The HPAC test is typically performed between all primary windings connected, and all secondary windings. A DCR test can be used to confirm that the connections are good, before the HPAC test is executed, to ensure that any HPAC PASS is valid. HPAC can also be used to verify the isolation between windings and a screen or a core. However, If the screen or core is not properly connected during HPAC test, the AT5600 could give a false PASS, as the unit would (correctly) measure a very low current as there is no connection to the screen or core.
As the screen (or core connections) are to a single node, it is hard to confirm that the screen or core is connected, as you cannot perform a DCR test as you can with a standard winding with 2 connections.