Line and Cord Equipments. The parts of the switchboard that are individual to the subscriber’s line are termed the line equipment; this, in the case of a magneto switchboard, consists of the line drop and the jack together with the associated wiring necessary to connect them properly in the line circuit.  The parts of the switchboard that are associated with a connecting link—­consisting of a pair of plugs and associated cords with their ringing and listening keys and clearing-out drop—­are referred to as a cord equipment.  The circuit of a complete pair of cords and plugs with their associated apparatus is called a cord circuit.  In order that there may be a number of simultaneous connections between different pairs of lines terminating in a switchboard, a number of cord circuits are provided, this number depending on the amount of traffic at the busiest time of the day.

Operator’s Equipment. A part of the equipment that is not individual to the lines or to the cord circuits, but which may, as occasion requires, be associated with any of them is called the operator’s equipment.  This consists of the operator’s transmitter and receiver, induction coil, and battery connections together with the wiring and other associated parts necessary to co-ordinate them with the rest of the apparatus.  Still another part of the equipment that is not individual to the lines nor to the cord circuits is the calling-current generator.  This may be common to the entire office or a separate one may be provided for each operator’s position.

Operation in Detail.  With these general statements in mind we may take up in some detail the various operations of a telephone system wherein the lines center in a magneto switchboard.  This may best be done by considering the circuits involved, without special regard to the details of the apparatus.

The series of figures showing the cycle of operations of the magneto switchboard about to be discussed are typical of this type of switchboard almost regardless of make.  The apparatus is in each case represented symbolically, the representations indicating type rather than any particular kind of apparatus within the general class to which it belongs.

Normal Condition of Line. In Fig. 240 is shown the circuit of an ordinary magneto line.  The subscriber’s sub-station apparatus, shown at the left, consists of the ordinary bridging telephone but might with equal propriety be indicated as a series telephone.  The subscriber’s station is shown connected with the central office by the two limbs of a metallic-circuit line.  One limb of the line terminates in the spring 1 of the jack, and the other limb in the sleeve or thimble 2 of the jack.  The spring 1 normally rests on the third contact or anvil 3 in the jack, its construction being such that when a plug is inserted this spring will be raised by the plug so as to break contact with the anvil 3.  It is understood, of course, that the plug associated with this jack has two contacts, referred to respectively as the tip and the sleeve; the tip makes contact with the tip spring 1 and the sleeve with the sleeve or thimble 2.