The device is designed and tested for electrical safety in accordance with EN 60950-1.
It is connected to the peripheral devices (power supply, any local reading pulse sen‐
sor(s), PLC) via shielded cables. The cable shield – for the data cable, for example –
rests against the metal housing of the device. The device can either be grounded
through the cable shield or through one of the threaded mounting holes.
If the peripheral devices have metal housings and if the cable shields also lie on their
housings, it is assumed that all devices involved in the installation have the
same
ground potential
.
This is achieved by complying with the following conditions:
■
Mounting the devices on conductive metal surfaces
■
Correct grounding of the devices/metal surfaces in the system.
■
If necessary: low-impedance and current-carrying equipotential bonding between
areas with different ground potentials
SICK
device
closed current loop with equalizing
currents via cable shield
grounding point 2
grounding point 1
grounding potential difference
e. g. PLC
e. g. sensor
I
U
= metal housing
= shielded electrical cable
Figure 22: Occurrence of equipotential bonding currents in the system configuration
If these conditions are not fulfilled, equipotential bonding currents can flow along the
cable shielding between the devices due to differing ground potentials; this can be dan‐
gerous. This is, for example, possible in cases where there are devices within a widely
distributed system covering several buildings.
Remedial measures
The most common solution to prevent equipotential bonding currents on cable shields
is to ensure low-impedance and current-carrying equipotential bonding. If this is not
possible, the following solution approaches serve as a suggestion.
NOTICE
We expressly advise against opening up the cable shields. This would mean that the
EMC limit values can no longer be complied with and that the safe operation of the
device data interfaces can no longer be guaranteed.
Measures for widely distributed system installations
On widely distributed system installations with correspondingly large potential differen‐
ces, the setting up of local islands and connecting them using commercially available
electro-optical signal isolators
is recommended. This measure achieves a high degree
of resistance to electromagnetic interference while at the same time complying with all
the requirements of EN 60950-1.
6
ELECTRICAL INSTALLATION
34
O P E R A T I N G I N S T R U C T I O N S | CLV63x, CLV64x, CLV65x
8019588/2017-01-20 | SICK
Subject to change without notice