With thanks to Sarah Welland, Lindisfarne Information Consulting Ltd.
Archives New Zealand has produced a guide called "making access decisions under the Public Records Act" which covers most questions. Section 5 outlines some restriction examples, which I find particularly useful. The guide also states that restrictions start on the date of the last action on the record, so restrictions start from the date the record was closed, rather than the date of transfer to Archives New Zealand.
If there are records that need to be restricted but are not covered by the examples in the guide, I use the principles outlined in section 6 the Official Information Act 1982- that is, records need to be restricted due to personal reasons, or for reasons of commercial / political sensitivity. Section 6 of the Privacy Act 1993 contains principles relating to personal information. Although these principles apply more to current records, they can be used to help develop further reasoning for restricting personal records.
The next step is to fill out an access authority form which summarises the reasons for restriction, and lists who would need to be contacted in case someone visited archives and wanted to view a restricted record.
Other useful info:
Archives New Zealand's Appraisal Standard lists 4.6: the privacy principle governing appraisal. This states that appraisal shall not recommend destruction on the basis of privacy issues alone. Privacy concerns regarding records should not override other reasons for retaining them. Privacy issues surrounding the retention of records should be addressed through access conditions such as restricted access periods.
Appendix 6 of the Access Standard lists the relevant sections of the Public Records Act 2005 regarding the restriction of public records. Basically the rule of thumb is that all records should be open access as archives unless there is a good reason for restricting them.
The Office of the Privacy Commissioner presented a useful paper which outlines the relationship between the Privacy Act and the Public Records Act.