Circuit protection design when using Passive DCS mode:
Note: More information about the Passive DCS Mode can be found in the DCS O Gauge Companion by Barry Broskowitz (published by MTH).
Here is a system design that I am using for my DCS control system using Passive DCS mode. Passive mode allows for direct connection of AC power to the track entirely bypassing the TIU. Since I have individual relays and individual circuit breakers for control of power to each block the use of Passive Mode greatly simplifies my wiring.
The TIU used in the system is powered using a separate brick via the TIU AUX POWER input. One fixed TIU channel output is used for the layout. Wiring from the TIU output is connected to each track block in a star configuration. No connection to the TIU input is required.
Shielded twin wire communication cables are used for each TIU output connection to a block. The model railroad layout is small and the wiring to each block is under 10 feet.
Power is supplied to the track using a Z-4000 transformer. The layout will be used with no more that 2 engines operating at a given time. The Z-4000 output is protected with a single 10 amp circuit breaker that feeds track power using a 16 gauge wire. Power to each of 12 blocks is controlled via an AIU ACC relay output in combination with an individual 25 amp contact rated relay. Each AIU ACC output only requires about 1/4 amp to power an individual block relay coil so that 20 gauge wiring is used to connect to all AIU ACC outputs.
Block overload protection: Each block relay output is also protected by an individual circuit breaker.
E-Stop: An E-stop protection circuit disconnects 12 volt dc power to each block relay coil thus effectively shutting down all track power to all blocks. The E-Stop system uses a separate wireless controller pendant as well as individual hard wired E-stop buttons mounted around the layout.
The DCS Remote E-Stop is not functional.
Turnout Overload Protection: Each turnout is individually powered via the turnout AUX connection. The AUX power to each turnout is also individually fuse protected.
Note: The AUX powered MTH track turnouts are controlled via the AIU SW outputs. Each AIU SW output only requires about 1/4 amp to power an individual relay coil so that 20 gauge wiring is used to connect to the AIU SW outputs. The turnouts can also be controlled by a separate manually operated miniature pushbutton switch control panel as necessary.
Note: The 12vdc power for the turnout and block relays is also overload protected.
