ABB S800 I/O User Manual page 91

In a "duplex connection" a cable break or loss of a TB820 will only affect the
clusters down-stream of the break. In a "simplex connection" a cable break or loss
of a TB820 will affect all I/O expansion clusters on the ModuleBus.
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The TB820 requires 24V d.c. (19.2 - 30V) with a maximum current requirement of
1,4 Ampere. The TB820 can be powered by either a single or redundant power
supply. If a redundant power supply is used, the TB820 can monitor the status of
each supply and send the status back to the FCI of the I/O Station. See
for power supply connections.
From Power Supply
The incoming power can then be distributed to other TB820s or the I/O modules if
desired. Refer to
diagrams.
If the distributed power needs to be independent of whether the power plugs are
removed or not, then the L+ and L- terminals should be bridged
3BSE 020 923R101
TB820
SA
L+ L+
L- L-
X1B
X1A
Power Supply "B"
Monitor
Power Supply "A"
Monitor
+24V d.c.
0V d.c.
Avtˆ…r "( U7'!ÃQ‚r…ÃTˆƒƒy’Ã8‚rp‡v‚†
Figure 3-11
Brr…hyÃDs‚…€h‡v‚ÃhqÃD†‡hyyh‡v‚ÃV†r…¶†ÃBˆvqr
Trp‡v‚Ã" 
SB
X5
X4
Rx Rx
Tx Tx
Jumper
and Figure 3-12 for power supply connection
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Figure 3-9
Terminal
Headers
+24V d.c.
To MTUs
(I/O Modules)
0V d.c.
81