[sdiy] Leaking line filter (was: Grounding & computers)

Synthusiast synthusiast at gmx.net
Fri Dec 28 02:02:41 CET 2001

Magnus Danielson wrote:
> Jim Patchell wrote:
> Hi Folks,
> >     Yikes!
> >
> >     One posiblility is there is a line filter that the mains goes
> > Each side has a cap that goes to the chassis....this makes a voltage
> > and will give you 110v on the chassis...you really need that earth
ground to
> > prevent this.
> >
> >     Anyway, this is my guess.
> I'd go even further... I'd simply state that this is the most common
> case of getting a hot chassi. The reason why is however interesting.
> The caps are chosen to not produce too much leakage... for 117 V, but
> when you put the same filter in a 230 V system (which is what Europe
> have these days) you do sense the leakage.
> There is a simple enougth way to test this. If you have the box
> unpowered and still sense the current, then it is the filter since it
> is allways hot, regardless of the power-switch.
> Despite this, I allways recommend the usage of these filters. They do
> the rigth thing for most situations, so there is not real reason to
> avoid it.
> Also, one should if possible run with earthed contacts, there are
> other benefits with doing that.
> Cheers,
> Magnus

I was suspecting the line filter of the computer too. Now why are those caps
in the line filter directly connected to the earth ground plug? Isn't it a
little odd to leak current to the safety earth when this has nothing to do
with safety measurements? If those caps are at their max limit of leaking
it's very possible (especially in areas where you have 230V) that they set
off the earth safety switch. And if people then stop grounding their
computer to keep it from triggering the safety earth switch, they create a
very unsafe situation in their home with 110-115V on their computer case.
All because of these 2 caps in the line filter. Why?


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