On Sun, 03 Aug 2014 16:37:01 +0000 (GMT), Jim Lesurf
wrote:

In article , Don Pearce
wrote:
On Sun, 03 Aug 2014 10:16:40 +0100, "Dave Plowman (News)"
wrote:

We now have the annual PAT test. In my lab once a year a chap comes
round and tests the integrity of the grounding of everything that has a
mains plug, from the 100 grand Network Analyser to the kettle in the
kitchen.

Once he has gone all the oscilloscopes get their grounds removed once
again so they can make floating voltage measurements and not introduce
ground loop mess into normal measurements.

It doesn't actually make anything safer, but the company lawyers like it.

Nice to see that people are maintaining the old traditions. :-)

FWIW When I used to install and use systems on the old UKIRT (Telescope)
they were always 'grounded'. But always gave you a multi-kV static shock if
you were the first to touch them after they'd been left un-touched for
about 10 mins or more. The ground connection was essentially dry rock in a
dry atmosphere. So was little more than a common reference. Certainly not a
way of ensuring no overall charge potential. 8-]

One trick was to send the newest PhD student to adjust the kit and the
watch to see if we could see the spark in the darkened dome. Usually
accompanied by a suitable noise from the student. :-) Rite of passage.

Jim

What do you reckon was the capacitance to true ground? More than a
couple of hundred pF and you can start to feel it properly.

d