Cindy,
The galvanic destruction of the mc cable would be a very slow process. If there is enough moisture in the interior of the wall space to support the galvanic action, I would expect that the wall itself (drywall) would fail long before the MC cable. It also could be a source of "sick building" phenomena because of the mold that would grow. There is a high school in St. Charles, IL that has been closed for more than a year do to mold problems.
(
http://www.isbe.state.il.us/construction/Headlines%20April%202001.htm#_2.__MOLD)
They don't know how to fix it and may end up tearing the building down. So it is my opinion that if the wall area is that wet there would be much more serious problems then the damage to the jacket of the MC cable.
Don(resqcapt19)
