Osmany,
You might want to check this out. this guy David Pascoe covers many subjects and is a good starting point in getting yourself educated as to how systems work the way they do and some of the pitfalls of the untrained attempts of well meaning boat owner/repairmen who try to do the right thing, but just don't know what they need to to do the job right.
Good luck.
Here's the URL:
http://marinesurvey.com/yacht/Electr...AC.htm#Grounds