Michael Rigby-Jones escreveu:
>   =

>> -----Original Message-----
>> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
>>     =

> Behalf
>   =

>> Of Jinx
>> Sent: 08 August 2009 00:20
>> To: Microcontroller discussion list - Public.
>> Subject: Re: [EE] Element corrosion
>>
>> My nephew the apprentice sent me this in our correspondence about
>> heater elements
>>
>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>
>>
>> I drained the cylinder, replaced the element, refilled the cylinder
>>     =

> and
>   =

>> wired in the new element.......... only to have the exact same thing
>> happen!! A little anoyed, and puzzled, I decided to put my voltage
>> testers on the incoming to see if there were any abnormalities. On
>> the isolating switch, I tested between phase and earth - 230v, phase
>> and neutral - 230v, and then...........earth and neutral - 230v dun
>>     =

> dun
>   =

>> dunnnnn. I was on to something, as there should be no potential
>> between earth and neutral as they are connected back at the Earth-
>> Neutral bars in the switchboard
>>     =

>
> Given a single phase system, I don't quite understand how there could be
> 230v between Live and Neutral at the same time as 230v between Neutral
> and Earth?
>
> Mike

I have seen places where the mains are at 127V and they connect showers
and heaters on a phase-phase circuit. So, where you should expect to
find Phase-Neutral-Ground you have indeed Phase-Phase-Ground.

This is not my area of expertise, but I know there are several possible
installation configurations (Y, delta, split-phase, etc.) Perhaps one of
them may explain this odd voltage measurements.

For instance, in a three-phase system without a fourth wire for neutral,
if you ground one of the phases (making the neutral of it), then you
could get these same results if using the two remaining phases to power
the heater.

It is probably out of the standards and possibly illegal in some places,
but in may father's farm the power grid was 3-phase 127V without neutral
and we used phase-phase to get 220V for the houses. The showers didn't
even had ground connections and never anybody got an electrical shock
while bathing.

Regards,

Isaac

__________________________________________________
Fa=E7a liga=E7=F5es para outros computadores com o novo Yahoo! Messenger =

http://br.beta.messenger.yahoo.com/ =


-- =

http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist