"Al" wrote in message
...
I have a project for which I use a wall wart with 18VAC (not DC) output.
Is
it safe to leave such an unloaded transformer plugged in for periods of
time? If not, what would be a good solution other than plugging the unit
in
and out. Thanks in advance for all information.

Al KA5JGV

It is fine to leave it plugged in. If it is UL listed it should be as safe
as the millions of them in service.
Unloaded they should not develop as much heat as a loaded one.