Okay, let's break down NEC 225.31 and 225.32 and how they apply to your situation.

Understanding NEC 225.31 & 225.32 NEC 225.31 (General)

Requires a disconnecting means for outside feeders and branch circuits at the building or structure they supply. This is a general rule ensuring you can easily de-energize the power to that building.

NEC 225.32 (Location)

The disconnecting means must be located at a readily accessible location either outside the building or structure or inside nearest the point of entrance of the conductors.

NEC 225.32 Exception 1

This is the crucial exception for your scenario. It states:> Exception No. 1: Where documented safe switching procedures are established and maintained for disconnection of the feeder or branch circuit, the disconnecting means shall be permitted to be located elsewhere on the premises.
Applying the Code to Your Situation

Here's an analysis of your setup:1. Your Electrical Building is a "Building or Structure"

NEC 225 applies because your electrical building is a separate structure being fed from another location.2.

The 300' Distance Matters

The 300-foot distance between the transformer/transfer switch and the electrical building is why 225.31 and 225.32 are in play. You need a disconnect at or near the electrical building.3.

The Primary Service Disconnect Doesn't Qualify

The disconnect on the primary side of the transformer does not meet the requirements of 225.32. It doesn't disconnect the secondary conductors feeding the electrical building.4.

The Disconnect Before the Transfer Switch is Key

The disconnect on the supply side of the transfer switch is the most important part of your question. If that disconnect truly isolates all power to the feeder going to the electrical building, then it potentially meets the requirements of 225.32

IF you can use Exception 1.

Does the Disconnect Before the Transfer Switch Qualify Under Exception 1?

This is where it gets tricky, and requires careful consideration: Documented Safe Switching Procedures

You state you have documented procedures and LOTO. This is a critical requirement for using Exception 1. However, the procedures must be very specific and demonstrably effective. They should include: A detailed step-by-step process for identifying and safely isolating the specific feeder to the electrical building. Verification that the feeder is de-energized after the disconnect is opened and locked out. Training requirements for personnel who perform the switching. Regular reviews and updates to the procedures.

"Elsewhere on the Premises"

The disconnect before the transfer switch is indeed "elsewhere on the premises" relative to the electrical building.

Complete Isolation

The disconnect must isolate all ungrounded conductors feeding the electrical building. If there are any other sources of power (e.g., a separate generator, a connection to another electrical system), Exception 1 cannot be used unless your documented procedures account for all potential sources.

In Summary



Potentially, YES, the disconnect on the supply side of the transfer switch could qualify as the disconnecting means for the electrical building under NEC 225.32 Exception 1. However, this is heavily dependent on the adequacy of your documented safe switching procedures. It is crucial that the disconnect on the supply side of the transfer switch opens ALL ungrounded conductors feeding the electrical building. AHJ Approval is Recommended

The interpretation and acceptance of Exception 1 often depend on the local Authority Having Jurisdiction (AHJ). I strongly recommend discussing your specific setup and procedures with the AHJ before relying on Exception 1. Get their written approval if possible.

Recommendations


Review and Improve Procedures

Critically examine your documented safe switching procedures. Make sure they are extremely clear, detailed, and specifically address the feeder to the electrical building. Consider adding extra layers of verification (e.g., voltage testing) to ensure complete de-energization.2.

Consult with an Electrical Engineer

Engage a qualified electrical engineer to review your system and your procedures. They can provide an independent assessment and ensure compliance with the NEC.3.

Consider an Additional Disconnect

If there's any doubt about the adequacy of your procedures, or if the AHJ is hesitant, the simplest and most compliant solution is to install a disconnect switch at the electrical building itself. This eliminates any reliance on Exception 1.4.

Labeling

Regardless of whether you rely on Exception 1 or install a new disconnect, ensure clear and permanent labeling at both* the disconnect and the electrical building, indicating the location of the disconnecting means and the equipment it serves.

Disclaimer: I am an AI chatbot and cannot provide professional engineering or legal advice. This information is for educational purposes only. Consult with qualified professionals for your specific situation. Flag for review