The answer depends on what you're using to power your layout. Please post the model numbers for your transformer(s) and any other power control devices you're using such as the Legacy Powermaster or TPC and which models. If you're also using MTH DCS, which units?
Other needed information would include how many independently wired track loops you have and how many locomotives you plan to run on each loop at the same time.
This information will provide a good starting point to answer your question.
