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5 Connecting to the bus system
VEGAPULS 68 • Foundation Fieldbus
36538-EN-170405
5 Connecting to the bus system
5.1 Preparing the connection
Always keep in mind the following safety instructions:
Warning:
Connect only in the complete absence of line voltage.
•
The electrical connection must only be carried out by trained
personnel authorised by the plant operator.
•
If overvoltage surges are expected, overvoltage arresters should
be installed.
The instrument requires a operating voltage of 9 … 32 V DC. Operat-
ing voltage and the digital bus signal are carried on the same two-wire
connection cable. Power is supplied via the H1 power supply.
Connection is carried out with screened cable according to Fieldbus
specication.
Use cable with round cross section for instruments with housing and
cablegland.Toensurethesealeectofthecablegland(IPprotection
rating),ndoutwhichcableouterdiameterthecableglandissuitable
for.
Useacableglandttingthecablediameter.
Make sure that the entire installation is carried out according to the
Fieldbusspecication.Inparticular,makesurethatthebusistermi-
nated with suitable terminating resistors.
Metric threads
In the case of instrument housings with metric thread, the cable
glands are screwed in at the factory. They are sealed with plastic
plugs as transport protection.
You have to remove these plugs before electrical connection.
NPT thread
In the case of instrument housings with self-sealing NPT threads, it is
not possible to have the cable entries screwed in at the factory. The
free openings for the cable glands are therefore covered with red dust
protection caps as transport protection.
Prior to setup you have to replace these protective caps with ap-
proved cable glands or close the openings with suitable blind plugs.
On plastic housings, the NPT cable gland or the Conduit steel tube
must be screwed into the threaded insert without grease.
Max. torque for all housings, see chapter "Technical data".
Make sure that the cable screen and grounding are carried out ac-
cordingtoFieldbusspecication.Werecommendtoconnectthe
cable screen to ground potential on both ends.
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
Safety instructions
Voltage supply
Connection cable
Cable glands
Cable screening and
grounding
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