into the same structure per the National Electrical Code. Only exception is for different voltages, etc.
Every building has some electrical switchgear that constitutes a "single point of failure", and it is mandated to do so by code. Simplifies cutting off power by first responders in an emergency, etc.
Buss duct is generally not stocked by local distributors, and may have been custom made to order (angle/offsets/termination sections anyway) so depending on what exactly burned up, they could be a while sourcing replacement parts.