Recommendations for AutoCAD add ons electrical and plumbing

What is your recommendation for a good add on to do electrical schematics? I need one that has all the symbols, too. What program do you think is best to use for piping schematics? I will also
need to do isometric schematics and need all the appropriate symbols. I do not want to spend any more money than necessary but would like to get a quality piece of software. Thanks in advance, Carolyn
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