DCC Circuit Breaker Location

The best location is near the booster.

Some thoughts from a pure electrical point of view:

1) If you had a voltmeter and measured the track voltage drop during the short circuit, the closer and closer to the location of the short you get, the more the track voltage drops.   When you reach the point of the short, the voltage drop reaches zero.   Likewise if you move the meter closer and closer to the Booster, you would see the voltage go up and up.  The highest voltage being right at the booster.

2)  DCC circuit breakers draw power from their input side***.   During the delay time between the onset of the short circuit but before the DCC circuit breaker has trip, the DCC circuit must remain alive to count down the time to trip and shutdown.  That means the circuit breaker is still drawing power.  It needs some small amount of voltage to run just the processor which typically is about 5V or so.  They do have some capacitance (Keep Alive) to help them limp or bridge through a complete loss of voltage but it is not clear how much hold up time it offers under any and all conditions.

3) With the circuit breaker closer to the  short circuit, the DCC circuit breakers will see a lower input voltage than if it was right next to the booster where the highest voltage is present.   Hence located next to the booster, they is less dependence on the Keep alive function of the onboard capacitor.  Stated another way, the input power is more robust.

4) On large layout I have seen many reported problem with them located near the track farthest away from the booster even with heavy gauge wire.   Inconsistent performance or at worse the booster shutdown instead.    I attribute this to that above voltage drop in combination with the DCC waveform distortion due to the wire inductance.  The simple act of relocating them near the booster has CONSISTENTLY addressed both of the problem.

5) With respect to the features such as fault lights and manual restart buttons, these function are not sensitive to the wiring in any way which means you can locate them remotely.     In other words, even with the DCC circuit breaker located next to the booster, that does not mean you still cannot use the feature they offer at the location of the track they protect.  You just have to run a longer run of small gauge wires.

*** After the circuit breaker trips to isolate the short, the track voltage on the input will recover to normal levels allowing the Keep Alive to recharge during the shutdown period and keep the circuit breaker alive.

01/23/14