The present invention relates to a contact assembly and in particular to a contact assembly in which pairs of spaced apart fixed contacts are supports in an electrically insulating body and sets of movable contacts are displaceable relative to the insulating body so as to either interconnect or disconnect the contacts of each of the pairs of fixed contacts.
In one known contact assembly, three pairs of spaced apart fixed contacts are supported in an electrically insulating body. An actuator is displaceable relative to the body and carries three movable contacts. Each of the three movable contacts is associated with one of the pairs of fixed contacts. The actuator is displaceable between two positions. For each of the movable contacts, when the actuator is in one of the two positions the movable contact bears against the associated pair of fixed contacts so as to electrically interconnect them whereas when in the other of the two positions the movable contacts is spaced from the associated pair of fixed contacts so as to electrically separate the fixed contacts. Thus the movable and fixed contacts define three switches which are opened and closed by displacing the actuator relative to the insulating body. It may be that when the actuator is in a first position a first switch is closed (that is to say the fixed contacts of that switch are electrically interconnected by the associated movable contact), the second switch is closed and the third switch is open, whereas when the actuator is in the second position the first and second switches are open and third switch is closed.
In the known contact assembly, each of the fixed contacts is defined by a U-shaped body having a central section supporting a cable clamp and two legs extending from opposite ends of the central section. The legs extend through apertures in the insulating body into a compartment within which the associated movable contact is received between the legs. Given that the movable contact must be displaceable between the two legs from a first position in which the movable contact makes electrical contact with one of the legs and a second position in which the movable contact is electrically isolated from both of the legs the spacing between the legs must be sufficient to accommodate displacement of the movable contacts and to maintain an acceptable separation between the movable and fixed contact when the switch formed by those contacts is open. The spacing between adjacent fixed contacts of different switches must also be sufficient to maintain electrical separation. This sets a limit on the minimum size of the overall assembly and in particular the number of pairs of fixed contacts which can be accommodated within a predetermined volume.
In the known contact assembly, that portion of each fixed contact against which the associated movable contact bears when the switch is closed is provided with a surface treatment (for example of silver) to improve resistance to wear. If a movable contact is displaced against a portion of the surface of a fixed contact which does not have the appropriate surface treatment rapid wear and hence contact failure results. Given that only one of the two legs of the U-shape fixed contact is given the appropriate surface treatment, it can happen that the fixed contacts are inserted with the leg positions reversed as compared with that which was intended. Considerable care must therefore be taken to ensure that the fixed contacts are inserted in the correct orientation and this adds to manufacturing complexity and cost.
It is an object of the present invention to obviate or mitigate the problems outlined above.
According to the present invention there is provided a contact assembly comprising a plurality of pairs of spaced-apart fixed contacts supported in an electrically insulating body, an actuator displaceable relative to the body between first and second positions, and a plurality of movable contacts mounted on the actuator, each movable contact being positioned on the actuator so as to interconnect the contacts of a respective pair of fixed contacts only when the actuator is in one of the first and second positions, wherein each fixed contact has two limbs defining an L-shape, one limb defining a single leg which extends through an aperture formed in a partition defined by the body and the other limb extending to one side of the leg to define a head supporting a terminal for gripping a wire, and wherein each movable contact is displaceable into contact with the leg of each of the respective pairs of fixed contacts on the side of the leg from which the head extends and on the side of the partition remote from the head.
In contrast with contact assemblies in which the fixed contacts are U-shaped, the L-shaped contacts in accordance with the present invention make it possible to accommodate more pairs of fixed contacts in a given volume. It also makes it possible to design the insulating body so that contacts can only be inserted in the correct orientation or, if the position of individual fixed contacts is reversible, makes it possible to readily visually detect the orientation in which a fixed contact has been inserted. Thus not only can the number of contacts within a given volume be increased but in addition the assembly process is simplified.
Preferably, the leg of each fixed contact defines at least one projection which engages behind an edge of the aperture in the partition through which it is inserted so as to retain the fixed contact in position relative to the insulating body. Each fixed contact may be formed from a single strip of metal bent so that the leg extends at substantially 90xc2x0 to the head. The terminal for gripping a wire may be a simple screw received in a thread formed in the head of the fixed contact.
The insulating body may be a snap fit within a casing, the insulating body defining a recess and the actuator being received within the recess so as to be retained between the insulating body and the casing. The actuator may comprise a carrier displaceable relative to the insulating body with the movable contacts being supported by and displaceable relative to the carrier. Each movable contact may be spring biased relative to the carrier to a rest position in which it bears against the carrier and from which it is displaced to a working position when bearing against the fixed contacts. Each movable contact when in the rest position may be inclined to its orientation when in the working position. The actuator may be spring biased relative to the insulating body and the insulating body may carry a label extending over the fixed contact and indicating the normal status of the switches defined by the associated movable and fixed contacts.