People often get confused between layout size and power capacity needs. The size of your layout has an impact on the wire size used for the track bus and overall wiring practices used when building your layout. To read more about proper DCC wiring go here: http://www.wiringfordcc.com/track.htm
These examples below are for the 2 amp Power Cab starter set. A maximum of three additional cabs can be added for additional locomotive operators.
DCC Systems are selected based on locomotive and operator capacity needs. The general rule of thumb for HO scale locos is .5 amps per loco, in N-scale use .25 amps per loco. You only count the number of locos being used, not parked.
The Power Cab is a complete self-contained starter set with a 2 amp capacity and a DCC (AC-PWM) track output voltage of 13.8 volts. The Power Cab is suitable for Z, N, HO, S, and On3 scales. Using the numbers above we can guesstimate that the Power Cab has the capacity for about 4 HO-scale locomotives or 8 N-scale locomotives running at the same time. You count locomotives on the track but exclude the ones not running. For more reading on How many locos you can run click here, You can add up to 3 additional NCE cabs of any kind for more operators or locations.
The possibilities for upgrades and expansion after the Power Cab is installed are endless. Go here for more information on what you can do after installing the Power Cab.
If you know upfront that you will need 5 amps or more of capacity, or you will need more than four cabs, or wireless is a requirement, the best place to start is with the PH-Pro 5 amp starter set. Then add 5 amp boosters (PB5) for more locomotive capacity as needed.
Your layout should be divided into power districts with short-circuit protection. Use an EB1. go here to learn more
Do not attempt to run any O-scale or G-scale equipment with the Power Cab. These larger locos require higher track voltage (18v) and higher current capacity (10 amps). This is much more than the Power Cab can deliver.
For no-hassle layout wiring kits go here: NCE Layout Wiring Kits. =============================================================
More Information for Larger scales:
Do not attempt to run any O-scale or G-scale equipment with the 2 amp Power Cab. Standard O-scale and G-scale require the use of our 5 or 10-amp system regardless of locomotive size or layout size.
With O and G-scale the discussion involves increased track voltage AND increased current capacity. The combined values of both are what give you the power (current capacity) to run larger equipment. Most O and G-scale equipment are designed to be used at a minimum of 18 volts of track voltage. You will need to know the recommended track voltage for your equipment and the total current capacity needed for all locomotives. The Power Cab is a 13.8 volt / 2 amp / 24-watt system. It is completely unsuitable for any large-scale equipment regardless of size. The Ph-Pro 5 amp System is a 5 amp system. The maximum power supply that can be used is 16VAC / 28VDC. The output of the box can be adjusted to as high as 22 volts and will run large-scale equipment with the right power supply. But it will have a LOWER current capacity. Use our P515 5amp 15vAC Transformer power supply. The PH-Pro box comes preset for an output of 14v but using the dial to adjust the output between 18v and 22v is a simple matter.
However, be aware that increasing the voltage output reduces the current capacity below 5 amps.
It is simple multiplication using the official system rating of the 5amp Ph-Pro system box: 15-volt output x 5 amps = 75 watts of power maximum output.
using 18v output reduces the current capacity to 4.16 amps
using 20v output reduces the current capacity to 3.75 amps
using 22v output reduces the current capacity to 3.4 amps
Do not attempt to run any O-scale or G-scale equipment with the 13.8v / 2 amp Power Cab.
For information on the 10 amp system: https://ncedcc.zendesk.com/hc/en-us/sections/200226775-Power-Pro-10-Amp-Systems
To read more about wiring go here: http://www.wiringfordcc.com/track.htm
Main DCC track bus wire size recommendations:
For a complete with everything no brainer layout wiring kit go here: NCE Layout Wiring Kits.