Both the tower and vault control panels are wired
into a double-throw transfer-relay cabinet located in
the vault. That is shown in figure 6-34 with a single line
representing the control cable. The transfer relay can
connect either control panel to the pilot-relay cabinet.
It can switch the system control from the tower to the
vault or from the vault to the tower. The transfer relay
has an eight-pole, double-throw, transfer-relay
assembly unit. This unit is actuated by a toggleswitch.
The low-burden pilot relay is designed to operate
at a wide range of voltages lower than the designed
l20-volt ac rating. The pilot relay can be actuated at
voltages from 50 to 90 volts ac.
The standard control cable is a No. 7 conductor,
600-volt, insulated, polychloroprene-sheathed cable.
One conductor (black) is a No. 12 American Wire
Gauge (AWG), and the remaining conductors are No.
16 AWG. The No. 12 conductor is the hot lead, and the
No. 16, the switch legs.
Several different lighting circuits are used on air-
fields: runway edge lighting circuits, taxiway lighting
circuits, approach lighting circuits, obstruction ligh-
ting circuits, beacon lighting circuits, and the
Figure 6-34.Airfield lighting control system