Al,
AFAIK, you are correct - the large value resistor is primarily there to
protect the person wearing the wrist strap.
However, I do not like to do any electronic or electrical work on a
directly grounded and conductive surface - period. IMHO, there is too
much of a chance to create a short to ground with an open lead or an
accidentally placed tool in contact with a conductive work surface.
Even though we usually do not work on high voltage equipment frequently
anymore (which is where those practices originated), it is still good
practice since low voltage power (in particular batteries) can produce a
lot of damage from high current levels - I have seen several cases of
molten metal flying around as a result of a shorted low voltage/high
current source. Think about it a bit - there is a good (and similar)
reason for the instruction to ALWAYS remove the grounded lead from an
automotive battery first (even if it seems non-intuitive at first) - if
one terminal is left grounded, the tool removing the 'hot' terminal can
short to the chassis and cause much harm and injury. Don't think that
small batteries are harmless either - I once observed a 12 volt pack of
AA sized NiCAD batteries melt wire and burst when subjected to a direct
short - it was a destructive test in a controlled lab environment, but
it convinced me that such things are not harmless.
73,
Don W3FPR
[EMAIL PROTECTED] wrote:
Sorry if I missed something here, and I'm not trying to confuse issues. But,
after 40 years in the industry working with the most sensitive of
semiconductor devices, the only requirement for a series resistance that I've seen used
is in the devices like a wrist strap that were attached to the operators
body. The purpose being to protect them from possible contact with power systems
that could place the operator in the HV ground path. The 500K or larger
resistor was usually adequate to provide a non-lethal warning of somethin amiss.
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