Pole for a low-voltage limiting electrical power circuit breaker and a circuit breaker equipped with such a pole

A pole for a low-voltage limiting electrical power circuit breaker comprising an opening mechanism, the pole comprising:

• a frame;
• a first contact means comprising a contact area;
• a second contact means comprising:
• a movable support designed to be linked to the opening mechanism and movable with respect to the frame between a closed position and an open position,
• at least one contact finger movable parallel to a longitudinal mid-plane of the pole and able to take, with respect to the movable support in the closed position, a contact position in which the contact finger is in contact with the contact area of the first contact means, and a separated position in which the contact finger is separated from the first contact means, and
• a flexible return means designed to return the movable contact finger to its contact position, when the movable contact finger is close to its contact position;
• an arc extinguishing chamber, comprising an outlet opening constituting the exhaust channel for outlet of all the gases emitted when breaking is performed, an inlet opening situated between the contact area and the outlet opening, arc energy absorption means situated inside the arc extinguishing chamber, and side walls laterally confining the arc extinguishing chamber, the distance measured perpendicularly to the longitudinal mid-plane between the side walls defining a width of the chamber;
• a magnetic circuit, designed to be excited by a current flowing through the contact means, the magnetic circuit comprising two lateral branches which extend parallel to the longitudinal mid-plane on each side of the latter and which bound the contact area, the magnetic circuit being designed to produce a magnetic field tending to drive the contact finger through which a current is flowing to the separated position,
• an insulating shield comprising two insulating side walls interposed between the lateral branches and the contact means, the insulating side walls of the insulating shield forming a passage between the contact area and the inlet opening of the chamber,
• wherein
• the insulating side walls of the insulating shield are at a distance from one another which is smaller near the inlet opening of the arc extinguishing chamber than near the contact area, and which is smaller near the inlet opening of the arc extinguishing chamber than the width of the arc extinguishing chamber, so that the passage forms a constriction between the contact area and the movable contact means on the one hand and the arc extinguishing chamber on the other hand, this constriction being at least partially bounded laterally by the lateral branches of the magnetic circuit,
• the pole comprises in addition a first receiving surface of a root of an electric arc, situated between the contact area and the constriction and electrically connected to the first contact means.