18 C.F.R. § 367.23
When a service or construction is performed for non-associate companies at an amount other than cost, the amount of revenues in excess or deficiency of the cost on servicing the non-associate companies must be charged to account 458.4, Excess or deficiency on servicing non-associate utility companies (§ 367.4584 ) . A deficiency incurred in a project deemed beneficial to the associate companies may be charged to associate companies subject to disallowance by a State Commission or Federal Commission having jurisdiction over the rates or services of the associate companies. To the extent not charged, or if disallowed, the deficiency will be charged to account 458.4 (§ 367.4584 ) . In computing charges to associate companies for any calendar year, any net credit in this account must be deducted from amounts reimbursable by associate companies as compensation for use of capital invested in the service company.
18 C.F.R. §367.23