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

In article ,
Phil Allison wrote:

In the world of live music, I have come mixed class I / II systems that
are very scary.

In UK TV studios etc, before the days of RCDs etc, every single item of
unknown equipment - like say a guitar amp etc supplied by a musician - was
fed via a mains isolation transformer. Expensive and time consuming but
very necessary.

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.

d