Specifications

Bases
402
31007715 6/2008
Protective Earth One of the key functions of a PDM, in addition to distributing sensor and actuator
power to the I/O modules, is the provision of protective earth to the island. PE is
essentially a return line across the bus for fault currents generated at a sensor or
actuator device in the control system.
A captive screw at the bottom of the STB XBA 2200 base secures a PE wire to the
island:
1 The PE contact
2 The PE captive screw
PE is brought to the island by an insulated ground conductor, usually a copper wire
that is tied to a single grounding point on the cabinet. The ground conductor is
secured by the PE captive screw.
The STB XBA 2200 base distributes PE to the island via a single contact located at
the bottom left side of the base (item 2 above). The PDM base distributes PE to its
right and left along the island bus.
The single contact on the bottom left of the base is one of the ways to discriminate
the STB XBA 2200 from other size 2 bases. The PDM base does not need the four
field power contacts on its bottom left side—the PDM takes field power from an
external power supply via two power connectors on the front of the module and
distributes that power downstream to the I/O modules it supports.
1
2
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