Windows 7: ESD precautions advice being sought.

I know it is important to protect your PC from ESD when ever you either upgrade or do anything inside the PC, the thing is though I am not sure what best practise is or am I doing it correct. I currently only have a wrist strap but was looking at buying a ESD floor mat as well as a mat for the desktop.

What I want to know first of all is if I attach myself to the PC while the power cable is still plugged in but with the power switch in the off positition (for obvious reasons) will the PC still be earthed or is the earth connection broke as the live connection it. Also is it neccesarry to actually have yourself and the PC earthed when you are just using a wrist strap.

Secondly, when you use floor mats, desktop mats as well as a wrist strap do you all have to be connected to each other or is it fine as long as your connected to the PC and the floor mat and the floor mat and the desktop mat are earthed? And does it matter if the 2 different mats are earthed to 2 different earth points i.e. a plugs/socket?

Best to earth all.

All your earth points in the wall sockets are linked.

Yes they are, but with regards to having to be connect to them providing that plugs are all on the same main then it's not important?

Also what about just being attached via wrist strap, is the PC still earthed with the power switch in the off position?

The PC is still earthed regardless of the power switch, because the switch only changes the "live" wire (Actually having said this, 2 pronged power plugs like http://www.leadsdirect.co.uk/images/...ng%20300px.gif will NOT be earthed, only 3 prong such as http://www.leadsdirect.co.uk/images/...ng%20300px.gif will be, and therefore 'safe')

It doesn't matter where in your house you plug it, they should all be properly earthed, in theory to the same place (some stake in the ground under your house probably).

TBH, I don't worry about it, I just make sure to not touch electrical bits without touching the case or PSU first.