Existing 3-way circuit trips breaker
Grrr  hahaha grrr hahaha grrr 
aaa
Solved - and I have a very red face.  Turns out that several years ago I replaced a light bulb in one of the pendants.  When it did not light up, I determined that the base of the bulb was not making contact with the pin in the seat of the socket.  To help it out I put a penny in the socket and presto - things worked (foolish me!).  Turns out that the penny moved to one side when a new bulb was installed and gradually made contact with the socket wall - not good!

So, after a breaker swap, two 3-way switches and a lot of bafflement, I have only myself to blame.  I'm lucky indeed that was all that happened, lesson learned as things could have turned out much worse.  Enjoy the laugh - it's on me!