Let me amplify THOR73's sound advice - I've been operating a large (2200 feet of track, 124 turnouts) O scale 2 rail layout for 13 years driven by a single NCE command station and 7 wireless ProCabs. Initially I powered the entire layout with one 10 amp booster. As operations intensified I later subdivided the railroad into 2 power districts, and still later 4 power districts - each with its own 10 amp booster. In the coming year I'll I further subdivided one of those power districts into 2 sub-power districts each with its own breaker to isolate operations in the yard and engine terminal from that of the adjacent main line.
I recommend starting with one 10 amp booster and installing additional ones if the combined power draw you experience in actual operations gets close to the capacity of the system. No harm will come to the NCE system if the draw exceeds the boosters 10 amp capacity - it is designed to safely shut down before damage is done. I use DCC Specialties RRampmeters on the output of each booster to observe actual current drawn during operating sessions. These digital meters are designed to accurately measure the pulse width modulated DCC wave form (analog AC meters designed for sign waves provide less accurate readings). Each power districts is further protected by DCC Specialties PSX PowerShield fast acting digital circuit breakers. They self reset when the short is cleared (such as a when an operator forgets to align a powered frog turnout).
There are at least 3 reasons to subdivide the railroad into multiple power districts -
A - real world peak current draw exceeding 10 amps necessitating additional boosters to divide the load.
B- power district track bus wire runs exceeding 75' from the booster. With careful location of the booster(s) relative to track arrangement one can often mitigate bus length. In a simplistic example if you have a 150' point to point run locate the booster in the middle of the route. In the case of very large layouts with multiple boosters they are typically spread around the layout. Note that multiple track busses can fan out from the booster. I must confess that my bus runs were initially far longer than the recommended 75' length - I had no operational issues other than perhaps a slight slow down at the most distant point from the booster due to voltage drop.
C- Minimize interruptions due to derailments/shorts when running multiple trains on separate parts of the railroad. ( eg a derailment in the yard impacting trains running on the main or branch line. If current draw (factor A) doesn't require an additional booster, you can mitigate issue C by splitting the output of a booster into one or more sub-power districts each with its own digital circuit breaker.
Allow me to further endorse the NCE DCC components. They were designed to handle our O scale environment - perhaps in part due to the owner being an O scaler! I've found that the components stand up well to use - (my command station and first throttle are over 20 years old. Over that time NCE has upgraded my components (like the wireless throttle) with new functionality/features as they became available. One relatively new product is their 2 amp self contained PowerCab. It is a complete DCC system in one hand held package that includes the functionality of a throttle, command station, and a 2 amp booster. Standing alone it can run a modest single locomotive operation. I initially use mine to program/test locomotives on the workbench away from the railroad. I later sent it to NCE for a $90 radio upgrade. When not being used on the workbench test track, during operating sessions one the railroad we use it in wireless mode alongside the other NCE cabs - same form/fit/& function.
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