Re: Oscilloscope to view mains power

On Sun, 06 Nov 2005 06:45:36 GMT, "RR"
<newspaper.20.broom@xxxxxxxxxxxxxxx> wrote:

>I read elsewhere that if I don't care too much about accurate voltage
>measurements, I can just connect the probe tip to neutral or active and not
>bother about connecting the probe shield.
>
>The scope will then show the PD between the probe tip and the internal scope
>ground (which should be the same as the power points ground since they'll be
>on the same house power circuit - except when I'm measuring the inverter).
>
>No circuit between the probe tip and its shield would seem to be safer, on
>the face of it.
>
>Does that make sense?

If I wanted to scope mains, I'd not just poke the probes into a handy
receptacle.

If you do everything correctly, you'll just see some rather boring,
noisy sine waves; if you do something wrong then there's the potential
(no pun intended) that, if you survived, you would be wearing the
remains of the o'scope.

Build a test rig with a properly polarized mains plug, in-line fuses,
current limiting resistors, and with shielded and polarized test points.
If it's for a semi-permanent test rig (e.g., an inverter) then build the
fuses, resistors, etc. into it.

BTW, your premise wiring is most likely anti-phase rather than 3-phase
and comes from a single, center-tapped transformer that itself is across
one of the three phases coming out of your substation.

--
Rich Webb Norfolk, VA
.

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