On Sun, 14 Nov 2004 00:35:06 GMT, "Mark Jerde"
wrote:

What are the specs for a
resistor to put between the DC grounding system and the water pipe to limit
the current flow yet allow for DC static discharge?

They're complicated. It's a few megohms (9M from memory) but like any
of these high value resistors, you have to account for construction
and surface paths as much as the resistor itself, and especially
guarding against failure modes that could cause a short. Usual HT
practice is to never use a single resistor anyway, but to use smaller
ones in series. If one fails short, it's just a small change in
resistance, not an overall short.

UK practice is to buy a plugtop. This fits in a standard bench power
outlet, is bright yellow and has a number of press-stud connectors on
the top. Inside is the right sort of resistor, bonding you to the
mains ground. If your bench was built for electronics work, then it
might have such connectors built in anyway. Static wrist strap

Or can someone talk me out of a fear of an open megaamp path-to-ground
throughout my shop?

For the question of "What sort of minimum resistance makes me vague
safe ?" then it's hard to answer. But a resistor of just 27 kilohms
would limit current to under 10mA, and that's going to reduce the
serious hazard massively.

NB - I'm not suggesting static straps with 27k resistors !

So I hope that shows that putting in even a relatively low resistance
to the ground path can keep the fault current non-lethal.

As a rather gruesome example, there was a recent UK case (discussed at
length in uk.d-i-y) where the daughter of a TV presenter (?) was
electrocuted in their kitchen. A metal pan rack had been installed
over the cooker and the mounting screw had nicked a cable in the wall
(the cable had been improperly routed and not correctly protected).
For some time the family had experienced a tingle from this rack, but
done nothing about it. Finally the victim was killed by it, because
one day her ankle also happened to be touching the well-earthed and
low-impedance case of the dishwasher (there was a contact burn on her
ankle aferwards).


--
Smert' spamionam