A simple EPA (ESD Protected Area) consists of 3 things:
- wrist strap
- antistatic mat
- common point ground
Wrist strap and antistatic mat both should grounded to the common point ground.
You might think: just put a resistor between Common Ground and mains earth...
ANSI/ESD S6.1, section 6.4.2 recommends: The resistance [...] from the common point ground to the AC equipment ground shall not be greater than 1 ohm.
Both plans below don't follow ANSI/ESD S6.1, because i think the path between antistatic mat and mains earth should NOT be a low impedance path.
And if there should be a resistor between an dissipative surface (like an antistatic mat) and mains earth for user safety, then there should be a resistor between a conductive surface (unpainted inside of a PC case) and mains earth too.
In theory, is one plan more preferable over the other?
Plan A: only 1MΩ between wrist strap and common ground. Thus discharging takes less time. Therefore (maybe?) less chance of a potential difference between wrist strap and the PC (with ESD sensitive hardware inside) and less chance of an ESD event.
Possible disadvantage of plan A: because the user is constantly charging himself (by moving) and discharging to the common ground, the common ground will be bouncing more than it would in plan B. (Please correct me if i'm wrong.)
Both plans are easy to execute.