TYPE 4208 “J”
EARTH DETECTION MODULE
INTRODUCTION
The “J” module is designed to detect if -24VDC
The “J” module can either be mounted on its own
becomes grounded in the 4208 Fire Alarm System.
panel or on available space in other panels.
CIRCUIT OPERATION (FIG. 13)
EARTH DETECTION CIRCUIT
Normal Operation
Terminal 2i is connected to the building ground
(e.g. cold water pipe). Transistors Ql and Q2 are
biased “off” by a positive potential applied to the
base of the transistors from terminal 22 (+BAT.).
Negative Grounded Condition
When -24VDC becomes grounded, a negative po-
tential is applied to the base of transistor Ql which
causes Ql to conduct.
When Ql conducts, a negative potential is ap-
plied to the base of transistor Q2 which causes Q2
to conduct.
The conduction of Q2 completes the circuit
from terminai 27 (-24VDC) through relay Kl and
transistor Q2 to terminal 22 (+BAT.) which ener-
gizes relay IS1 .
When relay Kl energizes, its Kl A contacts trans-
fer which causes the EARTH lamp to illuminate
and causes a “trouble” condition in the “A” or
“AX” panel. Current flows from terminal 27 (-24
VDC) through contacts KlA (9&S), to terminal 25
where the current flow splits into two paths.
One path is from terminal 25 through the
EARTH lamp (illuminating the lamp) to terminal
22 (+BAT).
The other path is from terminal 25, through
diode D5, terminal 24 to terminal 5 on the “A” or
“AX” panel. The presence of -24VDC on terminal
5 causes a “Trouble” condition in the “A” or
“AX” panel. (Refer to “A” or “AX” panel - Trou-
ble Condition for detailed circuit description.)
27
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