VEGA VEGAFLEX 66 (-110…+400°C) Foundation Fieldbus - Manual (Page 19)

In systems with potential equalisation, connect the cable
screen directly to ground potential at the power supply unit, in
the connection box and at the sensor. The screen in the sensor
must be connected directly to the internal ground terminal. The
ground terminal outside on the housing must be connected to
the potential equalisation (low impedance).
In systems without potential equalisation, connect the cable
screen directly to ground potential at the power supply unit and
at the sensor. In the connection box or T-distributor, the screen
of the short stub to the sensor must not be connected to
ground potential or to another cable screen. The cable screens
to the power supply unit and to the next distributor must be
connected to each other and also connected to ground
potential via a ceramic capacitor (e.g. 1 nF, 1500 V). The low
frequency potential equalisation currents are thus suppressed,
but the protective effect against high frequency interference
signals remains.
The total capacitance of the cable and of all capacitors must
not exceed 10 nF in Ex applications.
Take note of the corresponding installation regulations for Ex
applications. In particular, make sure that no potential equal-
isation currents flow over the cable screen. In case of
grounding on both sides this can be achieved by the use of a
capacitor or a separate potential equalisation.
5.2 Connection steps - Instrument housing
Proceed as follows:
1 Unscrew the housing cover
2 If an indicating and adjustment module is installed, remove
it by turning it slightly to the left.
3 Loosen compression nut of the cable entry
4 Remove approx. 10 cm (4 in) of the cable mantle, strip
approx. 1 cm (0.4 in) insulation from the ends of the
individual wires
5 Insert the cable through the cable gland into the sensor
6 Lift the opening levers of the terminals with a screwdriver
(see following illustration)
Cable screening and
grounding
Select connec-
tion cable for Ex
applications
VEGAFLEX 66 • Foundation Fieldbus 19
5 Connecting to power supply
32765
-
EN
-080716