You're on the right track in trying to address the clearance issue at your disconnect switch. However, attaching a conductive sheet to the fence and grounding it to change the condition might not be the best or safest approach, and might not be compliant with the NEC. Here's why and some alternative solutions

Why Simply Adding a Grounded Sheet Might Not Work (And Could Be Dangerous):
Purpose of Working Clearance

The working clearance requirements in 110.26(A)(1) are in place to protect qualified personnel from electrical hazards while they are inspecting, servicing, or repairing electrical equipment. The distances are based on the voltage to ground and the potential for arc flash. Simply adding a conductive sheet may not sufficiently mitigate these hazards.

Arc Flash Hazard

The primary concern is arc flash. An arc flash can occur if a tool accidentally shorts to ground. The close proximity to a grounded surface like the fence increases the likelihood of this happening. Adding a grounded sheet closer to the equipment, while reducing clearance distance to achieve condition 1, does not inherently reduce the arc flash hazard itself.

Bonding Concerns

You would need to ensure the conductive sheet is properly and reliably bonded to ground. Any breaks or poor connections in the bonding could create a dangerous situation during a fault.

Alternative Solutions (In Order of Preference)


Move the Disconnect or the Fence

This is the most reliable solution and what you should attempt first if possible. Relocate the disconnect switch to meet the required clearance of 3.5 feet. Moving the fence could be another, potentially simpler, option.
2.

Relocate or Enclose the Disconnect Switch

Could the existing disconnect be relocated slightly? Sometimes even a foot of movement is enough. Consider relocating the disconnect switch to a location with better clearance. Can the existing disconnect be enclosed with appropriate barrier so that condition 1 is achieved?3.

Implement Engineering Controls and PPE



Arc Flash Study

Have a qualified electrical engineer perform an arc flash study to determine the hazard levels at the disconnect switch. The study will calculate the incident energy, flash protection boundary, and required personal protective equipment (PPE).

PPE

Implement a comprehensive PPE program based on the arc flash study results. Ensure qualified personnel wear appropriate PPE when working on or near the disconnect switch. This is an essential part of a safe work procedure, but it doesn't replace the need for adequate working clearances.

Training

Provide thorough training to qualified personnel on safe work practices, arc flash hazards, and the proper use of PPE.4.

Seek Variance/Special Permission In very limited circumstances, your local electrical authority may consider a variance or special permission to deviate from the code if you can demonstrate a robust safety plan. This is not a guaranteed option.

Important Considerations



Local Electrical Inspector

Consult your local electrical inspector before making any changes. They have the final say on code compliance and safety. They might have suggestions specific to your situation.

Qualified Personnel

All electrical work must be performed by qualified personnel (licensed electricians) who are familiar with the NEC and local codes.

Documentation

Document all changes and maintain records of inspections, maintenance, and training.

110.26(A)(3) - Entrance to and Egress from Working Space Don't forget the requirement for adequate entrance and egress from the working space.

In Summary:

While your idea of using a conductive sheet to change the condition might seem like a quick fix, it could create unintended hazards and might not be code-compliant. The best approach is to address the root of the problem by either moving the equipment, implementing engineering controls and PPE, or seeking a variance. Always consult with qualified professionals and your local electrical inspector to ensure a safe and compliant solution. Flag for review