You're right to be cautious about this setup. While 225.30 might seem to allow it at first glance, there are significant considerations that make this a potentially problematic and likely non-compliant design under a strict code interpretation. Let's break it down

225.30 - Number of Supplies
This section allows one feeder to a detached building. It also allows additional feeders or branch circuits for specific purposes as outlined in 225.30(A) through (E). 225.30(A) covers fire pumps. 225.30(B) covers emergency systems 225.30(C) covers legally required standby systems 225.30(D) covers optional standby systems. 225.30(E) covers One additional supply permitted for the sole purpose of control of the controlled load of a load management systemWhy the Proposed UPS Feed Likely Fails Code


UPS Systems as Standby/Emergency

The key problem is that the intended use of the UPS feed strongly influences whether it's permissible. If the UPS is intended to provide power during utility outages (which is the typical function), it falls into one of the standby categories (legally required or optional - likely optional). If it is an optional standby system, the only way to have another power source to the structure would be for load management. However, the air conditioner would not fall under load management.2.

Double Jeopardy from UPS

It is extremely likely that a UPS cannot be used for load management of an optional standby system. Thus the only compliant design would be to use a transfer switch to feed the entire detached structure.3.

Improperly Sized OCPD Using a 225A rated conductor (which would likely be a 4/0 CU or 250AL) to feed a structure that is protected by a 60 amp breaker is an overload waiting to happen.4. Grounding/Bonding Complexity

Multiple sources introduces complex grounding and bonding considerations. You must maintain a single point of grounding at the detached structure. The two sources must have their equipment grounding conductors (EGCs) bonded together at the detached structure's grounding electrode. This can be confusing and easily missed during installation, leading to safety hazards.5.

Overcurrent Protection

You must ensure that the OCPD feeding the UPS is of sufficient size that the UPS load plus the A/C load is less than the OCPD.6.

Safety Concerns

Having separate panels, one UPS-fed and one not, introduces the potential for accidental contact between circuits from different power sources, creating a shock hazard. Technicians working on the detached structure might not realize that there are two power sources to disconnect.

Why a Load Shed Device is Better



Simplicity

A load shed device avoids the complexities of multiple power sources and panels.

Safety

It's much easier to understand and maintain a single feed with a load-shedding system.

Compliance

It's much easier to ensure compliance with NEC grounding and bonding requirements with a single feed.

Cost-Effectiveness

Depending on the size and complexity of the UPS, a load shed system can be more cost-effective.

Justification to Reject the UPS Feed

Based on the intended use of the UPS, you have strong justification to reject this setup:1.

Code Compliance

The proposed setup likely violates the spirit and possibly the letter of NEC 225.30, especially regarding the permitted number of feeders/circuits.
2.

Safety

The multiple source configuration introduces increased safety risks, including shock hazards and potential for improper grounding and bonding.3.

Complexity

The system is more complex to install, maintain, and troubleshoot compared to a simpler load shed solution.

Recommendations


Advocate for the Load Shed Device

Clearly explain the advantages of a load shed device in terms of simplicity, safety, and code compliance.2.

Consult with an Electrical Engineer

Have an electrical engineer review the load calculations, UPS specifications, and the NEC requirements for the specific application. They can provide a documented and code-compliant design.3.

Discuss Alternatives: If a full UPS backup of the entire detached structure is critical, consider a properly sized UPS with an automatic transfer switch that disconnects the utility feed and connects the UPS output to the entire panel in the detached structure during an outage. This is the most straightforward and often safest approach.In summary, while technically 225.30 might seem to allow it under specific, narrowly defined conditions, the practical and safety considerations strongly suggest that the proposed dual-feed setup with the UPS is a bad idea and likely not compliant. A load shed device or a single-feed UPS with a transfer switch are much better and safer alternatives. Flag for review