PSXX-1

Hey Guys, My DCC Specialties PSXX-2 Circuit Breakers finally arrived on Thursday 2/10/2022.  In DCC Specialties drawings of how to hook the PSXX2 up, it shows gaps in both rails.  I have always simply gapped the A rail (RED).  They are showing Gapping the B Rail (Black) also.  Is this really necessary?  It seems to me to be adding extra work to the process.  If is is necessary, could you please inform me of why it is needed? Thank you!...............Mark D

Mark: The configuration you suggest is called common rail. Since we do not know the details of a specific layout, we recommend completely isolated blocks because they will result in reliable operation regardless of the layout size or number of boosters, and more or less force you to wire the DCC buses correctly with a "speaker wire" [two parallel wires molded next to each other] or twisted pair to each block.

You definitely should NOT use common rail if you are using more than one booster or if you have DCC bus runs longer than about 20 feet. With more than one booster, small voltage differences between the two boosters can cause a large current flow in the common rail. By breaking the "common rail" [i.e. making each power district completely isolated], you prevent this current flow. With long bus runs, you want to use "speaker wire" or twisted pairs to keep the wires physically close together. This eliminates the inductance of the wire because the current in both wires is equal in magnitude and opposite in polarity. Hence, the magnetic fields around the wires cancel each other and there is little to no inductance. If you use common rail, the currents in the two wires are no longer equal and opposite, so there is significant inductance in the wiring. This will cause problems with the DCC waveform and can cause damage to decoders from stored inductive energy.

If you are only going to use one booster ever, and have a relatively small layout where all wire runs less than about 20 feet, then using common rail is OK [we still do NOT recommend it]. If you are using common rail, then the common rail MUST be connected to J1-1 and J2-1 of the PSXX.