East of the Blue Ridge

Chronicles of an On30 quarry railroad

February 2009

Entering the Loop

Track construction on the P&EBR has extended up the mainline to the town of Ariel Church.

The turnout circled in red controls the entrance to the second reverse loop on the layout. A train coming up the mainline could take one route through this turnout and eventually return back to the turnout on the other route. The other end of the mainline also forms a loop. Running from loop to loop will allow trains to run continuously without ever coming to the end of the line. Controlling the entrance to the loop and the polarity of the electrical current in the rails requires some special circuitry and wiring.

A junction in the power buss provides power to a PSX-AR, which will immediately correct the polarity of the reverse loop power block whenever a locomotive enters it.

The PSX-AR is mounted on the benchwork under the Shops Yard. Power comes in from the junction in the power buss on the right, and the power buss for the reverse loop block goes out to the left.

The reverse loop power buss runs through the Piedmont Mill section of the layout. Pulling these wires was the first new construction on this section of the layout in years.

The reverse loop power buss runs through a barrier block under the middle of the Piedmont Mill section. The block is accessible from inside the bookcase that supports the section. The barrier block will provide junction points for the feeder wires in this section.

Once the buss wires had been pulled and the rails gapped for the reverse loop, I moved on to the automatic controls for the turnout at the entrance to the loop.

This is the turnout that forms the entrance to the loop and the Tortoise switch machine that powers it. The Tortoise is in turn controlled by the Hare stationary decoder attached to its electrical contacts.

The Hare is connected to the power buss and has an address that can be selected on a locomotive engineer's throttle. The engineer can then throw the turnout using buttons on his throttle. Throwing the turnout will cause the Hare to switch the polarity of the turnout frog to match the selected route.

The Hare also has the capability of throwing the turnout automatically if a train is approaching with the turnout set against it. In order for the Hare to sense which direction a train is approaching from, trigger rails have to be wired into the approaching tracks.

Trigger rails are short sections of rail wired directly to the Hare. When a locomotive runs onto a trigger rail, the Hare knows a train is approaching on that track, and will automatically throw the turnout if necessary. Having trigger rails controlling the turnouts at the entrances to both loops on the layout means "hands off" continuous running is possible.

The trigger rail wires are routed through this switch which will allow me to override the automatic turnout control function.