If the breaker is to be stored, it should be kept in a warm dry
location, protected from water, oil, dirt, or other damage. The
arc chambers must be kept covered to prevent foreign particles
lodging between the ceramic arc plates. If the arc chambers
have been stored under humid conditions, they must be dried
by baking for 24 hours at 60°C. before being placed in service.
Description and Installation
Description and Operating Principles
For the following principles of operation, refer to Fig. 1 on page
1.
Assume normal load current enters the upper stud and trav
els down through the pole and out through the lower stud.
Current flowing through the bucking-bar in the normal direc
tion sets up magnetic flux in the holding magnet in the direc
tion indicated in the figure. The holding coil, which is ener
gized by a separate direct current source, also sets up mag
netic flux in the opposite direction. The holding coil flux is suf
ficient to hold the breaker closed.
The main terminals may be connected to opposite polarities
to that shown. If they are, the holding coil connections also
should be reversed.
Whenever the current through the breaker increases rapidly,
the bucking-bar current increases to set up a flux through the
ARC Plates
Cross Magnetic
Field
Front ARC Horn
Rear ARC Horn
Fig.
2.
Schematic of Current Interruption
2
holding magnet and armature which is opposite to the flux set
up by the holding coil. As the bucking-bar current rises, the
resultant flux through the armature will be reduced to a value
that permits the armature to be pulled away by the spring load
on the linkage, and the breaker will open.
As the breaker starts to open, the main contacts part first and
cause the current to flow through the arcing contacts as shown
on Fig. 2. The arcing contacts then part and an arc forms be
tween them. The arc increases in length and rises until it im
pinges on the arc horns. The current then must flow through
the coils of the blow-out magnet. Thus a strong magnetic field
is produced between the side magnets on either side of the arc
chamber. The arc, travelling through this strong magnetic field,
is then forced upward into the slot of the ceramic plates of the
arc chamber and is extinguished.
The general construction of the breaker is indicated in Fig. 3,
which shows the moving contact arm in the position where
the arcing contact tips are just touching. The closing linkage is
comprised of three links which form two toggle systems. The
first toggle is comprised of pin B, Fig. 3, and the links on either
side. Although pin B does not go over center, the toggle can
not collapse as long as the armature, H, is held by the mag
netic attraction of the holding magnet. However, if the buck
ing-bar current increases, or if the holding coil current is inter
rupted, the armature will be released and pin B will move up
ward which causes its toggle to collapse and the moving con-
Fig.
3.
Schematic of Operating Mechanism
I.B. 201
www
. ElectricalPartManuals
. com
