5 Installation and Commissioning
61
In the case of devices with an external pressure sensor, the cable shield on the sensor side
is conductively connected to the sensor housing (provided by the manufacturer) - see
paragraph 5.6.1 In this case, the device is galvanically connected to the piping (grounded)
via the cable shield of the external pressure sensor.
Note:
If you do not want to ground the device, the pressure supply to the pressure sensor (internal
or external) of the device must be electrically insulated with a suitable insulating connector.
However, it is always necessary to ensure that no electrostatic charge is generated on the
surface of the device.
5.5.2.4 Grounding of overvoltage protection
The condition perfect grounding must be respected and used for surge protection devices on
all three levels. For individual levels of SPD, min. cross-sections of live conductors and PE
conductors (see [33] ). For SPD type 3, a PE conductor with a min. cross-section 1 mm
2
(for
SPD type 2 a minimum cross-section of PE conductor 6 mm
2
is prescribed).
5.5.2.5 Using of shielded cables
The connection of the corrector with other devices must be made with shielded cables.
Recommended types of shielded cables and their cross-sections and maximum lengths are
given in sections 3 and 5.6 and in the accessory’s manual [41]. In general, the requirements
for cables with intrinsically safe signals complying with the standard [10] for use in potentially
explosive atmospheres must be complied with. Cables must have good shielding. Unused
conductors of multicore cables with intrinsically safe signals must be treated in accordance
with [10].
5.5.2.6 Preventing the formation of unwanted current loops
When connecting the device to other devices, there must be no closed conductive loops for
the flow of any balancing currents. The balancing currents are caused by the difference
between the potentials in remote parts of the installation. In conductive loops (mostly
grounded), interfering currents are induced from RF interfering fields, which weakens the
efficiency of cable shielding.
The cable shield must be connected only on one side, in our case on the side of the corrector
or electronic recorder (see Fig. 19).
For cables connected to the internal terminals of the converter/recorder passing through a
metal gland, the shield must be conductively connected to the metal part of the cable gland
(see Fig. 20), i.e. essentially connected to the converter box - see paragraph 5.6.1. The
shield at the other end of the cables must not be connected.
The connected shield of all cables inside the converter via cable glands is conductively
connected to the metal body of the pressure sensor. Grounding is realized on the gas
pipeline by means of a 6 mm impulse tube of the gas supply to the pressure sensor.
Note – External pressure range
If the device uses an external pressure sensor instead of an internal pressure sensor, the
sensor cable shield must be connected to the converter in the cable gland. The shield on the
sensor side is conductively connected to the sensor body (provided by the manufacturer) -
see paragraph 5.6.1.
5.5.2.7 Concurrence of cables
Requirements for the distance of metallic cabling of data and information lines and cabling of
power distribution (a combination of shielded and unshielded cables) are given in the set of
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