I see a few options from an installers view.

1) Replace the gear, continue as planed.

2)Do not touch the gear or the transformers, have the power co bring in a second service with it's own transformer to power the addition. (AHJ can allow it)

3)Replace the old 1600 amp gear with a new 2500 amp gear and feed both buildings from this new gear.

4)Bring the service to the addition and feed the original 50 year old gear from the additions service. This would add impedance to the circuit ahead of the old gear.

Anyway you want to go we would be happy to do the work, lots of gear and copper. [Linked Image]

Bob

Bob Badger
Construction & Maintenance Electrician
Massachusetts