The types of contributions you can make to super are (a) Concessional and (b) Non-Concessional.  For more details go to this link.

Concessional Contributions are usually taxed at 15%, but higher tax rates can apply if you exceed the concessional contribution cap.

Additional tax at a rate of 15% is levied if Division 293 of the Income Tax Assessment Act (1997) applies.  This area of the law is complex and may not apply to you if you are an expat working overseas.

The tax rate on Non-Concessional Contributions is 0% because the assumption is that these contributions are made using money that has been previously taxed, which may not always be the case if you are returning from a country where no income tax is levied.

As well as making $110,000 of Non-Concessional Contributions to super each year, you can also use the so-called ‘3 year bring forward rule’ to make up to $330,000 of contributions in one year.

However, you have to take account of your total super balance, and whether you have triggered the 3-year bring forward rule in previous years to determine precisely how much you can add to your super account and when.

If you over contribute, the Australian Taxation Office (ATO) systems will eventually identify the excess contribution and will advise you of how the excess contribution will be dealt with.  The ATO is responsible for administering the superannuation system and ensure compliance with superannuation law.