On Sat, 07 Nov 2015 21:52:56 -0000, Rod Speed wrote:



"Tough Guy no. 1265" wrote in message
news
On Sat, 07 Nov 2015 20:33:48 -0000, Rod Speed
wrote:



"Tough Guy no. 1265" wrote in message
news 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.

I have never had ONE appliance get live on its chassis,

It happens anyway.

Not as often as other problems.

nevermind two.

You don't need two, in fact two would be safe. The problem is with
one with a live case and all the others with an earthed case and other
earthed stuff like the sink etc.

No, because with isolation you don't have earths everywhere. You'd have to therefore have two faults, one with live to chassis and one with neutral to chassis.

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.

Why allow for a remote possibility, thereby creating a very likely one of
live to the ground?

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.

No,

Yep.

because they are inside and don't get touched.

They touch the case and that is a problem.

They come adrift when the wire comes out of what its
supposed to be attached to and when cord anchor isn't
good enough and some fool lets it fall off the bench
and hang on the cord etc.

Usually the cord then yanks out the other conductors and live and neutral short, blowing the fuse.

--
What's the difference between PMS and Mad Cow Disease?
The number of tits.