On a sunny day (Sun, 1 Jul 2018 22:26:34 +0100) it happened Peter Percival
 wrote in :

>Theo wrote:
>> Peter Percival  wrote:
>>> Also (sorry if I'm boring anyone by returning to the subject) should the
>>> soldering iron be powered via an isolating transformer, or is it ok if
>>> it plugs straight into the mains?
>>
>> Generally there's no reason to use an isolating transformer.  If you're
>> working on live equipment it might make sense to have both the equipment and
>> iron on the isolation, but it is simpler just to unplug the equipment.
>>
>> If your soldering iron has any mains leakage that an isolating transformer
>> would protect you from, there's something seriously wrong with it.
>
>My concern is protecting the devices I'm soldering!
>
>>
>> Theo

Some practical tips, well the procedure *I* always follow with any 'tronix:
Say if you want to solder on a raspberry, and with a soldering station with
isolation transformer:
1) disconnect ALL wires to the raspi, also to the USB power.
   the AC adaptor / wallwarts have small capacitors to both mains leads
(required against interference by law)
   that put effectively half the mains voltage (so 120V in Europe) on the
connector,
   it is extremely low current (Cs are about 1.5 nF or there about), but will
kill sensitive components.
2) make sure you are free from earth
3) touch the metal of the analog video output on the raspi
   now you are both at the same potential.
4) get your soldering thing and make sure you touch it too (ground connector if
it has one [1]).
   repeat 3 and 4 if think it is needed.
5) open the raspi
6) do the soldering thing with decent solder, no acid flux, 60/40 resin core
works, or some other stuff silver based,
   USE THE RIGHT TEMPERATURE for the solder you use (requires adjustable
soldering iron, a MUST).

7) It may help to wear a tinfoil hat, but keep it cool.

FYI I have not blown up even the most sensitive MOSFETS ever.

And as an aside, (mostly for the continent) use grounded PCs, equipment, even
my lab supply is grounded,
IIRC the English have nice mains plugs with a huge ground pin, here on the
continent, lots of 2 pin stuff.
For reasons mentioned in (1) keep that half mains away from any connectors (PCs
etc have the same decoupling caps, called mains filter.
Taking these rules not seriously will get you into trouble.
Best advice I can give.

[1] not the hot side, could not resist...

To break the rules, my scope is not grounded, so I can single channel measure
stuff that carriers some voltage..
Understand the circuits and things you work on, else do not touch it.
Understand what electrons like to do.
That is the gist of it.
Start there.

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