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Stoneybridge West Station Track Diagram.
DC Traction Current Feeds.
T
he above diagram shows Stoneybridge West Station Trackplan. Isolating breaks in the track are shown as a green line across the track, single track isolation is used at the end of some sidings to allow locos to stand whilst the rest of the siding is in use. switched traction current feeds are marked as red and black triangles, points (switches) are also coloured according to polarity with all mainline points set for normal through running. By using the point to switch a short section of track approaching it a locomotive could be stopped on the track section that is fed current through the point, if the point is set against the movement of the train (opposing route is set) the waiting loco will not move. This is due to the point switching the rails of the opposing route to carry traction current, the mechanical switching of the point mechanism effectively connects both the running rails of the closed route together providing the same feed to both rails, the voltage on both rails feeding the waiting loco will be at the same potential so the loco will not move until the point is set for the route the loco is standing on, then there will be a potential difference across the running rails and the loco will move when traction voltage is applied to the track. Using a point to isolate a section of track is really a bit of a cheat but it does cut down on the amount of wiring below the layout to some degree, using points to switch traction current relies upon the electrical connection between mating faces of the rails and point blades, points used in this way must be kept scrupulously clean to avoid power transmission failure, this is a bit of a gamble as it is not a case of IF the point will fail but when. Most exhibition layouts are wired so the length of powered track switched through the point mechanism is kept to a minimum with an isolating break as close to the point as is physically possible. Providing seperate current feeds for each section reduces the possibility of power failure through the point affecting passing trains. Some of the longer locomotives and electrically connected multiple unit sets will pass over a short section of dead track but locos shorter than the dead section will stop. The most common cause of locos failing on pointwork is dirt/hair or dust between the point blade and stock rail, causing high resistance or an open circuit. The most reliable method (common on exhibition layouts) is to mechanically switch the polarity of the crossing `frog' (middle of point where two rails cross over each others path) dependant on the direction the point is set with a point motor, this ensures that traction current is available on the point blades even if there is a poor electrical connection between the point blades and stock rail. The joys of model railway trackwork, paint it filthy & keep it clean, You will be rewarded with a layout that looks good and works!.T
he most important thing to remember when placing traction current feeds is to always feed power into the Facing end of a point/switch (the sharp end). Where a loop is created isolating breaks must be included somewhere on the loop and mainline to prevent short circuits, when only one point at one end of the loop is thrown (set to loop) with the other remaining normal (set to mailine). Although this diagram does not show the actual wiring the number of track current feeds for a relatively small layout gives an indication that it is quite busy below the baseboards with the up & down mainline `Busbars' being fed from a Gaugemaster Series D twin track controller (old square box type). The loops, sidings and shed areas will be controlled from a seperate unit with finer slow speed control for shunting manouvres, some sections of track will be switchable to feed from the controller of an adjacent section allowing for smooth operation across boundaries, EG; a goods working powered by `Down Main'(Series D Track 1) pulling off the mainline and stopping in the down loop, once stopped the points are changed for the yard, power feed is switched to the Yard controller (slow/fine control) and the train is backed into the yard whilst the Down Main (Series D Track 1) controller is used to bring the next Mainline service into the station or run a through train whilst the goods train is shunted in the yard. This form of switching sections between controllers is often referred to as `Cab Control', having many advantages over fixed controller systems as it is a very flexible way of controlling multiple lines/trains, the only real disadvantage is the amount of wiring required not to mention a switch for every section capable of switching between the number of controllers you have. By a little bit of carefull design the wiring can be kept to a manageable level. I have found that CAD (Computer Aided Design) is a handy tool when minimising wiring requirements, this can also help to plan wiring runs below the baseboards and can come in handy as a reference when a fault occurs or when modifying the wiring to incorporate new developments.
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