System information

CA08104001E For more information visit: www.eaton.com
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February 2009
Power Management Systems & Products
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Sheet 02
Network Connectivity
Wiring Guidelines
017
General Wiring Guidelines — RS-485 Network
Table 2.2-5. RS-485 Wiring Guide — Three Terminal Devices

Transceiver (XCVR) Common Connected to:
I = Isolated
NI = Non Isolated
E = Earth Ground

Center terminal on Insulgard (marked with Ground symbol) is for shield splicing only and is
electrically floating.
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 4,000 feet (1,219 m);
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 which 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.
Device Name A
(– Wire)
B
(+ Wire)
Common
Wire
XCVR
Common

Data
Bias
IQ230M 12 (MOD2) 11 (MOD1) 10 (INCOM 3) I 26V None
IQ250 (–)
Older Models
are Marked
B (-)
(+)
Older Models
are Marked
A (-) or A(+)
SH I None
IQ260 (–)
Older Models
are Marked
B (-)
(+)
Older Models
are Marked
A (-) or A (+)
SH I None
IQ330M 12 (MOD2) 11 (MOD1) 10 (INCOM 3) I 26V None
NETLINK 1 (DATA–) 2 (DATA+) 5 (GND) E None
InsulGard

B A None Floating None
Bushing Gard

(InsulGard G3

)
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 —
Rule 5: Cable Shielding
The cable shielding and outer jacket
should not be stripped back beyond
1-1/2 inches. 3-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 2-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, prefera-
bly 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.