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From: no.top.post on 9 Jan 2010 23:08
In article <4b462ad0$0$280$14726298(a)news.sunsite.dk>, ArameFarpado <a-farpado.spam(a)netcabo.pt> wrote:

> Em Quinta 07 Janeiro 2010 08:27, no.top.post(a)gmail.com escreveu:
>
> > In article <4b44e3c5$0$275$14726298(a)news.sunsite.dk>, ArameFarpado
> > <a-farpado.spam(a)netcabo.pt> wrote:
> >
> >> Em Quarta 06 Janeiro 2010 17:23, no.top.post(a)gmail.com escreveu:
> >> > But I can't understand since the UPS is designed to switch on AFTER
> >> > the mains failure.
> >>
> >> wrong.
> >
> > OK, I don't want to influence original contributions, by giving my
> > full present analysis. But the failure process takes a finite time.
> > And I insist that the UPS can only acts AFTER the beginning of the
> > mains 'failure process'.
> >
> > Can you contribute more than "wrong" ?
>
> You are confusing a UPS with a emergency electric generator; those are the
> ones that start working after the power goes off.
> A UPS needs to keep the power up without letting it go down even for a split
> second.
>
Let's be more scientific: at 50 Hz, there are zero-crossings every 10 ms.

> The only switch a ups does when the power goes off is that it stops charging
> the batteries. The output of a UPS is allways given by the same circuits
> regardless if the power is on or off
>
> with power on:
>
> main power -> AC-DC converter -> DC-AC converter -> output
> -> charge batteries.
>
> with power off:
>
> batteries -> DC-AC converter -> output
>
> this is the only way that an ups can keep the output on without any breaks.

So the computer is fed from the UPS *always*,
and the "switch over is only from (accum to ) or (mains to D2A) ?

M-A2D-D2A->C
----B-D2A->C

>
> so resuming: if the ups's output is given the wrong voltage, frequency,
> sinosoidal wave, etc... you have two choices:
> 1- repair the ups
> 2- replace the ups.
>
What did I write to suggest that "the ups's output is given the wrong" output ?
How would that cause the earth-leakage to activate ?
============
philo wrote:
> So the conclusion is reversed from what has happened
>
> It was a ground fault which *caused* the power interruption.
>
> The UPS simply was on because the "mains" breaker had tripped

No it's a chain of events over a few milliseconds.
The UPS detects that the mains is 'abnormal' and switches;
which causes an earth-leakage abnormality.
My problem is that since the earth-leakage AFAIK is mechanical,
it should not react to the spike caused by the UPS.

What are typical earth leakage response times?
=============
> if you have electrical questions, it's better to put them in
> sci.electronics.basics
yes, the boys here are just guessing.

>i can tell you that if you desconnect the earth, ther will be no more a
>neutral in the output, you will have two live lines with a voltage
>between them, and that could cause other issues.

Yes disabling the earth-leakage-detector is not good.
==========
> > so resuming: if the ups's output is given the wrong voltage, frequency,
> > sinosoidal wave, etc... you have two choices: 1- repair the ups
> > 2- replace the ups.

david wrote:-
> This is only true with a double-conversion type UPS, which most cheap PC-
> type UPS's are not. Most cheap UPSs have a transfer switch in them, so
> the power is actually interrupted for a few milliseconds when the mains
> fail.
>
Yes, I'd expect the computer PSU to 'hold over' for 2 cycles: 20 ms.

It seems that none of you are considering the interaction back to the
earth-leakage ?

== Thanks for any reasoned answers [not guesses].
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