Circuit breaker with transparent tube magnetic core holder

In a circuit breaker comprising switch contacts connected to terminals and connectable into a protected circuit and a winding in circuit between a terminal and a contact, including a switch handle, which enables at least the closing of the switch contacts and a mechanism for opening the contacts on overload including,

• a non-magnetic tube within the winding containing a solid core of magnetic material movable within the tube in a viscous liquid, the core being biased away from a pole piece at one end of the tube, the tube being oriented relative to the winding so that the core is urged by the magnetic field of the winding toward the pole when subject to overload current and
• a movable armature forming part of the mechanism, movement of which armature will open the closed contacts, whereby upon sustained overload the core moves toward the pole piece and when positioned sufficiently close to the pole piece will exert sufficient magnetic force on the armature to open the switch contacts,
• the improvement comprising making at least the tube side walls of material through which the level of the viscous liquid in the tube may be visibly checked.