Transformer question (only slightly OT)

[Tony Duell]

> 
> On 9/3/2006 at 11:54 PM ard at p850ug1.demon.co.uk wrote:
> 
> >No, I'm not afraid of the mains, but I do treat it with respsect.
> 
> Especially when your mains voltage is twice that of the US and Canada.  Is
> the current supplied to a wall receptacle just as high?  Our 120v

Our wall socksets are rated at 13A, but are almost always wired on what 
we call a 'ring main' (a complete ring (electrically) of cable with many 
socksets connected to it), which is protected by a 30A fuse or breaker.

The mains plugs contain a cartridge fuse, values from 1A to 13A are 
available, nut only 3A and 13A (and sometimes 5A) are commonly seen.

As a result, I feel wall-warts are dangerous in the UK. They do not 
contain na internal fuse, so could in theory draw nearly 30A from the 
mains before the circuit fuse failed. The mains transformer primaty of 
the wall-wart is supposed to burn out in a safe way, my experience 
suggests this is not always the case.

I _never_ use wall-wards plugged straiht into the wall. Putting them on a 
fuesed extension lead is somwhat safer. Altough personally I prefer a 
decent transformer with fuses in both priamry and secondary circuits.

> receptacles are typically "protected" with a 15A or 20A circuit breaker.
> 
> Another thing to have on your shop outlets is GFI protection.  It could
> save your life.

It can also be a right royal pain when a main filter has enough 
unbalanced current to trip it. Ad it won't protect you if you're 
relatively well insulated from ground but manage to connect yourself 
between live and neutral or equivalent.

I use a GFI (RCCD, whatever it's called this week) in placees where there 
could be dangerous leakage (sockets for outdoor appliances, in the 
darkroom (a mixture of electrics and water, after all :-)), and so on. 
But I don't have one on my workbence, nor do I want one.

-tony