Correctly Wiring Electrically Isolated CAN Networks
6.3 Heavy Industrial Environment (Double Twisted Pair Cable)
6.3.1 General Rules
The following general rules for the CAN wiring with single shielded double twisted pair cable
should be followed:
1
A cable type with a wave impedance of about 120 Ω ±10% with an adequate conductor cross-section
(≥ 0.22 mm²) has to be used. The voltage drop over the wire has to be considered.
2
For heavy industrial environment use a four-wire CAN cable.
Connect
•
•
•
two twisted wires to the data signals (CAN_H, CAN_L) and
the other two twisted wires to the reference potential (CAN_GND) and
the cable shield to functional earth (FE) at least at one point.
3
The reference potential CAN_GND has to be connected to the functional earth (FE) at exactly one
point.
4
A CAN bus line must not branch (exception: short cable stubs) and has to be terminated with the
characteristic impedance of the line (generally 120 Ω ±10%) at both ends (between the signals CAN_L
and CAN_H and not to CAN_GND).
5
Keep cable stubs as short as possible (l < 0.3 m).
6
Select a working combination of bit rate and cable length.
7
Keep away CAN cables from disturbing sources. If this can not be avoided, double shielded cables are
recommended.
Figure 6: CAN wiring for heavy industrial environment
CAN-USB/2
Hardware Manual • Doc. No.: C.2066.21 / Rev. 1.6
Page 19 of 28
CAN GND
CAN_L
CAN_H
CAN_GND
n.c.
n.c.
n.c.
n.c.
n.c.
n.c.
n.c.
n.c.
n.c.
n.c.
CAN_L
CAN_H
CAN_GND
Shield
CAN_GND
twisted
twisted
5
6
7
9
8
1
4
3
2
9
1
4
5
6
7
3
8
2
n.c.
n.c.
Single shielded
double twisted pair cable
(four-wire cable,
2x 2x 0.22mm²)
wire shield
Wire Layout
(Example)
Signal assignment of single shielded double twisted pair cable
with earth and termination
n.c. = not connected
DSUB9 connector
(female or male)
pin designation
connector case
DSUB9 connector
(female or male)
pin designation
CAN cable with connectors
connector case
earth (FE)
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