Figure 3-10 General Partial Cross-Sectional View (Shown
in Closed Position) (not specific to any family/frame)
3-3.1 PRIMARY MOVING CONTACTS
Depending upon the frame size, each primary moving
contact assembly is comprised of multiple individual
copper contact fingers connected to the load conductor
through flexible braided connectors (Figure 3-8). Two
flexible connectors are used to connect each finger to
the load conductor. The number of fingers used
depends upon the circuit breaker’s continuous and
short-circuit current ratings (Figures 3-8 and 3-9). On
some ratings fingers are removed and replaced with
spacers.
The single contact finger performs both the main and
arcing contact functions on different parts of the same
finger (Figure 3-7). A highly conductive alloy pad is part
of the contact finger and functions as the moving main
contact, and is called the “Heel.” The tip of the same
contact finger functions as the moving arcing contact,
and is called the “Toe.”
In addition to the contact finger information given above,
DSX (MDSX) utililize an inner and outer carriage design
to facilitate a fast opening blow open contact structure
(Figure 3-9a). The contact fingers mounted in the inner
contact carrier can move independently from both the
outer carrier and the opening mechanism in the breaker.
This independence is the core design feature of its fast
opening blow open contact structure.
Figure 3-8 Narrow Frame (8-finger) Moving Conductor
Assembly
“Heel”
(Main Contact)
“Toe”
(Arcing Contact)
“Toe”
(Arcing Contact)
“Heel”
(Main Contact)
Figure 3-9a MDSX Moving Contact Assembly
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