Drop Cable Limitations
(Original Document)
About us
Overview
A drop cable creates a signal reflection on the transmission line characteristic of the trunk cable. In order to limit reflections, drop cables should be as short as possible.
Maximum Drop Cable Length
Respect the values listed in the following table:
Transmission Rate
Lmax
ΣLmax
TAP Distance
ΣLGmax
1 Mbit/s
0.3 m (0.98 ft)
0.6 m (0.98 ft)
1.5 m (4.92 ft)
800 kbit/s
3 m (9.84 ft)
6 m (19.68 ft)
3.6 m (11.81 ft)
15 m (49.21 ft)
500 kbit/s
5 m (16.4 ft)
10 m (32.8 ft)
6 m (19.68 ft)
30 m (98.42 ft)
250 kbit/s
5 m (16.4 ft)
10 m (32.8 ft)
6 m (19.68 ft)
60 m (196.84 ft)
125 kbit/s
5 m (16.4 ft)
10 m (32.8 ft)
6 m (19.68 ft)
120 m (393.69 ft)
50 kbit/s
60 m (196.84 ft)
120 m (393.69 ft)
72 m (236.21 ft)
300 m (984.24 ft)
20 kbit/s
150 m (492.12 ft)
300 m (984.24 ft)
180 m (590.54 ft)
750 m (2460.62 ft)
10 kbit/s
300 m (984.24 ft)
600 m (1968.49 ft)
360 m (1181.09 ft)
1500 m (4921.24 ft)
Lmax is the maximum length of 1 drop cable.
ΣLmax is the maximum value of the sum of drop cables on the same TAP.
TAP distance is the minimum distance necessary between 2 TAPs, can be calculated for each TAP (must be greater than 60% of the largest of the 2 ΣLmax).
ΣLGmax is the maximum value of the sum of drop cables on the network.
Calculation Example
The figure below provides an example of a TAP distance calculation with 2 junction boxes and 6 devices:
The TAP distance in the above example is calculated as follows:
Step
Description
Result
1
Calculating the sum of lengths of drop cables for each tap junction.
5 m (16 ft) and 7 m (22 ft)
2
Keeping the longest length.
7 m (22 ft)
3
Calculating the minimum cable length between the 2 TAPs.
60% of 7 m (22 ft)
Respect the TAP distance even if a device is in between.