Planning the Model Railroad
Sub Roadbed and Track Wiring Setup


By Kevin C
Once I have finished drawing the full size track plans of the layout that I want to use and before I set out the track, I usually work out the switching locations and signals etc. and mark these on the plan. Also, I plan the road crossings so that I can install the crossing light switching in the right place. Then I draw the wiring circuits on the plan in different colors as it is very easy to miss a connection when setting out the track. Recently I was given a quantity of computer data cable with four pairs in the following colours
• Orange - Orange White

• Brown - Brown White

• Blue - Blue White

• Green - Green White

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laying track sub roadbed

As these wires are twisted together and have a plastic former to separate them and are housed in a blue plastic cover. They are easy to use. If more than four wire pairs are required simply add another cable and label them as 1, 2, 3, 4, etc with a fine permanent pen on the plan and cable. I also mark the relays the same way if more than one relay is required. By taking measurements from the plan I make up each switching circuit on the work bench and when completed I label them and the plan then they are ready to install as the track is laid.

Add Track Sub Roadbed

Using a second set of plans transfer the curves sidings etc to the timber you intend to use for the track sub bed, and you can use a number of different woods for these from plywood to MDF or even timber planks, however you will need to cut the curves from plywood or MDF. Leave gaps if you intend to have bridges and take a small notch out of each end so that the bridge will sit at the correct height allowing for the thickness of the cork road bed so that the track does not bend upwards. I lay the cut pieces over the table frame and secure them with speed screws (double the thickness of the board). I use the ones that take the number 2 square drive. Also an electric screw driver is a good tool to have.

The curves I cut on my band saw. (A jigsaw is equally as good.) I cut these 20mm each side larger than required as then I have a good edge to attach the scenery to. Once I have finished these I cut the actual track bed from 9 mm MDF or ply wood and shape the sides to represent the raised track ballast. The first part of the shaping is done with a spoke shave or wood rasp then sanded with a 150 grit sand paper taking care at the joins so that the edges match and there are no sharp edges. Secure these to the track sub board with PVA glue keeping the equal spacing from the edges with smaller square drive screws i.e. 20mm x 8. I space these at 150 mm. Next cut the trenches for the reed switches so that they sit in the trench just below the top of the board and drill a hole at each end to take the wires under the track bed as per your plan and glue the reed switch in place with just a drop or two of PVA glue.

Then I lay the cork track bed along the entire length of the track just securing it with PVA glue. Sticky back cork tiles cut to size are a good substitute. The track pins will push through the rail tie and the cork. I then use a nail punch and small hammer to gently tap them home as I lay the track, being careful not to break the track ties and distorting the track.

Take your time and get the joins right first time as these joins if not done properly it will be a point where most derails will occur. If using flexi track, ensure that the straights are indeed straight and the curves are even. Cut only one rail for the isolation points for your signals and use plastic rail joiners to hold these in position making sure there is enough gap so that the rails do not touch. (Most plastic rail joiners have a spacing section in them.)

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Signals can be set at eye level for the engine driver or low to the ground in marshalling yards once the signal is in place it can be held with a drop of PVA glue. I paint the poles with a rust coloured paint. Each LED can be bought with a current limiting resistor for 12 volt operation and these must be used on each wire when connecting to a relay or switch. A double throw double pole switch or relay is needed to operate the signal. It should be wired so that the red LED is on when the power is off at the rail to stop the train. You can file the end of the rail pole where it pokes through the base board to take a chocolate block connector with three connectors, the middle one for the pole and one at each end to make the connections to the thin wire after scrapping the enamel off and you can use a heavier wire to connect to the relay and resistor, and the middle connector for the negative or common wire.

track roadbed

Power and Track Wiring 

Once the entire track is laid I put in the wiring and I use aluminium cable clips (the same that electricians use for house wiring), to hold the cables in position, making sure to use longer ones where the most cables need to be. Lighting, animation, signal and control cables are run together and clipped in place.

