What safety precautions should I follow when plugging in the HP Z420 Workstation?

Plug the power cord into an easily accessible AC outlet and always disconnect power by unplugging the cord from the AC outlet, not from the computer. You must use a grounded (earthed) three-pin outlet and must not disable the grounding pin, for example by attaching a two-pin adapter, as it is an important safety feature. (Page 16)