What if the primary coil of a transformer was connected without the iron core and the secondary coil?
Opening up the core will drastically reduce the inductance of the transformer, which will result in drastically increased current for a given AC input voltage. Applying 240V to a transformer with the core opened up may well result in smoke.

If you must do this get yourself a variac so that you can gradually increase the voltage while measuring the current to ensure it doesn't get excessively high.