| 340 / | HD | COMMUNICATIONS: ELECTRICAL |
|
| 286.01 | DF | SYSTEMS {24} |
| 287 |  | .~ Signal box type (e.g., to call messenger, plural fire alarm boxes) {11} |
| 288 | DF | .~.~> Combined (e.g., alarm circuit over power line) {2} |
| 291 | DF | .~.~> Repeaters (e.g., from central to plural fire houses or to siren) |
| 292 | DF | .~.~> Circuit maintenance (e.g., fault alarm, faulty circuit substitution) |
| 293 | DF | .~.~> Variable signal (e.g., police and fire, first and third alarm) {1} |
| 295 | DF | .~.~> Noninterfering (prevents break-in by another box during transmission) {1} |
| 297 | DF | .~.~> With signal at box (e.g., preliminary signal to combat false alarms) {3} |
| 301 | DF | .~.~> Portable box actuating key (e.g., key must be released by signal from central) {1} |
| 303 | DF | .~.~> Frangible element must be broken to send signal |
| 304 | DF | .~.~> False alarm combating (e.g., detention devices) |
| 305 | DF | .~.~> Local circuit to actuate box {1} |
| 307 | DF | .~.~> Transmitters {2} |