Were you seconded to the institution 2?
Question: If a person was working at one institution (a university), but had his office at a different institution, how can this be described in good English?
The sentence "While working at [institution 1], I was located at [institution 2]" smells wrong to me, but I can't figure out a good alternative.
Secondment is on a temporary basis and does not mean a person is working for two institutions at the same time.
What about 'attachment to two institutions and having his base at one of them'?
not a teacher
You've said it - the 2nd institution is the institution where he is based and is affiliated to.