Model Railway Wiring for Wye Tracks How to wire a Y-track on your two-rail layout for automatic operation

Two-rail model train layouts require special treatment of wye tracks and reverse loops. Wiring a wye track (or Y-track) may seem complicated, but if you take one step at a time and check your work, you will have fully automated wye track polarity control and worry-free train operation. Automatic control of the track switches (turnouts) can also be included.
 
[Click here to review reverse loop fundamentals]
 
Here are two examples of how to wire a wye track:

The first system automatically controls the power polarity on the rails, but the track switches are left to manual control.
 
This system, shown at right, uses three Azatrax MRD1 train detectors and an MREV Polarity Controller to control the track power polarity. Instead of the three MRD1 single detectors, you could use three of the six detectors on an MRD6 HexDetex™.
 
Also required is an electrical contact linked to one of the track turnouts. These electrical contacts are available for many types of manual and powered switch controls. Tortoise™ switch machines have two such contacts built in.
 
In this plan there are two junctions, 'X' and 'M', each with two insulated rail joints or 'gaps.'
 
At junction 'M', the 'MS' rail of the main line meets the 'LS' rail of the wye branch, and the 'MN' rail meets the 'LN' rail. Because the 'S' rails meet and the 'N' rails meet, we call this the 'M' junction.
 
At junction 'X', the 'MS' rail of the main line is across from the 'LS' rail of the wye branch, and the 'MN' rail is across from the 'LN' rail. Because the 'S' rails and the 'N' rails are across from each other, we call this the 'X' junction.
 
How it works: Assume a train is moving left-to-right on the main (straight-through) track and it takes the left branch of the switch.
 
It approaches the Y-branch and triggers sensor 2 before reaching junction 'X'. Sensor 2's detector circuit pulls the MX input of the MREV module low, causing the MREV to change the polarity of the Y branch as required so the train can continue without interruption. It is the operator's responsibility to align the track switches.
 
Similarly, when a train travels right-to-left on the main track and takes the branch toward junction 'M', it will trigger sensor 1 before reaching junction 'M'. Sensor 1's detector circuit pulls the MM input of the MREV module low, causing the MREV to change the polarity of the Y branch as required so the train can continue.
 
Now suppose a train comes from the Y-branch at the top of our track plan. It can take one of two tracks to join the main line. The train will trigger sensor A before reaching the switch. The output signal of detector A (Q1) is routed through an electrical contact on its way to the MREV module. This electrical contact is linked to the switch points. Detector A will connect with MREV input 'LX' if the switch is aligned with junction 'X', or it will connect with MREV input 'LM' if the switch is aligned with junction 'M'. The MREV will change the main track's polarity as needed so the train can move from the Y-branch to the main line without interruption. It is the operator's responsibility to align the track switches.

MREV Polarity Controller	$32.50
MRD1 Single train detector • Includes one infrared sensor pair (IrLED & photo-transistor)	$16.95
Accessory power supply, PS906 • Regulated 9vdc, 650mA, slim plug-in • One supply will power a dozen Azatrax modules	$9.50
Package for Wye Track automation, without switch control Everything needed for the wye track polarity control: • MREV polarity controller • Three MRD1 single detector with IR sensors • One PS906 9vdc regulated power supply	$85.00

Automatic control of the turnout is possible, as shown in the next system below.

This diagram shows an MRD2 dual train detector taking the place of two MRD1 single detectors. This adds automatic control for the upper track switch (the wye turnout). This system is fully compatible with DC, DCC and AC layouts.
 
The MRD2 dual detector will control either solenoid 'snap' switch machines or slow motion switch machines. Note that an electrical contact on the switch machine is not required.
 
Wire the switch machine so the switch points are aligned for the 'M' junction when sensor 1 is triggered. If the points align the wrong way, swap the connections to the switch machine.
 
As shown, operation of only the wye switch is automated. The other two turnouts can be automated by adding an additional MRD2 dual detector for each turnout.
 
The MRD2 and MREV circuits have non-volatile memory. They remember the switch position and polarity settings when layout power is turned off.
 
Detector circuits and the MREV polarity controller require a power supply, 8 to 15 volts AC or DC.

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