Terminal blocks. SE6104a have the newer small green terminal blocks, where two inputs shares a common. SE6104 have older black terminal blocks which have a common for each input.
"Open is as open does." - Forrest Gump "Can't we all just get a Lon?" - Garry Jack "BACnet: integration or interrogation?" - The Janitor "Open protocols? You can't handle open protocols!" - Nathan R. Jessup “What’s that? Aaa… open protocols? Don’t talk about…. open protocols? Are you kidding me? Open protocols? I just hope we can hardwire an interface!” - Jim Mora http://www.youtube.com/watch?v=U7fjDS0jKiE
ALC discontinued the SE6104 and replaced it with the SE6104a. My understanding is they did this so the layout would be similar to some other modules and they could do away with one of the set-up's in manufacturing.
This recession won't be over until we raise a generation that knows how to live on what they’ve got.