying it to your scenario

1. The meter disconnect is outside. That's fine.
2. The existing service disconnect is inside.3. You're proposing to put the ATS outside, and after the meter disconnect and before the existing service disconnect.4. The ATS, if not acting as the service disconnect, means the service conductors now run outside the building to the ATS, then back into the building to the original service disconnect. This likely violates the principle of the service disconnect being nearest the point of entry.

Why you need a new service disconnect

Because the ATS is located outside the building, it has now changed your service entrance. To comply with the NEC, you will need to install a new service disconnect on the outside of the building, directly before the ATS. The service conductors running from the meter to this new service disconnect will need to follow the rules for service entrance conductors, including appropriate protection. This new service disconnect will serve as the main disconnect for the building and allow for safe and quick power shutoff in case of an emergency.

Common Solutions and Considerations


Install a Service-Rated ATS

The ATS itself can be rated as a service disconnect. A "service-rated" ATS is specifically designed and listed to meet the requirements of a service disconnect. It will have appropriate overcurrent protection (fuses or a circuit breaker) and a clearly labeled handle for shutting off all power to the building. This is often the most practical solution.2.

Install a Separate Service Disconnect

Install a separate, non-ATS service disconnect ahead of the ATS (between the meter and the ATS) on the exterior of the building.3.

Keep ATS Inside

The simplest solution, if possible, is to locate the ATS inside the building near the existing service disconnect.

Important Considerations



Local Amendments

Always check with your local electrical inspector or building department. They may have local amendments to the NEC that affect this installation.

Utility Requirements

The utility company may have specific requirements for the location of the service disconnect and metering equipment. Coordinate with them early in the planning process.

Short-Circuit Current Rating (SCCR)

Ensure that all equipment (ATS, disconnects, and downstream panels) have an appropriate SCCR rating for the available fault current at the service entrance.

In summary, while an ATS is a great solution for backup power, adding it outside typically necessitates a new service disconnect to maintain code compliance and ensure safety. Consult with a qualified electrician and your local authorities to determine the best and most compliant approach for your specific project. Flag for review