User`s guide

Volume 3—Power Distribution and Control Assemblies CA08100004E—November 2013 www.eaton.com V3-T9-269
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9.5
Metering Devices, Protective Relays, Software and Connectivity
Connectivity Options
General Wiring Guidelines—RS-485 Network
When communicating over
RS-485 networks to Eaton
products, the following
General Wiring Guidelines
should be used.
Rule 1: Cable Selection—
Twisted Shielded Pair (TSP)
Note: Cables specifically
designed for RS-485 applications
are highly recommended.
The RS-485 bus is a length of
Twisted Shielded Pair (TSP)
that includes a third
conductor (used for the
common wire), a braided
shield accompanied by a drain
wire, and nominal impedance
of 120 ohms.
●
Belden Wire and Cable
Company Part Number
3106A or equivalent
Rule 2: Cable Intermixing
Any cable in the Belden
3106A family can be
intermixed with each other
in the Modbus network.
Rule 3: System Topology,
Size and Capacity
●
Strict daisy chain must be
adhered to. A strict daisy
chain configuration is one
where the transmission
line connects from one
RS-485 receiver to the
next. The transmission line
appears as one continuous
line to the RS-485 driver
●
Maximum 32 devices
●
Line termination:
Maximum cable lengths of
4000 feet (1219m); longer
bus lengths will slow the
data rate
Rule 4: Cable Splicing
The prime goal is to create a
secure electrical connection
while minimizing exposure to
electrical transients. Ferrules
are used to dress cable ends.
Most devices have built-in
terminal blocks that can be
used for splicing. Additionally,
terminal blocks should be
utilized when splicing
elsewhere in the gear or
facility to ensure a secure
electrical connection.
Rule 5: Cable Shielding
The cable shielding and outer
jacket should not be stripped
back beyond 1-1/2 inches.
Three-pole terminal blocks
are used to ensure a
continuous metallic shield
ground path. To ensure a
secure electrical connection
when daisy chaining devices
that have built-in two-pole
terminal blocks, mechanically
crimp sleeves onto the two
shield path drain wires.
Rule 6: Cable Grounding
Ground the communication
network at only one point in
the network, preferably by
terminating the drain wire
to ground at the EOL node
(same location as the EOLR).
A solid earth ground is
accomplished by connecting
the shield ground path’s drain
wire to a #14 AWG or larger
multi-stranded wire that has
an impedance path of 1 ohm
or less to a known earth
ground.
Note: The building electrical
ground may not be effective since
it may travel through many
connections and considerable
distances before reaching earth
ground. In such cases, a new
ground path will be required since
the effectiveness of this shield
earth ground connection will
affect the integrity of data
transferred over the cable.
Rule 7: Cable Termination
End of Line Resistors (EOLR)
are necessary to maintain
signal strength and minimize
reflections. EOLR must
match the impedance of the
TSP. Two EOLR are needed
and should be located at both
ends of the RS-485 bus. If
there is only one device
connected to the Modbus
master, it is considered the
last device in the network and
should be terminated with a
120 ohm 1/4 watt terminating
resistor.
Rule 8: Device Addressing
●
Each device must have a
unique slave address
●
No two devices on the
same RS-485 network can
have the same slave
address
Ethernet Cable Specifications
For complete specifications,
refer to the IEEE 802.3
Ethernet specification.
RS-485 Wiring Guide—Three Terminal Devices
Notes
1
Transceiver (XCVR) Common Connected to:
I = Isolated
NI = Non Isolated
E = Earth Ground
2
Center terminal on InsulGard (marked with Ground symbol) is for shield splicing only and is electrically floating.
Device Name
A
(– Wire)
B
(+ Wire)
Common
Wire
XCVR
Common
1
Data
Bias
IQ 230M 12 (MOD2) 11 (MOD1) 10 (INCOM 3) I 26V None
IQ 250 (–)
Older Models are Marked
B (–)
(+)
Older Models are Marked
A (–) or A(+)
SH I None
IQ 260 (–)
Older Models are Marked
B (–)
(+)
Older Models are Marked
A (–) or A (+)
SH I None
IQ 330M 12 (MOD2) 11 (MOD1) 10 (INCOM 3) I 26V None
NETLINK 1 (DATA–) 2 (DATA+) 5 (GND) E None
InsulGard
2
B A None Floating None
Bushing Gard
2
(InsulGard G3
2
)
B A None Floating None
Power Xpert Meter
4000/6000/8000
Data A
750B-S
Data B
750B-S
Shield
(COM)
I 300V 750 Ohm
Switch Sel
Power Xpert Gateway
400//600
A(–) B(+) COM I —