Current and voltage transformers are vital components in an overall protection technology system. It is therefore important that the transformer is not just seen as a one-off piece of equipment, but is always tested as part of the complete system. Commissioning is an opportune time to demonstrate the proper functioning of current and voltage transformers. The only problem is that there is increasingly less and less time in which to do this. We therefore need to consider how the transformers and the protection system can be adequately tested within a reasonable timeframe. This paper should be viewed as a proposal for how a test plan for commissioning or refurbishing a protection system might look.