Guy's,
There have been testers around to do this sort of test, for years.
I note that a number of two probe testers give a Phase Rotation reading on them, in the form of a circular arrow on an LCD screen.
Could someone please correct my way of thinking, in so much as,I was under the impression, to effect a decent 3 Phase Rotation test, you had to have a tester that would connect to and test all 3 of the phases.
The question I ask, is this, how can a 2 probe tester do the same job as a 3 Clamp tester?

I cannot imagine a wiring configuration with only two phases that would tell a phase rotation for all three. Could you share a product manufacturer and model?
This one has three wires connected. http://www.traknet.com/wei/aemc9.html
My understanding is many rotation testers are really small induction motors that rotate in a direction relative to the phase rotation measured/applied.

Maybe an electronic meter could see phases AB, determine that they are 120 deg out of phase and assume that the third phase is either before the A or after the B, resulting in clockwise rotation either way ABC or CAB.

[This message has been edited by Ron (edited 08-13-2004).]

Hmmm..... I don't recall ever seeing a two-probe tester, but I don't get involved with 3-phase much.

Let's say you connected to two phases, A and B. There are only two basic possibilities no matter which two of the three phases you picked at random:

#1. A leads B by 120 degrees. Therefore C must lag B by 120 and lead A by 120 deg.

#2. A lags B by 120 degrees. Therefore C must lead B by 120 deg. and lag A by 120 deg.

So as I see it, you could prove rotation in this way.

However......

You would still need three connections to be able to get a reference point for A and B.

In the case of, say a British/NZ 415Y/240-volt system, we know that A and B are 240V to ground. But unless you have a third reference point, you have no way to determine which lags or leads the other with respect to ground.

Any instrument connected solely across A and B with no other point of reference will see only a simple 415V RMS sinusoidal waveform, nothing more.

A suitably sensitive device might be able to use capacitive coupling to the user's hand to obtain a ground reference. That's the only way I can think of.


[This message has been edited by pauluk (edited 08-13-2004).]

I don’t think phase sequence can be defined with less than three connections. Trumpy, do the red, cylindrical testers {forgot the brand} you spoke of use three leads for phase sequence tests?

The Ideal, Greenlee and Amprobe testers all have 3 leads... I too am cornfuzed...

Bjarney, the information about the Duspol tester, that uses 2 probes to effect a Phase-sequence test can be found at this site:
=http://www.benning.de.paus-service.de/cmsfiles/784314_duspol_gb.pdf http://www.benning.de.paus-service.de/cmsfiles/784314_duspol_gb.pdf
Edit: Bad link!

[This message has been edited by Trumpy (edited 08-18-2004).]

[This message has been edited by Trumpy (edited 08-18-2004).]

Mike,
Is this the one ?
Don

Try this link

I've seen these testers too and never understood how they work.

Mike, thanks. For the life of me I could not remember “Duspol.”
www.benning.de/alt/englisch/eduspols.pdf www.trueshopping.co.uk/product.php?...=5&pn=Draper+Duspol+S+Voltage+Tester

“…Indicates The Phase-sequence Direction of a Three-phase Main Provided The Neutral is Earthed.”

That may mean: two phases and a neutral, which is a valid phase-sequence test.

bj,
But the tester only has two leads.
Don

 
Don, I’m stumped. I can’t find an online manual for the Duspol S {or Digital} that details the feature. www.benning.de/alt/englisch/pruef1.htm

The Knopp K3 “pillbox motor” has supposedly been around since the 1920s. It will operate with less torque on a ‘network’ connection [2ø+N] compared to 3ø. www.knoppinc.com/Specifications/Leaflet%20No%20427%20K-3%20Instructions%20Rev%20E. pdf




[This message has been edited by Bjarney (edited 08-18-2004).]

Guys,
Sorry about that little spat with the computer above.
I was trying to type the URL of a PDF file that gives a catalouge for the complete range of Duspol voltage indicators.
I tried to enter it 5-6 times and everytime an error of some kind!.
Thanks a bunch for your help guys, in locating that link.
Bjarney,
The link that C-H gave above is the one that starts the download of a PDF brochure from Benning, who manufacture the Duspol.
It gives specs on each tester too.

{Edited to add last bit.}

[This message has been edited by Trumpy (edited 08-21-2004).]

I think that supports the possibility of capacitive coupling via the user as the third "connection" point.

My bet is that if you opened up one of these units you'd find a plate of some sort inside the handle to achieve this coupling.