It requires just 4 connections, two to the main line and two to the loop.

In addition it functions as a circuit breaker for the reverse loop.
Recommended for DCC systems from 1 to 10Amps
Features of the AR10 Automatic Reverse Loop Controller:

• Automatically controls polarity of DCC reverse loops
• Provides short circuit protection for loop
• Ready to run without any programming
• Trip current adjustable 1 to 10 Amps
• Easy hookup using screw terminals, no soldering
• Solid state design provides silent, reliable operation
• Status indication LED
• Additional output for remote LED
• Automatic or manual reset after short circuit shutdown
• Adjustable short circuit response time
• We also carry the DCC Specialties PSX-AR.