Installation and Connection
page 55
NF 650 - rev. 01 / 29.06.2020
sensors to a low level in a supply-side overvoltage event.
Observe the connection direction
Observe the non-reversed connection (p-side to transmitter) as well as a correct, straight
wiring supply. Ground (earth) must lead to the unprotected side.
The overvoltage protection devices are ineffective if wired incorrectly.
The following figure shows an example of an installation powered by the AC mains with
overvoltage protectors “EnerPro” (to the mains) and “SonicPro T” (to the transit time sensors).
The “EnerPro” overvoltage protector may also be installed inside the control cabinet, but the
separate earth connector “G” must be retained. The combination with “P” or “C” is very risky
in the event of overvoltage. NIVUS recommends that the earth connectors are separated to
guard against overvoltages.
P Earth connection for the “SonicPro T” overvoltage protectors on the sensor side
C Ground connection for transmitter installation
G Ground connection for AC mains overvoltage protection
1) Low impulse earthing resistance required
Do not reverse protected (p) and unprotected sides of overvoltage protection
Fig. 24-6
Typical installation with “SonicPro T” overvoltage protection
Three different earthing connections are shown in the drawing:
• P, C and G
It is important that all three earth terminals in the installation, in particular the earth terminal
“G”, have a
low surge earth resistance
, as high surge leakage currents may flow.
If the impact earthing resistance of a bad earth electrode is 1 Ω, a leakage current of 5 kA will
cause a peak voltage of 5000 V.
If this leakage current is routed to the control cabinet earthing via the DIN rail contact of an
overvoltage element, for example, the potential of the transmitter earthing increases and a
compensating current can flow through the sensor cables. There is a risk that the sensor lines,
the cables or the transmitter could be destroyed.
A deep earthing system can be used, for example, to achieve low resistance earthing. If this
cannot be realized at the installation site, the mutual interaction of different earth electrodes
should be reduced by routing the leakage currents to different independent earth electrodes.
Here, the leakage currents should be routed through conductors as widely separated as possi-
ble from one another.
If it can be assumed in applications that no overvoltages can be induced from the sensor
side, there will be no leakage currents through the earth connection “P”. This can then be tied
directly to the transmitter grounding “C”.
