Look for the latest edition (currently around 11th or 12th, as of 2025). The older editions (3rd, 4th) lack modern safety regulations. If your course requires the 6th edition, that is fine, but for professional work, go modern.

While you might find a free PDF of Electrotecnia on sites like "Freelibros" or "Z-Library," there are significant risks:

The heart of the book. Here, you learn about sine waves, frequency, period, and the crucial concept of phase shift. The explanation of inductive and capacitive reactance is a standout feature.