Rockwell Automation T80004 Application Note Field Loop Configuration - Manual (Page 34)

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AN-T80004 Field Loop Configuration
Issue 10 Jun 13 AN-T80004 34
‘Standard’ cables have two short tails on the chassis end. These cables are TC-205, 207, 505 or 507.
One tail connects to the field power supply via a T8290 or T8297 distribution unit. The other connects
to the power supply zero volts to provide a reference to the module for measuring the supply voltage,
through a plug which fits onto a T8290. The power return is still connected to the FTA, but the FTA has
no supply connection (so there is no point in wiring the five supply terminals on terminal block PWR TB
to the field supply).
Power Termination
The T8290 is appropriate for digital outputs, because it provides simple termination of the field supply
and zero volt reference. The T8297 does not have termination for the zero volt reference; instead it has
diodes for bridging low current power supplies. It is therefore appropriate for analogue outputs or for
very low power digital outputs.
It is recommended to supply the Trusted system and field circuits with fully separated dual supplies.
This ensures that a fault in one supply (e.g. a busbar short) will not cause a fault in the other supply
and bring the system down or cause shutdowns. Application note AN-T80005 demonstrates how to
design the power supplies. Bridging diodes are fitted in all modules wherever the dual supplies are
joined, except for digital output power. Therefore the dual supplies for digital outputs should be passed
through high current diodes mounted on suitably rated heatsinks before connection to the T8290 or
T8297 studs, which simply link the two supplies together.
The T8290 is rated at 60A. The T8297 studs are also rated at 60A and connect directly to the power
sockets in the same way as the T8290. A T8297 may be used for combining digital output power, given
that the zero volt reference connections are taken to the power supply by other means. The T8297 also
has a central terminal block for connecting field power, which is wired through bridging diodes. This is
ideal for analogue outputs, but the diodes are not adequate for digital outputs.
I/O cable TC-219 provides free wire terminations (instead of plugs) for supply power and zero volt
reference when using T8850 or T8870 FTAs. There is no TC-519. This allows custom terminations for
power supplies instead of T8290 or T8297.
Refer to application note AN-T80008 for information on protecting individual supply connections.
T8472 Termination
The T8472 is terminated using the T8871 FTA and special cables TC-221 and TC-521. The
terminations are described in the product descriptions for these parts. AC power (L,N,E) is connected
at the FTA on two separate terminal blocks for the two power groups and is fed back through the cable
to the module. TC-521 requires a special hot-swap jumper cable TC-310-02.
Output
module
Field Supply
Load
FTA