Can-Bus; Cabling Specifications - Electro-Voice P3000RL Owner's Manual

CAN-BUS

Baud Rate
500 kbit/s
250 kbit/s
125 kbit/s
62.5 kbit/s
20 kbit/s
10 kbit/s
CABLE SPECIFICATIONS
According to the ISO 11898-2 standard, CAN-bus data transfer cabling has to be carried out using
Twisted-Pair cables with or without shielding providing a characteristic impedance of 120Ω. Both ends
of a CAN-bus need to be terminated with 120Ω termination-plugs.
The maximum bus-length depends on the actual data transfer rate, the kind of data transfer cable
being used, as well as the total number of participants on the bus. The following table shows the most
essential coherencies for CAN-networks consisting of up 64 participants:
Cable for data Transmission
Bus Length
Resistance per
Unit Length
0 ... 40 m < 70 mΩ/m
40 ... 300 m < 60 mΩ/m
300 ... 600 m < 40 mΩ/m
600 ... 1000 m < 26 mΩ/m
*
With longer cables and many participants on the CAN-bus, termination resistors with higher impedance than the
Ω
specified 120 are recommended to reduce the ohmic load of the interface drivers and therefore the voltage drop
between the two cable ends.
The following table is meant for first assessment of necessary cable diameters for different bus lengths
and bus-participant numbers:
Bus Length
100 m
250 m
500 m
Additionally, the length of branch lines – for participants that are not directly connected to the CAN-bus
– is also of importance. For data transfer rates of up to 125kbit/s, the maximum length of a single stub
cable should not exceed 2m. For higher bit rates a maximum length of only 0.3m is still permissible.
The entire length of all branch lines should not exceed 30 m.
General Note:
As long as only short distances (up to 10m) are concerned, common RJ-45 patch cables with
100Ω characteristic impedance (AWG 24 / AWG 26) can be used for the cabling inside of a rack-
shelf system. The previously outlined guidelines for network cabling are mandatory as far as
the rack-shelve interconnection or fixed installations are involved.
The CAN-bus allows using different data rates, with the data
Bus Length
rate being indirectly proportional to the bus length. Small
100 m
networks allow baud rates up to 500kbit/s.
250 m For sizable dimensioned networks reducing the baud rate
(minimum 10kbit/s) is necessary.
500 m
The integration of repeaters is generally recommended
1000 m
when the bus-length exceeds 1,000m.
2500 m
5000 m
Cable Diameter
0.25 ... 0.34 mm²
AWG23, AWG22
0.34 ... 0.6 mm²
AWG22, AWG20
0.5 ... 0.6 mm²
AWG20
0.75 ... 0.8 mm²
AWG18
Number of Appliance on the CAN-Bus
32
0.25 mm² or AWG24
0.34 mm² or AWG22
0.75 mm² or AWG18
Termination
124 Ω
127 Ω
*
150 Ω ... 300 Ω
*
150 Ω ... 300 Ω
64
0.34 mm² or AWG22
0.5 mm² or AWG20
0.75 mm² or AWG18
14
max.
Data Transfer Rate
1000 kbit/s at 40 m
500 kbit/s at 100 m
100 kbit/s at 500 m
62.5 kbit/s at 1000 m
100
0.34 mm² or AWG22
0.5 mm² or AWG20
1.0 mm² or AWG17