| 340 / | HD | COMMUNICATIONS: ELECTRICAL |
| 286.01 | DF | SYSTEMS {24} |
| 287 | DF | .~ Signal box type (e.g., to call messenger, plural fire alarm boxes) {11} |
| 297 | DF | .~.~ With signal at box (e.g., preliminary signal to combat false alarms) {3} |
| 299 | | .~.~.~ Simultaneous (e.g., actuated by transmitted signal) |