If you add something that did not previously exits then it's an improvement. If something already exists and it breaks, it's a repair.
Yes, I know that already. But the question is specific to something breaking. The break forced the addition. Why would I add an additional breaker to my home that didn’t need it until the home office. I am under audit and arguing it Is repair because the single breaker couldn’t take the power load. Make sense?
If it broke, then replacing the broken part with the same part would be a repair. If replaced with an upgrade to provide additional power it would be an repair plus an improvement. What it would have cost to just replace the broken breaker can probably be subtracted from the cost of the improvement and deducted as a repair. The remainder would be an improvement added to the cost basis of the property. That is my opinion anyway.
I look at it the same way as if the home office space was not big enough for the inventory so it bulged out a wall in the home and broke a stud. Repairing the broken stud would be a repair. Expanding the office space by added an addition to the home to make it bigger would be a home improvement regardless of what the additional space would be used for or the reason for adding it.