You've highlighted a critical area where NFPA 110 requires careful interpretation, especially concerning outdoor installations. Let's break down the relevant clauses and apply them to your specific scenario

Understanding the NFPA 110 Clauses
7.2.
2.2

This clause allows EPSS equipment to be installed within the EPS enclosure. This refers to the generator, transfer switches, and related components being physically located within a generator enclosure or a dedicated room for the EPS (Emergency Power Supply).

7.2.3

This is the key clause in your question. It prohibits installing EPSS equipment in the same room with normal service equipment if that normal service equipment meets the voltage and amperage thresholds (>=150V and >=1000A). The reasoning is to protect the EPSS from potential damage or interruption due to failures within the normal service equipment.

Applying NFPA 110 to Your Outdoor Scenario

The critical question is whether "room" applies to outdoor installations. NFPA 110 doesn't explicitly define "room" in this context, leading to interpretation. However, here's a breakdown of how to approach this:1. "Room" and Outdoor Spaces

While a literal interpretation of "room" might suggest only enclosed spaces, the intent behind 7.2.3 is to mitigate risk from a normal service equipment failure. An outdoor pad-mounted transformer and switchboard could pose a similar risk to nearby EPSS equipment as equipment within an enclosed room. Arc flash and physical damage from a transformer failure can extend beyond the immediate vicinity of the equipment.2.

The Intent Behind 7.2.3

The enhanced content reinforces that the purpose of 7.2.3 is to protect the EPSS from high arc-fault energy or physical damage emanating from the normal service equipment. Arc flash events can damage sensitive electronic components in the EPSS, and a catastrophic transformer failure could cause structural damage.
3.

Separation vs. Distance

The standard doesn't explicitly call out a physical barrier / wall but calls for a physical separation. A physical separation implies there must be some sort of method to ensure the EPSS is safe.4.

Authority Having Jurisdiction (AHJ)

This is the most crucial point. You must consult with the AHJ. The AHJ has the final say on interpreting NFPA 110 and determining what constitutes sufficient separation in your specific outdoor context.

Recommendations

Considering the intent of NFPA 110 and the potential hazards, here's a recommended approach: Consult the AHJ

Discuss your proposed outdoor installation with the local AHJ (fire marshal, building inspector, etc.). Present your plans, highlighting the distances between the pad-mounted transformer/switchboard and the EPSS equipment. Ask for their interpretation of 7.2.3 in this outdoor scenario and what they deem adequate separation.

Risk Assessment

Conduct a risk assessment focusing on potential failure modes of the pad-mounted transformer and switchboard. Consider arc flash hazards, physical damage from explosions, and the potential impact on the EPSS equipment. Document your findings.

Mitigation Options

Explore potential mitigation strategies to present to the AHJ. These could include:

Increased Distance

Maximizing the distance between the normal service equipment and the EPSS equipment. The risk assessment should inform how much distance is necessary.

Physical Barrier

Constructing a robust, fire-rated wall or barrier between the equipment. This is likely the most conservative approach and might be required by the AHJ. The wall should be designed to withstand potential explosions or projectile hazards.

Blast-Resistant Enclosures

Enclosing the pad-mounted transformer and switchboard in a blast-resistant enclosure to contain any explosions.

Strategic Placement

Orienting the equipment so that any potential blast or arc flash is directed away from the EPSS equipment.

Engineering Study

Hiring a qualified engineer to conduct an arc flash study and recommend appropriate separation distances and protective measures.

In summary: While NFPA 110 doesn't explicitly mandate a wall in your outdoor scenario, the intent of the standard is to protect the EPSS from hazards associated with the normal service equipment. The AHJ will ultimately determine if the proposed separation is sufficient. A risk assessment and a willingness to explore mitigation options will be crucial in reaching a compliant solution. A physical separation would be expected, given the language in the standard. Flag for review