Crowcon Crowcon Gasmaster, Инструкция по установке, эксплуатации и обслуживанию, Страница: 10 / 48

Installation Crowcon Gasmaster
6
 Fire detectors,
Crowcon recommends the use of twisted-pair
cable, screened with an overall protective
sheath that is fireproof, for example, Pirelli
FP200 or similar. A 1K8 end-of-line resistor
must be fitted to the last detector on each
conventional smoke or heat detector loop.
Alternative cabling techniques, such as steel con-
duit, may be acceptable provided that appropriate
standards are met.
The minimum acceptable supply voltage meas-
ured at the detector and the maximum current
drawn by that detector is different for each
device. Please refer to the relevant Installation,
Operating and Maintenance Instructions provided
with each detector to calculate the maximum
cable distances allowed for different cable types.
The maximum cable distance allowed is depend-
ent upon the installation, for example, whether
Zener Barriers or Galvanic Isolators are required
(for I.S. devices) or not.
When calculating maximum cable distances for
detectors, assume a minimum supply of 19 V and
a sense resistance of 98
Ω (
39
Ω
for convential
fire channels).
Table 1: Typical cable characteristics
c.s.a
(mm2)*
Resistance (
Ω
per km)
Cable Loop
0.5 (20) 39.0 78.0
1.0 (17) 18.1 36.2
1.5 (15) 12.1 24.2
2.5 (13) 8.0 16.0
*Approximate c.s.a. in awg given in brackets.
Cable lengths should be calculated according to
the equations defined in the detector instructions
sheet and the cable and Gasmaster characteristics
specified above.
There are a number of suitable ways of terminat-
ing cables and glands to Gasmaster dependant on
the cable and gland type:
– Steel wire-armoured (SWA) cable and glands
with electrical termination of the armour to
the enclosure via the gland.
– Screened cable with the screen terminated
inside the enclosure via a metal tag attached
to the gland.
– Screened cable using an EMC gland where
the screen is terminated to the enclosure via
the gland.
– For detectors, 4-20 mA outputs and RS-485
terminations: screened cable where the
screen is connected to the SCR terminal on
the appropriate terminal strip.
2.5 Installing gas and fire
detectors
Install gas and fire detectors as per instrument
installation manuals, paying attention to location
and cabling requirements. For ESU devices please
refer to installation manual provided.
2.6 Installing output devices
Gasmaster can drive 12 V dc or 24 V dc audi-
ble visual alarms directly via the Audible Visual
drive terminals on the terminal PCB. Relays are
provided for switching additional outputs, and
12 V dc or 24 V dc 200 mA auxiliary supplies are
available adjacent to each block of relay terminals
for switching low power devices. Section 2.9
provides detailed information on connections to
output devices.
2.7 Connecting mains power
Connect the external power supply using the two
part screw terminals, refer to Figures 2.4 and 2.5.
Gasmaster must be earthed either at the power
connector earth terminal (see Figure 2.4) or using
the stud on top of the enclosure.
Figure 2.4
+
+
+
+ +
+
Pb
CROWCON
Mains connection terminals on terminal PCB