Figure 9-13.--Ten-line alarm switchboard.
The equipment necessary for supervising a circuit
The B-51 alarm panel, or two-line alarm unit (fig. 9-
or contact maker is comprised of an alarm-target
14), provides complete equipment for supervising two
relay, a supervisory-target relay, and a three-position
circuits or contact-maker lines. Five of these alarm
rotary switch. Two sets of the equipment constitute a
units are mounted for each 10-line panel.
two-line alarm unit.
Each unit is secured to its case by four screws.
The two-line panel has two alarm relays mounted
This method of mounting permits the inspection of a
side by side at the rear and near the bottom of the unit
unit by simply removing the four screws and pulling
panel. Each relay has an indicator drum that projects
the unit out of its housing.