18 C.F.R. § 367.81 – Maintenance.

(a) The cost of maintenance chargeable to the various operating expense and clearing accounts includes labor, materials, overheads and other expenses incurred in maintenance work. A list of work operations applicable generally to service company property is included in paragraph (d) of this section. Other work operations applicable to specific classes of property are listed in functional maintenance expense accounts.
(b) Materials recovered in connection with the maintenance of property must be credited to the same account to which the maintenance cost was charged.
(c) Maintenance of property leased from others must be treated as provided in operating expense instruction in § 367.82.
(d) This account must include the following items:
1. (1) Direct field supervision of maintenance.
2. (2) Inspecting, testing, and reporting on condition of property specifically to determine the need for repairs, replacements, rearrangements and changes and inspecting and testing the adequacy of repairs which have been made.
3. (3) Work performed specifically for the purpose of preventing failure, restoring serviceability or maintaining life of property.
4. (4) Rearranging and changing the location of property.
5. (5) Repairing for reuse materials recovered from property.
6. (6) Testing for locating and clearing trouble.
7. (7) Net cost of installing, maintaining, and removing temporary facilities to prevent interruptions in service.
8. (8) Replacing or adding minor items of plant which do not constitute a retirement unit. (See Service Company Property Instruction in § 367.59.)