| 700 / | HD | DATA PROCESSING: GENERIC CONTROL SYSTEMS OR SPECIFIC APPLICATIONS |
| 90 | DD | SPECIFIC APPLICATION, APPARATUS OR PROCESS {16} |
| 286 | DD | .~ Electrical power generation or distribution system {5} |
| 297 | DD | .~.~ Power supply regulation operation {1} |
| 298 | | .~.~.~ By voltage regulation |