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5 Connecting to power supply
VEGABAR 55 • Foundation Fieldbus - climate compensated
39443-EN-130321
5 Connecting to power supply
5.1 Preparing the connection
Always keep in mind the following safety instructions:
•
Connect only in the complete absence of line voltage
•
If overvoltage surges are expected, overvoltage arresters should
beinstalledaccordingtoFoundationFieldbusspecication
Tip:
We recommend VEGA overvoltage arrester B63-32.
Inhazardousareasyoumusttakenoteoftherespectiveregulations,
conformityandtypeapprovalcerticatesofthesensorsandpower
supply units.
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.
Usecablewithroundcross-section.Acableouterdiameterof
5…9mm(0.2…0.35in)ensuresthesealeectofthecablegland.
Ifyouareusingcablewithadierentdiameterorcross-section,
exchange the seal or use a suitable cable gland.
Make sure that the entire installation is carried out according to the
Fieldbusspecication.Inparticular,makesurethatthebusistermi-
nated with suitable terminating resistors.
On the instrument with cable entry ½ NPT and plastic housing there is
ametallic½"threadedinsertmouldedintotheplastichousing.
Caution:
No grease should be used when screwing the NPT cable gland or
steel tube into the threaded insert. Standard grease can contain
additives that corrode the connection between threaded insert and
housing.Thiswouldinuencethestabilityoftheconnectionandthe
tightness of the housing.
With 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
Safety instructions
Voltage supply
Connection cable
Cablegland½NPT
Cable screening and
grounding
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