Short Circuit protection with DCC : LUSENET : Wiring for DCC : One Thread

In DCC literature, I have seen it written that failure of short circuit protection to kick in can be attributed to bad wiring. I am trying to find out what this means. We have a MRC Prodigy with the 8 amp booster, and it does not shut down when shorts occur. We have burned up several turnouts because of this. We are implimenting insulated gaps to keep the shorts from occuring, but why doesn't the unit shut down as it should? As far as I can tell, there is nothing hinky about the way the layout is wired, just a standard two-wire bus going around the whole thing, no common rail or anything like that. Dale

-- T. Dale Mings (, July 11, 2004



Just as a sanity check, make sure that your booster is operating correctly. Take a pair of pliers and directly short out the booster at its output terminals. If this doesn't work, you may not have your booster set up correctly. See the manual. Otherwise, it may need repairing.

Assuming shorting out the booster directly works, adequate wiring means using at least 16 AWG wire for your buses. I like using solid wire for my buses as it is easy to strip in the middle to add track feeders. Therefore, I use 14 AWG or heavier house wire.

Keep the track feeders, ideally about 6" long.

Lastly, if you have bus runs of 30' or more, Don Vollrath offers the following:

Twist the track bus wires together, 1 turn per 1-3 inches. Put an R- C load of 100-150 ohms, 1/2 watt resistor and 0.1 uFD, 50V (or higher V) capacitor in series at the end of each bus run to help suppress ringing. None of this is mandatory, but each step will help minimize later problems sometimes encountered with larger layouts.

-- Don Vollrath

-- Allan Gartner (, July 11, 2004.

AND be sure that your power supply (an AC transformer or DC power supply) to the Prodigy equipment can supply the 8+ amps needed to cause the booster to trip. The plier or 'coin' test that Allan mentions is one way to test the integrity of your equipment and wiring to safely shut down for self protection. If it doesn't shut down on a track short circuit everywhere on the layout, minor melt- downs (or worse) can occur.

-- Don Vollrath (, July 12, 2004.

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