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wiring, their soldering tags or leads are passed through holes in the card andbent over, after which they are soldered to the foil. This bending and solderingalso serves to fix components of normal size to the card: heavier componentsare further secured by means of clips, retaining clamps etc.Fig. 4, right, shows clearly how the rear edge of the card is shaped as aplug strip to which the printed wiring is taken, and whereby the unit is connectedto a socket strip (type RNV 212) which is fixed to the bay where theunit is to be placed. The unit cannot be plugged into the bay the wrong wayround, as the plug and socket are made non-reversible through an unsymmetrieallyplaced notch in the card and a corresponding protrusion in thesocket. Every plug connexion has a gold-plated contact bent round the edgeot the card and soldered to the printed wiring (see Ericsson Review No.4/1958, page 126, lig. 4): this prevents the socket contacts wearing away thewiring foil and ensures good electrical contact on both sides.Fig. 5 X 2527Unit occupying 3 width modulesThis particular unit has cooling fins for power tran-A bracket is fixed to the front edge of the card: this bracketa) supports any controls or such things as sockets for measuring pointsneeded for fault location,b) supports the front nameplate giving among other things the unit's codenumber, andc) provides fixing points for the case. This type of bracket carrying socketsbut without nameplate can also be seen in fig. 14.To provide electrical screening and to protect the unit from mechanicaldamage and from dust, the unit is surrounded by an aluminium case fixed tothe front bracket. To close the back, a plate of polystyrene or polyester plasticof high impact strength is snapped into the back rim of the case, as may beseen in fig. 3. The case is produced by cold flow moulding and has longitudinalgrooves internally into which the card slides.A completed unit with the construction just described has dimensions excludingthe plug strip of 32.5 X 101 X 198 mm (1.28" X 4" X 7.8"). When placedon edge, 16 such units are accomodated within the width of the bay, and togetherwith their supporting member occupy 3 height modules. The width module forthis type of unit construction is 34 mm (1.34").Fig. 6 X 7787Power supply unit occupying 3 width modulesLeft, frontright, rearThere are also certain possible modifications to this type of construction, forinstance shorter units (see fig. 13, right) or special models such as the signallingreceiver (fig. 4, left) in which the relay is placed outside the case.The dimensions given above are naturally not always sufficient for everytype of unit. Designs have therefore been produced for units occupying two119