How is secondary (Patient) leakage current tested?
Grounding the Transformer shield via the top platter ground connector and measuring leakage current between primary and secondary will give you the secondary current (the patient current)
It is also advisable to do the following leakage current tests:
1. Using the configuration in the AT user manual with the shield shorted to secondary
2. Grounding the shield as above
This ensures that a possible short or damage in insulation to the shield will be caught.
This can be achieved using an OUT test using a relay to connect the shield to either ground or to the secondary.