Rockwell Automation AADvance Controller System Build - Manual (Page 41)

Document: 553632
(ICSTT-RM448_EN_P) Issue: 08:
2-11
Design Considerations for Electrical Grounding Design Considerations for Electrical Grounding Design Considerations for Electrical Grounding Design Considerations for Electrical Grounding
All applications of the controller will require at least two separate ground (earth)
systems:
An AC safety ground (sometimes called the 'dirty ground') to protect people in the
event of a fault. The ground stud on the T9100 processor base unit, and all
exposed metalwork such as DIN rails, will be bonded to the AC safety ground.
An instrument ground (sometimes called the 'clean ground' or the '0V dc ground')
to provide a good stable 0V reference for the system. Every signal return will be
referenced to the instrument ground. The instrument ground will be isolated from
the AC safety ground.
The AC safety ground and the instrument ground will usually be made available
through busbars. Busbars shall be of copper; they may be nickel plated. For a small
application, you may use ground studs instead of busbars.
Some field wiring, such as communications cables, will need shielded (screened) cable.
There may be a shield ground, in addition to the AC safety and instrument grounds, to
provide a common point to terminate shields of such cables. The shield ground will
usually be connected to the AC safety ground; or, more rarely, to the instrument
ground. In practice, the continuity of the shield connections will be more important
than the goodness of the ground connection provided.
The controller input and output modules incorporate galvanic isolation. Nevertheless,
it is possible that a particular application will require the provision of barrier strips
with galvanic isolation, for example to provide consistency with an existing installation.
In these cases, there may be a separate intrinsic safety ground as well.
Power Supply Require Power Supply Require Power Supply Require Power Supply Requirements ments ments ments
A controller requires the following power supply sources:
A dual redundant power supply of + 24V dc with an operating range of 18V dc to
32V dc.
Note: An AADvance controller is designed to accept supply transient and
interference according to IEC 61131 part 2.n
An over current fault in the controller must not result in the whole system losing
power. Consequently, the power sources must be able to deliver the peak current
needed to open any over current protection devices (such as fuses) without
themselves failing.
The power supply protection of the controller is within the modules, the power
distribution arrangement must provide a circuit breaker on the input side of each
power source.
Note: A controller is designed to withstand a reverse polarity connection without
permanent damage.
The power sources should come from a commercially available industrial un-
interruptible power supply (UPS) system. A suitable UPS should have capacity sufficient
to meet the entire system load (including field devices as well as the controller) and a
suitable contingency allowance for any projected future expansion.