Electric circuit breaker device

An electric circuit breaker device comprising:

• a housing including an accommodating space inside, the accommodating space extending in one direction and including a projectile accommodating portion formed at one end side and an arc-extinguishing region portion formed at the other end side;
• an igniter provided at the housing;
• a projectile accommodated in the projectile accommodating portion and configured to be projected from the projectile accommodating portion toward an arc-extinguishing region portion side along the accommodating space by energy received from the igniter;
• and
• a conductor piece provided at a housing body of the housing and forming a portion of an electric circuit, the conductor piece including, at a portion of the conductor piece, a cutoff portion to be cut off by the projectile, the cutoff portion being disposed crossing between the projectile accommodating portion and the arc-extinguishing region portion, wherein
• the projectile includes, on the one end side, a piston portion, and, on the other end side, a tubular cylindrical rod portion extending directly from the piston portion and defining a cutting-off surface configured to cut off the cutoff portion during actuation of the igniter,
• the cutting off surface has a circular shape, and
• of the conductor piece, at least one of a first surface facing a projectile accommodating portion side or a second surface facing the arc-extinguishing region portion side is formed with a cutting-off assisting groove at a predetermined expected cutting-off position where the cutoff portion is pressingly cut by the cutting-off surface during actuation of the igniter, the cutting-off assisting groove having a circular arc shape conforming to a contour of the cutting-off surface as seen in a moving direction of the projectile,
• the cutting-off assisting groove is formed as a V-shaped groove of which a cross-sectional shape along a thickness direction of the conductor piece is V-shaped, and
• an outer circumferential edge of the cutting-off surface and an inner circumferential edge of the housing body are provided at positions substantially overlapping a bottom portion of the V-shaped groove in the moving direction of the projectile.