■
Mounting the devices on conductive metal surfaces
■
Correctly grounding the devices and metal surfaces in the system
■
If necessary: low-impedance and current-carrying equipotential bonding between
areas with different ground potentials
If these conditions are not fulfilled, equipotential bonding currents can flow along the
cable shielding between the devices due to differing ground potentials and cause the
hazards specified. 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 equipo‐
tential bonding 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.
The use of electro-optical signal isolators between the islands isolates the ground loop.
Within the islands, a stable equipotential bonding prevents equalizing currents on the
cable shields.
Measures for small system installations
For smaller installations with only slight potential differences, insulated mounting of the
device and peripheral devices may be an adequate solution.
Even in the event of large differences in the ground potential, ground loops are effec‐
tively prevented. As a result, equalizing currents can no longer flow via the cable shields
and metal housing.
NOTICE
The voltage supply for the device and the connected peripheral devices must also
guarantee the required level of insulation.
Under certain circumstances, a tangible potential can develop between the insulated
metal housings and the local ground potential.
6.3
Connection principle
6.3.1
Service mode connection schematic
This operating mode is recommended for initial commissioning of the device.
6
ELECTRICAL INSTALLATION
28
O P E R A T I N G I N S T R U C T I O N S | GLS611
8026021/1D2S/2022-09-01 | SICK
Subject to change without notice
