Proper Grounding Techniques
jim at g1jbg.co.uk
Sat Mar 12 11:47:52 CST 2005
> Roger Merchberger wrote:
> > Dontcha just need to put a 1MegOhm resistor between the "Grounding
> > Station" (i.e. foil) and the earth ground connection?
> Come to think of it you do. How ever in my case the only time I'll be
> using a ground for static
> electricity control is when I'll be inserting the chips and that will be
> with power off. Now modern
The idea of the 1M resistor (actually, there should be two 1M resistors in
series, in case one fails), is to protect the engineer from shock IN BOTH
DIRECTIONS, not only touching live parts within the equipment, but also if
you come between a "floating" earth (Earth conductor in the UK can be
several 10s of volts - I've measured it as high as 80V above true earth) and
I can recomend the 3M products. These are a dissipative type mat, which has
a conductive layer between two insulating ones, and discharges static by a
capacitive method, the usual wrist straps, and commoning blocks. They also
produce a field service kit, consisting of a wrist strap, dissipative mat
(with pockets - it will double as an ESD bag), and a grounding point which
plugs into a standard mains outlet. The grounding unit has a self test
facility for both the ground and the wrist strap.
Dissipative mats are better, as you can place a board containing a backup
battery on them, without worrying about shorting it out!
There are also various mat and starp testing products, but for most of us,
these would be a luxury.
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