I usually keep track power cables separate and these follow the track with lighter wires connecting power all parts of the track so that continuity is maintained, or via the signal relay for track control. For connection to the main cable I keep the wire connections 3 inches apart so that they cannot flash together causing a short circuit.

A small hole right next to the track is best so that these wires pass through the holes which helps keep them in place. The bared end of the wire is bent at right angles so that it lays in the neck of the rail. A point to watch here is the correct connection of positive and negative to the track to avoid a short circuit. It is easier to hide these smaller wires in the scenery and soldering them to the outside of the track so that there is no interference with the wheel flanges, filing the solder so that it is lower than the head of the track so that the wheels do not bump as they run over these sections as this will cause derailments.

Treat all connections this way and those coming from the reed switches can be soldered to the relay making sure that the connections are right. There should be a wiring diagram with each relay showing each connection. To make a relay self latch you use one set of contacts to supply power to the coil of the relay so when activated it keeps the power to the coil on and the power running through another relay that will disconnect the power when activated by the second reed switch returning the relay to its normal position. Relays can be taped together in batches if a number of them are required and then taped to the bench frame work with a good quality insulation or duct tape.

model railroad wiring

Fig 1 Self latching relay circuit with extra relay reset circuit with reed switch activation.

Red wire +12 volts positive

Black wire -12 volts negative

Blue wire + 12 volts latch circuit.

Relay 1 contacts normally open will close when activated. Relay 2 contacts normally closed will open when activated thus resetting relay 1 by shutting off the power to relay 1’s latching circuit.

railway scenery 

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The basic relay circuit can be used for signals and track isolation, railroad crossing signals etc. although if used for railroad crossing you will need to add two more reed switches wired in parallel with those shown and these need to be set up at a distance where the train has cleared the road crossing. If done properly they will work with trains running in either direction. A led flasher circuit would need to have the crossing lights working.

On my set I use an NE555 timer integrated circuit on a small printed circuit board working on 9 volts DC so it is recommended that a separate power supply is used. I use a mains voltage to 9 volt battery eliminator bought from a local electronics store, or an old mobile phone charger providing the output is 9 volts DC.

track wiring

Fig 2. Circuit for NE555 flasher for railroad crossing lights.

This circuit will run 4 LED’s with two in parallel where 1 is shown in the circuit (make sure they both are connected as shown in fig 3.) I also recommend that the I.C. have a socket as soldering heat could damage the I.C. Pin 1 has a dot next to its pin on the I.C case. Flash rate can be changed by lowering the trigger resistor (39K) to 27 K. For HO gauge I use 3mm LED’s.

The Ne555 is ideally suited for this operation being a timing I.C. The two flashes will maintain equal timing. I also used this circuit to simulate traffic lights on an intersection by increasing the value of the trigger resistor and making the trigger capacitor to 10 uf. I could slow the rate to one a minute for each LED and by adding a variable resistor you can change the rate to suit. However it does not have the yellow light.

LED wiring

Fig 3.  Two red LED’s connected in Parallel. Make sure only one of each is in each light standard

The use of electronics is increasing in model Railroading and can add more realism to your layout. DCC is becoming more common place and with the realistic sounds it is making the model world more and more like a full size railroad in miniature. There are many excellent books on Electronics in Model Railroading at most hobby shops and preferred book stores.

Most parts these days can be bought online or direct from electronic retailers. The printed circuit board can be sourced from a printed circuit board manufacturer who will be able to make up the circuit on the board and screen print the board for placement of components but this service may not be cheap. I recommend that a tinned board is best as it is easier to solder the components. A cheaper option is to use a premade bread board or matrix board, but knowledge of how to set these up would be required. I would recommend the use of PCB screw connectors to attach wires to the printed circuit boards and these are available in 2 and 3 connector blocks quite cheaply and that can be mounted side by side on the board for multi connections.

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