What is Common Rail Wiring?
To understand Common Rail Wiring, we must first understand common wiring. If you ever heard the term "Common Ground", "Common Rail" is the model railroads wiring equivalent.
Common rail wiring is a wiring technique mostly used on large layouts such as club size where it offers a big wiring reduction advantage. Most people have never heard of it before unless they were connected with a large layout at one time or another. None the less, Common Rail wiring has been around for a long time.
Common rail wiring uses a single master heavy duty gauge wire that is shared by all electrical devices powering the layout as part of their common current path. The wire follows and feed the common rail all over the ENTIRE layout at the same time. This puts the common rail and common rail wire it is connected to electrically in parallel.
Common Rails advantage: Depending on the circuit, common rail wiring drastically cuts down on the number of wires you need to run around the layout by almost 1/2.
Two understand this advantage, one need to review how a layout is normally wired.
Two wires from a booster or DC power pack must feed both rails of the track all over the layout. There may be some switches in the path but eventually the DC power pack or booster will feed into two long wire running side by side forming a track bus connecting to the track with feeders all over the layout.
With common rail, One wire from the booster or DCC power pack is run directly to the nearest common rail wire. Typically a short distance and your done. The existing common rail wire does the rest. However the second wire must still find its long way around the layout to power the none common rail. This is why it only cuts the amount of wiring some what in half to get things up and running. Less wiring, faster installation.
If you add a second DC power Pack or booster, the wiring is the almost the same as the first DC power Pack or Booster. However there is some additonal control wiring required to prevent the DC Power Pack or DCC booster from coming into direct parallel contact with each other at the track level. This isolation is typically done with "block wiring" in the DC days where on selected which DC power pack power which block of track. With DCC, the blocks are permanently assigned to one booster or the other in the creation of booster Power Districts. The isolation is all done on the NONE common rail side of the track.
Common rail wiring is not recommended with DCC because of the potential for a second common above and beyond the common rail. This creates two commons which can create electrical problems.
To learn more go here: Booster Ground/Commons
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