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 TM 55-1905-219-14-9
4-47. ALARM SWITCHBOARD-MAINTENANCE INSTRUCTIONS (Continued).
(c) Location of single or multiple grounds.
1
In order to locate a ground, throw the circuit test switch momentarily to the "Off" position. The switch
causing the ground lamp to go out has ground on either the positive or negative side of its line,
depending on which ground lamp was lighted.
2
If the lamp fails to go out, a multiple ground is in the circuit. Throw the circuit test switches to the
"OFF" position one after another, but do not return them to " ormal" immediately. If the ground
N
lamp darkens, the last circuit test switch operated has a ground on its line. Return the rest of the
circuit test switches to normal one by one. If the ground lamp glows brightly again, there is also a
ground on the line of that switch.
(3) Simultaneous Grounds.
(a) Determination of simultaneous grounds. Simultaneous grounds have no immediate ground lamp
indication, but instead, send in a false alarm. When an alarm is indicated, and on throwing the circuit test
switch to the " ff" position, the negative ground lamp is lighted and there is a simultaneous ground on the
O
circuit.
(b) Location of simultaneous grounds. The one ground is on the L2 side of the unit which sent in the
false alarm. The second ground can be located by throwing the remaining circuit test switches momentarily to
the " ff" position until the negative lamp, PL4, goes out. The circuit test switch which causes the lamp to go
O
out has ground on its L2 line.
(4) Switchboard Grounds. If the ground lamp still glows after testing for single or multiple grounds, the
ground must be in the internal wiring of the switchboard. Such grounds will have to be located by inspection
and corrected immediately.
(f)
Maintenance.
(1) The supervisory alarm system is designed so as to require very little routine maintenance. Almost
anything that can happen to the system will give a warning of some kind or another. Faults should be corrected
all soon as discovered.
(2) Two Line Units.
The two line units which are mounted on the alarm switchboard require no maintenance other than
replacements or adjustments shown to be necessary by routine tests.
4-1208
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