The utility shall adjust its estimate of construction costs to reflect the costs that are actually incurred. Upon completion of an installation which differs from the utility's original cost estimate, a recalculation of the customer contribution shall be made using the same method as was used to determine the original contribution. If said recalculation differs by more than $20 from original estimate, a refund or additional billing shall be rendered to the customer.
Wis. Admin. Code Public Service Commission PSC 113.1009