I have someone who wants me to put a 100amp sub panel in their basement. There is already a piece of number 2 SEU running from the main panel to where he wants the sub panel which is not being used for anything. Is there anything I can do to get an additional conductor over or do I need to rip out the SEU and replace it with SER? Any ideas would be appriciated...

You do not need to rip out the SE, but you will need 4 conductors to the subpanel, 2 ungrounded, one grounded, and one equipment grounding conductor. All of them installed in the same raceway or cable.

Pierre

... You NEED to run SER,...it has 2 phase conductors,a neutral,and a ground...anything less than this is a Code violation..also, DO NOT bond the sub-panel's green ground screw to the enclosure..a separate grounding bar is needed here..
Russ

Thanks for the reply's. I've done a ton of these, but I was hopeing to save some $$$ on the wire by finding a legal way to run only 1 conducter instead of buying the SER since there is already a piece of SEU going to where I want to be.