Brooks FireTracker FT2GAS, Operation And Technical Manual

Page: 38 / 58

FT2GAS
Gaseous Extinguishing System
Rev No. 1.3
38
Example:
If the manufacturer specified cable resistance of a two-core cable is 0.02 Ohms per metre, the real
resistance will be 0.04 Ohms per metre and the maximum zone cable length will be 50 / 0.04 = 1250
metres.
4.3.4 Output Cable
For each dry-contact output, the cable length shall be determined by the connected equipment or
devices and the total cumulated cable resistance should be less than 50 Ohms.
For each power output, the maximum cable length can be calculated by the following equation.
L
MAX
= (V
LOWEST
- V
WORKING
) / (R
RPM
x I
MAX
) (Equation 2)
While L
MAX
- the maximum cable length,
V
LOWEST
- the lowest power supply voltage,
V
WORKING
- the minimum working voltage of the output device,
I
MAX
- the maximum current,
R
RPM
- the real resistance per metre.
Example:
The lowest voltage of the system power supply is fixed at 22V. For example, the device minimum working
voltage is 18V, the maximum current is 0.5A and the real cable resistance is 0.04 Ohms per metre. The
calculated maximum cable length will be (22 - 18) / (0.04 x 0.5) = 200 metres.
4.3.5 Requirements and Reference Cable Types
The requirements and the reference cable types are listed in Table 21 below. All specified maximum
distances specified in Table 21 shall be adhered to or more superior than the ones listed shall be used.
Table 21 Cable Types for Different Connections
Connection Requirement Cable Specifications
Maximum Cable
Length
Zone circuits Use Equation 1
Two core, Red, 1mm 2 conductive area,
Specified Cable Resistance 0.02
Ohm/m,
Real Cable Resistance 0.04 Ohms / m
1250 metres
Dry-contact
output
Use Equation 1.
Shall also meet the
external equipment
requirement.
Two core, Red, 1mm 2 conductive area
Specified Cable Resistance 0.02
Ohm/m,
Real Cable Resistance 0.04 Ohms / m
The shorter distance of
either 1250 metres or the
length required by the
external equipment
Alarm Devices
Output (ACF) Use Equation 2
Two cores, Red, 1.5mm
2
conductive
area
Specified Cable Resistance 0. 0128
Ohm / m,
Real Cable Resistance 0. 0256 Ohm/m
156 metres with up to 1A
current and the lowest
voltage of 18V
System
Inoperative
output
Use Equation 2
Two core, Red, 1.5mm 2 conductive area
Specified Cable Resistance 0. 0128
Ohms / m,
Real Cable Resistance 0. 0256 Ohm/m
312 metres with up to 0.5A
current and the lowest
voltage of 18V