Everyone needs to take a little refresher in electrical saftey.
1, don't touch unless you know
2, never work on "live" circuits
3, always disconnect the equipment before working on it
4, when working on a phase change rig that has capacitors treat the system as live even if it is disconnected from the supply as capacitors will store a charge for a long period of time
5, use a meter if you done have one get one
6, Pay attention you life depends upon it
7 always use a ground when running a compressor, compressors can short internally to groungd and without a ground path the electricity will use you or your computer to make the connection killing you and the computer...