Electrical installation
64 © SICK AG · Germany · All rights reserved · Subject to change without notice 8013796/ZM63/2017-05-09
Operating Instructions
LMS5xx Laser Measurement Sensors
Chapter 6
If these conditions are not met, e.g. on devices in a widely distributed system over several
buildings, potential equalization currents may, due to different ground potentials, flow along
the cable shields between the devices.
Fig. 40: Currents in the cable shields due to differences in ground potential
Due to insufficient ground potential equalization, voltage differences arise between the
grounding points 1 and 2. The current loop closes via the shielded cables and the housings.
Risk of injury/risk of damage via electrical current!
Potential equalization currents between the LMS5xx and the peripheral devices can have
the following effects:
Dangerous voltages on the metal housing, e.g of the LMS5xx
Incorrect function or irreparable damage to the devices
Damage/irreparable damage of the cable shield due to heating and cable fires
Where local conditions are unfavorable and thus do not meet conditions for a safe
earthing method (same ground potential at all grounding points), take measures from
the following explanations.
Remedial measures
The most common solution to prevent potential equalization currents on cable shields is to
ensure low-impedance and stable current carrying equipotential bonding. If this is not pos-
sible the following two solution approaches serve as a suggestion.
Important It is not advisable to open up the cable shields. This would mean that the EMC limit values
can no longer be complied with and the safe operation of the device data interfaces can no
longer be guaranteed.
Power
supply
PLC LMS5xx
Grounding point 1 Grounding point 2
U
Grounding potential difference
= Shielded electrical cable
= Metal housing
Closed current loop with equalizing
currents via cable shield
I
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