Body cord

In fencing, a body cord serves as the connection between a fencer and a reel of wire that is part of a system for electrically detecting that the weapon has touched the opponent. There are two types: one for epee, and one for foil and sabre.

Épée body cords consist of two sets of three prongs each connected by a wire. One set plugs into the fencer's weapon, with the other connecting to the reel. Foil and saber body cords have only two irregularly sized prongs (or a twist-lock bayonet connector) on the weapon side, with the third wire connecting instead to the fencer's lamé. The need in foil and saber to distinguish between on and off-target touches requires a wired connection to the valid target area.

The three wires of the body cord are known as the A, B, and C lines. At the reel connector (and both connectors for Épée cords) The B pin is in the middle, the A pin is 1.5 cm to one side of B, and the C pin is 2 cm to the other side of B. This asymmetrical arrangement ensures that the cord cannot be plugged in the wrong way around.

The A line is the "lamé" line, the B line is the "weapon" line, and the C line is the ground. Although it works somewhat differently for each weapon, a valid touch always involves the connection of the A and B lines. In all three weapons, the C line is connected to the body of the weapon, and sometimes (normally in high-level competition) to the fencing strip as well, which must be made of metal in this case.

In foil, the A line is connected to the lamé and the B line runs up a wire to the tip of the weapon. The B line is normally connected to the C line through the tip. When the tip is depressed, the circuit is broken and one of three things can happen:

In Épée, the A and B lines run up separate wires to the tip (there is no lamé). When the tip is depressed, it connects the A and B lines, resulting in a valid touch. However, if the tip is touching your opponents weapon (their C line) or the grounded strip, nothing happens when it is depressed, as the current is redirected to the C line. Grounded strips are particularly important in Épée, as without one, a touch to the floor registers as a valid touch (rather than off-target as in Foil).

In Sabre, similarly to Foil, the A line is connected to the lamé, but both the B and C lines are connected to the body of the weapon. Any contact between your B/C line (doesn't matter which, as they are always connected) and your opponent's A line (their lamé) results in a valid touch. There is no need for grounded strips in Sabre, as hitting something other than your opponent's lame does nothing.

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Wikipedia