Mains Transformer Help

There are some main characteristics to recognize the transformers primary and secondary windings.

1. Most of transformers have printed or hand written on it the primary winding (e.g. 230Vac) and secondary (e.g. 24Vac/3A) but if not here is how to recognize which side connects to the 230Vac mains.
2. The primary wire is fine (0.1 - 0.5 mm diameter - according the power) but the secondary winding wire is heavy (0.5 -1mm or more diameter).
3. The primary winding consists of  many turns (thin wire) usually some hundred or thousand, because the current on it is low (some milliamps).
4. The secondary winding consists of  some decades of turns (thick wire), because the current on it is big (some amperes).

  Here is a diagram showing the transformer connections.