Proper Grounding Techniques

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 true ground. 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. Jim.