Faraday Shield for isolation transformer

[Kevin Walker PE]

Greetings
I have a question concerning Faraday shielding for transformers. We
have a specially built "old" isolation transformer with an equivalent
turns ratio of 1:1. It is toridial in design. It is part of an
isolation circuit that has an incredibly low noise floor. It appears
that the primary is wound onto a wrapped shield of some sort, with the
secondary underneath. Its actually a bit difficult to see because of
all the epoxy. So far, we have been unable to un-wind anything below
the primary. So, my question is, how are Faraday shields incorporated
onto a “CT” type of transformer. Would the secondary
normally be wrapped under a shield. We intend to build several of
these for our own in-house use, and would very much like to retain the
very low noise floor that we have in these old units. Any and all
responses are most welcome.

thanks....Kevin Walker