IR testing through transformer

[spamwize2]

Hi all need some help, I've got a panel to test 400vac to transformer but after step down 110vac, do i megger it all at 1000v or just ignore transformer and megger at 250vac?

 

[westward10]

If it is an isolation transformer an IR test on the primary side will have no effect on the secondary. IR tests should be carried out at twice the nominal voltage.