Specifications

24
Schneider Electric
Implementation guidelines
Sensitivity of various types of cable
Note: Shielded cables are not sensitive and do not generate interference.
Implementation of shielded cable
Where should the shielding be connected?
b Connect both ends of the external shielding of all digital or power cables to ground
at equipment entries.
b Only low-level, low frequency analogue links may in some cases require grounding
at one end only.
Unlike one-end connections, two-end connections allow low-frequency currents to
flow on the shielding (voltage between the two ends or ground loop). This current
generates a low voltage or 50 Hz noise on the pair inside.
Type Cable Type of signal EMC behavior
1 Analogue Power supply and
measurement circuits
for analogue sensors
Sensitive signals
2 Digital and
telecommunications
Digital circuits and data
buses
These signals are
sensitive. They also
interfere with family 1
3 Relay Dry contact circuits
with risk of flashover
These signals interfere
with families 1 and 2
4 Power supply Power supply and
power circuits
These signals
generate interference
b The manufacturer’s instructions should
always be followed when installing devices.
b Cabling configuration must always be
adapted to fit the topology of the system.
This configuration differs depending on
whether the network is a star, ring or bus.
In any case, the following are general
guidelines and can be applied whatever the
topology or type of signal carried.
b One-end connection of shielding protects
against low frequency currents.
b Two-end connection of shielding protects
against the most severe interference, i.e.
high frequency common mode.
Thus when the connection is at one end
only, the differential signals are protected at
low frequency, but at high frequency this
type of connection is ineffective.
Cabling Guidelines