Cable Length Calculations For 1728 And 1736; Technical Manual Ft1020G3 Rev - Panasonic Firetracker FT1020G3 CIE Technical And Programming Manual

current calculation spread sheet to calculate the expected total current
consumption
26.2

Cable Length Calculations for 1728 and 1736

Up to 16 display units type 1728 and/or 1736 can be connected depending on the cable
(type and length) being used.
Brooks recommendation:
Cable type Brooks BAC0898 1.5 mm
However other twisted pair cables with minimum 0.5 mm
category 5 (CAT5) cables, normal CAT5 cable resistance is 188Ω/Km. RS485 cable length
must not exceed 1200 metres.
In order to reduce noise immunity due to noisy environment, it is recommended to use
CAT5 with shield and terminate the shield in the CIE
Note: End of line resistor on the last unit is 120 Ω, this must be set in the last unit using
jumper link in the unit, refer to the Technical Manual for 1728 and 1736.
For ease of calculation, it is recommended to use 2 pairs of Brooks BAC0898 twisted pair
cable for 24V supply and RS485.
See
Table 15, this should be the benchmark against other alternative cables if other cables are
used.
Wire resistance for this cable (R
The current consumption of these units are given in
Table 15 page 173. Typically, calculations are based on their "Active State". For the
External Presentation Unit 1728 to continue working under worst case scenario, i.e. mains
failure and system is relying only on the back-up battery. The battery voltage should not
drop below 12V
Here is an example to calculate the cable distance from the CIE to the last 1728 unit under
these conditions (assuming that only 1728 units are connected and Brooks cable BAC0898
is used):
Current consumption of each 1728, I
Voltage of 1728 in "Active State", V
Number of units required
Nominal battery voltage, V
Maximum allowable battery voltage drop, V
Total current consumption for 16 units, I
Allowed cable resistance, R
R , for BAC0898 1.5mm
u
resistance was given as
The maximum cable length for 16 units, L
before using this graph in Figure 56.
2
), is approx. 11.9 Ω / Km at 20C.
u
and should still be able to deliver the active current consumption (88mA).
DC
unit
act
batt
allowed
2
twisted pair wire
172
Technical/Programming Manual
twisted pair for the 24V supply and for RS485.
2
can be used for RS485 e.g.
=
=
=
=
=
drop
=
=
=
total
=
=
=
=
=
= R
allowed
=
=
FT1020G3 Rev 2.2.1
0.088 A
12 V
16
24 V
V - V
batt act
24-12 V
12 V
16x0.088 A
1.408 A
Ω
V /I
drop total
12/1.408 Ω
8.52 Ω
11.9 Ω/Km
(Ω) / R (Ω/Km) Km
u
8.52/11.9 Km
0.716 Km