Simple ESD mat and wrist wrap setup

I have a hard time finding a how-to.

I would like to set up a simple ESD mat and wrist wrap, but I am not sure about is the the 1 MOhm resistor should be, if at all.

Several options:

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  1 MOhm from ground outlet to the mat, wire from the common earthing on the mat to the wrist wrap.

  
  


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  1 MOhm from ground outlet to the mat, wire from another contact on the mat to the wrist wrap.

  
  
  


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  1 MOhm from ground outlet to the mat, 1 MOhm from the same mat contact to the wrist wrap.

  
  


• 
  

  wire from ground outlet to the mat, 1 MOhm from the same mat contact to the wrist wrap.

  
  


• 
  

  wire from ground outlet to the mat, wire from another mat contact to the wrist wrap.

  
  

I am not sure why the 1 MOhm wire is needed since the mat itself already has that kind of resistance (as long as the wrist wrap does not connect to ground directly, but through the mat).

Which solutions above are ok? Which is best? Should I do something else instead?

Answer

It doesn't matter, as long as some resistance is there.

The resistor limits the current from the discharge to something that won't damage the device. The actual value of the resistor is mostly arbitrary, it should be large enough to properly limit the current from even an 1 kV difference, and small enough to eventually allow the potential to even out within a sensible timeframe.

Whether it's 500 kOhm, 1 MOhm or 2 MOhm is not that important, so use whatever is most convenient for you, ideally a configuration where the wire from the wristband doesn't catch on the soldering iron all the time.

I'm using a grounded ESD chair, which is even more convenient, but I've also seen ESD sandals and grounded floor plates.