[Elecraft] (OT) Grounding Mat

[Don Wilhelm]

Lew and all,

I would be *very* uncomfortable with a fully conducting sheet of metal 
on the top of my workbench - I even consider it dangerous.  If I were to 
touch that surface with one part of my body and accidentally touch a 
source of voltage with another part, current will flow through my body.  
Just how dangerous that is depends on the voltage - but current can maim 
and kill too (see below).
A fully conductive workbench surface negates the user protection that is 
offered by the 1 megohm resistance in a wrist strap.  That 1 megohm 
resistor is there to limit the current if one contacts a high voltage 
source, but still will be effective for dissipating a static charge.

The mat should be sufficiently conductive to bleed off static, but not a 
zero resistance conductor.  In other words, the mat should be "static 
dissipating", but not a fully conducting surface.  Just because we are 
working with low voltage supplies does not make it safe.  A short on a 
high current capacity power supply or a battery (they have LOTS of 
stored energy) can and will cause BIG sparks and flying molten metal.
A proper ati-static mat will bleed of a voltage source slowly and poses 
no danger.

Yes, the anti-static mat should be connected to ground - but there is no 
need to go overboard on the grounding thing.  A connection to the 
grounding conductor (green wire ground) of the power distribution system 
is more than adequate.  You should of course determine that the green 
wire ground is actually intact.  One of the inexpensive AC receptacle 
testers will tell you whether or not it is connected properly.

Yes, those who have stated that the important thing is to keep 
everything at the same potential are entirely correct.  Take ICs out of 
the anti-static wrapping and place them directly on the anti-static mat, 
then touch the mat before picking that part up - if you are using a tool 
to pick it up, place the tool in contact with the mat before touching 
the part.  It is just common sense - give the static a chance to drain 
off before touching sensitive parts.

73,
Don W3FPR


Lew Phelps K6LMP wrote:
> For myself, since I had it handy, I use a large sheet of copper that is connected by copper braid to the ground bus in my shack --a 2" diameter copper pipe, about 3 feet long, which in turn is connected by 4/0 cable to a series of copper stakes driven six feet into the ground, and also tied (at the far end from the shack) to the ground wire on the household distribution panel. (NOT to the white wire or neutral side of the electrical lines -- to the heavy wire that connects the breaker box to actual "earth" ground. At a very minimum the mat should be connected either to a metal cold water pipe that is known to provide a good ground, or to the "green wire" on an electrical outlet, or to a station ground as I described.
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