Catholics may not receive communion at an Episcopal or any
Protestant service because it is an expression of unity of faith with
that body, when we do not share the same faith with them.
It would essentially
be a lie. While we agree on some things, there is no full communion of
faith, and none, at all, when it comes to the Eucharist because they do
not possess the Eucharist.
There is no Real Presence of Christ in their sacrament.
receiving communion in denominations that believe differently about the
Eucharist is a way to be respectful of the beliefs of others and to bear
witness to our own faith.