MB30-CS datasheet(8/105 Pages) MITSUBISHI

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3.2 Switching Mechanism

The ON, OFF and TRIPPED conditions are shown in

Fig. 3.2. In passing from ON to OFF, the handle ten-

sion spring passes through alignment with the toggle

link (“dead point” condition). In so doing, a positive,

rapid contact-opening action is produced; the OFF to

ON contact closing acts in a similar way (“quick make”

and “quick break” actions). In both cases the action of

the contacts is always rapid and positive, and inde-

pendent of the human element – i.e., the force or

speed of the handle.

In auto tripping a rotation of the bracket releases

the cradle and operates the toggle link to produce the

contact-opening action described above. In the tripped

condition the handle assumes the center position be-

tween on and off, providing a visual indication of the

tripped condition. Also, auto trip is “trip free,” so that

the handle cannot be used to hold the breaker in the

ON condition. The protective contact-opening func-

tion cannot be defeated.

In multipole breakers the poles are separated by

integral barriers in the molded case. The moving con-

tacts of the poles are attached to the central toggle

link by a common-trip bar, however, so that tripping,

opening and closing of all poles is always simulta-

neous. This is the “common trip” feature, by which

single phasing and similar unbalance malfunctions are

effectively prevented.

Spring tension line

Toggle link

Cradle

Bracket

Spring

a) On

b) Off

c) Tripped

ON to OFF dead-point line

OFF to ON dead-point line

Handle centered; indicates

tripped condition

Fig. 3.2 Switching Mechanism Action

3.3 Automatic Tripping Device

There are three types of device, the thermal-magnetic

type, the hydraulic-magnetic type and the electronic

trip relay type.

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