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LST700 SERIES INSTALLATION & MAINTENANCE MANUAL • Approved Document No. DFU7002012 Rev 4
LST700 SERIES FIRE ALARM PANEL
END OF LINE
RESISTOR
(6k8 Ohm)
POLARISED
SOUNDER
POLARISED
SOUNDER
+
+
+
–
+
POLARISED
SOUNDER
+
✗
DO NOT SPUR
(wiring not
monitored)
PANEL
SOUNDER
CIRCUIT
TERMINALS
Sounder circuit wiring
Four conventional sounder circuits are available on the fire alarm panel. These can accommodate up
to 40 polarised sounders (at 20mA) or 32 bells (at 25mA) per system. If a full complement of sounders
or bells are to be used, they should be split as equally as possible across all four sounder circuits.
Figure 5 : Typical sounder circuit wiring
All sounders must be polarised as unpolarised sounders will show a sounder fault.
A 6k8 end of line resistor (provided in the panel’s accessory pack) must be connected at the end
of each sounder circuit to allow the wiring to be monitored.
The wiring for each sounder circuit should be connected to the relevant 5mm connector block on
the Main Control PCB (see page 13 for detailed second fix connection information).
Optional three-wire detector / sounder circuit connection method
An optional three wire detector / sounder connection method is also available. This method is very
similar to the four wire method explained above and on the previous page except the detector and
sounder circuits share a common 0V return wire.
Figure 6 : Typical three-wire detector / sounder circuit wiring
The advantages of the three wire method are that it utilises standard system components, can
sometimes lead to cost savings on installation (depending on the layout of the building) and is an
easy retrofit solution for many older mains based systems.
Disadvantages include its failure to meet the current standards since any fault on the common
wire affects both circuits. We strongly advise therefore that this method is only used with the
approval of the fire officer concerned.
Some cautionary points about the three wire method:-
■
Installers must ensure that an open or short circuit condition does not affect more than 40 devices in
TOTAL. This includes detectors, manual call points and sounders.
■
The common negative wire should be connected to the panel’s sounder circuit negative. It should
also be of low impedance as it carries all the current for the sounders and detectors.
■
If the sounders draw a lot of current or the wiring runs are long and have excessive resistance, the
voltage on the negative wiring may rise and cause the detectors to reset. This must be checked. We
cannot give exact figures as it varies from detector to detector.
SMOKE
OR HEAT
DETECTOR
MANUAL
CALL
POINT
MANUAL
CALL
POINT
SMOKE
OR HEAT
DETECTOR
END OF LINE
CAPACITOR
+
END OF LINE
RESISTOR
(6k8 Ohm)
POLARISED
SOUNDER
POLARISED
SOUNDER
+
+
+
+
–
–
POLARISED
SOUNDER
PANEL
DETECTOR
CIRCUIT
TERMINALS
PANEL
SOUNDER
CIRCUIT
TERMINALS
