"Tough Guy no. 1265" wrote in message
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On Sat, 07 Nov 2015 20:05:02 -0000, Fredxxx wrote:

On 07/11/2015 19:07, Tough Guy no. 1265 wrote:
On Sat, 07 Nov 2015 18:14:59 -0000, harry
wrote:

On Saturday, 7 November 2015 16:42:25 UTC, Tough Guy no. 1265 wrote:
I looked this up, I'm asking the question at the top. The replies
don't seem to be able to agree. Any sensible opinions?

http://electronics.stackexchange.com...e-mains-supply


--
It said, "Insert disk #3," but only two will fit!

It is important when electrical equipment/appliances have metal
cabinets which can be earthed. Which was everything years ago.
Without an earth, ant fault to the cabinet could not be detected and
would be dangerous if there were other earth faults.
Also get over certain capacitance effects.

Two faults is unlikely. One fault would of course not shock you at
all. Most shocks are an exposed live to an earth, isolating the mains
would remove that possibility altogether, and not change the amount of
shocks between live and neutral.

I would agree with you, but only if you can automatically detect each of
the faults and interrupt the power accordingly.

An isolation transformer might well hide some faults as well as
introducing some more and so be more dangerous in reality than the
conventional single phase supply.

But the two faults would have to be within reach of each other, eg your
washing machine and your fridge both having a fault with the opposite
conductor, and you touch both. So very unlikely.

Not as unlikely with a couple of small appliances in the kitchen.

Besides, I've never actually observed a fault where the chassis becomes
live.

Doesn't matter what you have observed, the design
of the system has to allow for that situation.

The only shocks I've ever had were worn cables on a mower, touching a
switch with wet hands when outside, etc.

A wire does come adrift inside an appliance quite a bit.

Now if the supply had been isolated, I wouldn't have received a shock.

But at the very high cost of a transformer for the entire house.

No thanks, RCDs and double insulated appliances makes a lot more sense.