In article ,
Phil Allison wrote:
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.

** Really ????

Yes really.

Bet the Beeb et alia stopped doing that when they nearly electrocuted
the first guitarist.

Sigh.

1. The most common error in AC plug wiring is Neutral-Earth reverse -
the item works and there is no big problem until you find an AC outlet
that has Active and Neutral reversed.

Then that device would simply not work.

2. Add a 240:240V iso-transformer that carries the supply ground
through to the outlet and it becomes instantly lethal. Draw it out on
paper if you doubt me.

That's why they didn't.
FYI:

Supply earth goes direct to one side of the amp's AC tranny, then the
iso-tranny's 240V winding and back to the amp's chassis. The amp will
not run - but the chassis is 240AC live.

There is no 'live' and 'neutral' on the output of an isolating transformer.

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*Warning: Dates in Calendar are closer than they appear.

Dave Plowman London SW
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