HOW TO CHOOSE TRANSFORMER
To determine the size of transformer needed for a low voltage lighting system, add up the wattage of all fixtures in the system and add 10% for lowvoltage cable and fixtures connections.
If the total load of fixtures is too great, either divide the total load between 2 transformers or use a more powerful transformer.
Select a transformer with 20% higher capacity than total wattage of all fixtures in the system, that allow you to add more fixtures later.