wrote:

On Thursday, 3 January 2019 11:22:40 UTC, Roger Hayter wrote:
Brian Gaff wrote:

Hi, In the past in a shed I used to work on equipment with a live
chassis by having it on the other side of an isolating transformer and
earthing the non live side, if you get my drift. After all this is
just what replacing an auto transformer would do to mains gear of that
age. However I used to fly by the seat of my pants in those days, and
so what
I'd want to do with my new shed when its built is also to protect that
circuit with more than a 5 amp fuse.

Now I'm probably well outside of the law here on this one but two
problems come to mind. First what sort of breaker and also of course
you would need any gear connected to have a plug on it that could not,
accidentally be put into a standard socket as that would be disaster
on many levels. are there special plugs or sockets for this kind of
use?

Brian

I used to do the same, but I haven't seen any live chassis equipment I
wanted to repair for about fifty years. And getting the series heater
replacement valves might prove expensive.

under an hour's pay each

Fascinated to know you can still get them. Though I know some LOP
valves are still in use.



Having said that, I can't think of any way an isolated supply with one
side connected to local earth could be protected in any way that doesn't
make it more hazardous to the operator rather than less.

RCD after the iso transformer.

That only works if you reference the secondary voltage to earth before
the RCD. Otherwise there is nowhere for unbalanced leakage to go. And
I am not sure that is actually safer, as it does not protect against a
shock from live to chassis, the most dangerous kind.





NT


--

Roger Hayter