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Planning the Installation
Page 26
Table 6: Voltage drop along cable
Current
Drawn
Cable Length (Standard 7/0.2 alarm cable)
10m
20m
30m
40m
50m
60m
70m
80m
90m
100m
60mA
0.10V
0.19V
0.29V
0.38V
0.48V
0.58V
0.67V
0.77V
0.86V
0.96V
80mA
0.13V
0.26V
0.38V
0.51V
0.64V
0.79V
0.90V
1.02V
1.15V
1.28V
100mA
0.16V
0.32V
0.48V
0.64V
0.80V
0.96V
1.12V
1.28V
1.44V
1.60V
120mA
0.19V
0.38V
0.58V
0.79V
0.96V
1.15V
1.34V
1.54V
1.74V
1.92V
140mA
0.22V
0.45V
0.67V
0.90V
1.12V
1.34V
1.57V
1.79V
2.02V
2.24V
160mA
0.26V
0.51V
0.77V
1.02V
1.28V
1.54V
1.79V
2.05V
2.30V
2.56V
180mA
0.29V
0.58V
0.86V
1.15V
1.44V
1.73V
2.02V
2.30V
2.59V
2.88V
200mA
0.32V
0.64V
0.96V
1.28V
1.60V
1.92V
2.24V
2.56V
2.88V
3.20V
220mA
0.35V
0.70V
1.06V
1.41V
1.76V
2.11V
2.46V
2.82V
3.17V
3.52V
240mA
0.38V
0.79V
1.15V
1.54V
1.92V
2.30V
2.69V
3.07V
3.46V
3.84V
260mA
0.42V
0.83V
1.25V
1.66V
2.08V
2.50V
2.91V
3.33V
3.74V
4.16V
280mA
0.45V
0.90V
1.34V
1.79V
2.24V
2.69V
3.14V
3.58V
4.03V
4.48V
300mA
0.48V
0.96V
1.44V
1.92V
2.40V
2.88V
3.36V
3.84V
4.32V
4.80V
320mA
0.51V
1.02V
1.55V
2.05V
2.56V
3.07V
3.58V
4.10V
4.61V
5.12V
340mA
0.54V
1.09V
1.63V
2.18V
2.72V
3.26V
3.81V
4.35V
4.90V
5.44V
360mA
0.58V
1.15V
1.73V
2.30V
2.88V
3.46V
4.03V
4.61V
5.18V
5.76V
380mA
0.61V
1.22V
1.82V
2.43V
3.04V
3.65V
4.26V
4.86V
5.47V
6.08V
400mA
0.64V
1.28V
1.92V
2.56V
3.20V
3.84V
4.48V
5.12V
5.76V
6.40V
You can reduce voltage drop using either or both of these methods:
Double-up the supply connections (12V and 0V). This will halve the resistance on
each core and therefore halve the voltage drop.
Supply power to the detection devices from the control unit's Aux output using two
additional cores in the cable (that is, use 6-core cable). This reduces the current
drawn from the bus connections and is the preferred method of reducing voltage drop,
since detectors generally operate at lower voltages (9.5V).
If you cannot reduce voltage drop sufficiently along a bus, install one or more remote
power supplies, as described next.
Note that if detectors connect to expanders or other bus devices, the current along the bus
is the total of the current drawn by the bus devices and detectors.
Using remote power supplies
When voltage drop along a bus cable exceeds requirements, or the demand on the control
unit's power supply exceeds its capacity, you should install one or more EXP-PSU remote
power supplies. Figure 5 shows the recommended method of connecting a remote power
supply. It should be fitted close to the equipment it is powering.
Figure 5. Connecting a remote power supply
Device 1
0V
Bus
Device 2
Remote PSU
Device 4
Device 3
12V
B
A
0V
12V
A
B