ESD – Is Plugging ESD Strap to Wall Ground a Bad Idea?


I have gone through this answer on Superuser, while it provides good information, I still have a specific question from electrical/electronics engineering point of view.

Is it wrong and unsafe to connect the other end of the ESD wrist strap to the ground point on the wall socket?

What harm can it do and if it’s wrong, why?

I was watching a Youtube video about assembling computers by a user who seems to be a professional and he says he has been in the business for over 2 decades.

The video discourages connecting ESD strap to wall socket ground, it also says that when you connect ESD strap to metallic part of cabinet, remove the power plug from the PSU. However except a reasoning that you could get electrocuted with such a setup, no further technical explanation is given.

I have worked in an IT company that was TL9000 quality certified. This standard demands ESD protection deployment wherever necessary. All relevant test benches there had ESD mats connected to common ground. All terminals had a point to plug the ESD strap’s other end and all those were connected to ground and eventually going to the earth pit. So discouraging ESD strap connection to wall socket ground (that ultimately goes into the Earth pit) is a totally new concept to me.

Best Answer

If your ground strap has a proper current limiting resistor, then you would be perfectly fine connecting it directly to ground.

If your ground strap does not have a resistor, then it greatly increases your chances of dying if you connect it directly to ground. If you don't have a resistor in your ground strap, and you touch a live wire while wearing your ground strap, then you will get full line voltage and current applied to your body - and you won't be able to break the ground connection.

Ground straps are there to drain and prevent a build up of static charge. You don't need a fast discharge.

A ground strap should have a certain resistance (usually 1 megohm or more.) That drains any charge on your body, but limits the current in the event you accidentally touch a live wire.

A 1 megohm resistance will drain the charge on your body quickly enough - your body's capacitance is only some few 10s of picofarads. If you were charged to 10000 V (can easily happen) then it would take less than 1millisecond to discharge your body through a 1 megohm resistor. Fast enough.

If you are grounded through a 1 megohm resistor, and touch a live wire (say, 220V ac) then a maximum current of 0.2 milliamperes will flow through your body. It might tingle if you are exceptionally sensitive, but it won't injure or kill you.