Ground loops and star wiring was Re: power supply

Hello,

Ground has two purposes: Providing a "reference" for the voltage, and
providing a "safe" return path for electrons.

So I will call the first "signal" ground, and the second "safety"
ground(earth). To provide the necessary safety, they must be
connected.

BUT, they "should" only be connected at ONE point, or all sorts of
problems can occur. This group of problems falls under the heading
of "ground loops". This happens because all wires (above absolute
zero<G>) have resistance and inductance. What this means is that if
you connect these two types of "ground" "here and there", these
resistances and inductances will ensure that unwanted voltage is
present in varying degrees at various parts of the system. These
varying "unwanted" voltages are called ground loops. (because your
connections have made a path -a loop- for electrons to travel, when
they are "supposed" to only be "going" one direction...

The "one-point" grounding (called "star" wiring) minimises this. This
is why stepper drivers are all fed INDEPENDANTLY from the power
supply, and not "daisy-chained". (you see the same thing with your
drive connectors in your PC) So, first you bring all the SIGNAL
grounds (of each voltage) to a SINGLE point. This kinda looks like a
star, the wires radiate out from this central point to the various
devices at that voltage. Next you bring all these "starred" SIGNAL
grounds to a SINGLE point. Now you do the same thing with
your "safety" grounds. And FINALLY, you connect the signal and safety
grounds together at one point.

This is the ideal situation, and sometimes you simply cannot do it
(multiple enclosures), but the closer you can keep to this "ideal",
the better.

Hope this helps.

Ballendo

P.S. While we're here, the "shields" of cables should only be
connected to ground at ONE end, preferably closest to the power
supply. Again not always possible, but try.

P.P.S. There are more than a few electrical devices "out there" that
DON'T connect signal ground and safety ground. In these cases, other
means have been used to provide the needed safety.

--- In CAD_CAM_EDM_DRO@y..., "Bob Campbell" <bob@c...> wrote:
> I just built a power supply and I connected the negative side of
the power
> supply to the same ground as the green wire on my ac input line.
The green
> wire should be an earth ground.
>
> Bob Campbell
>
> ----- Original Message -----
> From: "cncforum" <cncforum@y...>
> To: <CAD_CAM_EDM_DRO@y...>
> Sent: Sunday, February 03, 2002 4:26 AM
> Subject: [CAD_CAM_EDM_DRO] power supply
>
>
> > Hi all,
> >
> > Does the ground leg of the DC output of the bridge rectifier in an
> > unregulated power supply need to be connected to earth?
> >
> > I have seen one schematic where the power supply is earthed.
> >
> > Thanks
> >
> >
> >
> >
> >
> >
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