Ft1020G3 Cable Length Calculation; Com Loop Cable Length - Panasonic Firetracker FT1020G3 CIE Technical And Programming Manual

26

FT1020G3 cable length calculation

26.1

COM loop Cable length

On each COM loop, up to 255 COM loop units can be connected (i.e. address 1-
255).
The cable length and maximum COM loop current are dependent on the number and
type of loop units and cable type, see Figure 56 page 171. Brooks recommends 1.50mm
twisted pair cable or equivalent for the COM loops. Brooks BAC0898 is available in the
following size cable reels.
The cable specifications for these 1.5mm

DC Cable Resistance: 11.9 Ω/Km per conductor at 20C.

Cable capacitance: 50pF/m at 1MHz.
Generally, the maximum allowed loop current is 350mA while the maximum allowable
loop resistance is 42.3Ω.
This maximum loop current should be taken into account when calculating the maximum
loop cable length. Either use the graph in Figure 56 or use this equation that represents
the graph to calculate the cable length.
Calculations of the maximum allowable distance from the Control Unit to the furthest end
or the total COM loop distance are based on the above specifications. Note that these
calculations do not take into account device loading along the loop.
Excel sheet
An Excel sheet is also available for an easy check of the current consumption, cable length,
etc.
EBLWin
In the COM loop pop-up menu select "Properties..." to open a window showing the
quiescent and maximum current consumption for the units connected to that COM loop.
Example:
A fire alarm manufacturer (Panasonic) specifies a maximum allowable loop resistance of
42.3Ω. What is the maximum allowable distance from the Control Unit to the last device if
Brooks BAC0898 stranded, un-coated copper wire was used? How does this change if the
temperature is increased to 80C?
�� = 42.3 ٠= 2��
������
�� = �� �� Ω
�� ��
�� = 42.3 ٠= 2��
������
Given that
�� = 11.9 ٠1000��
��
�� = 20��
������
Reel Length (meters)
100
200
250
500
Ω
��
�� Ω
��
⁄
= 0.0119 Ω/��
Technical/Programming Manual
Brooks Part Number
BAC0898
BAC0898/200
BAC0898/250
BAC0898/500
2
twisted cables are:
170
FT1020G3 Rev 2.2.1
2
,
R
W
R
W
D=L/2