A purely rhetorical question?

[Knobhead]

Phase rotation. I’ve noticed a few MFT meters showing this as a feature, but for what use in either domestic or industrial?

It’s a totally pointless test!

If you have two incoming supplies you don’t check rotation you check phase to phase voltage:

R to R = 0V
R to Y = 433V
Y to Y = 0V
Y to B = 433V
B to B =0V
B to R = 433V

All would be OK with the above readings

 

[snowhead]

As it's titled Rhetorical I don't need to answer,,
But there is a need for rotation checking where a 3ph supply exists.

Conformation on a new / updated install that rotation follows L1 L2 L3 at all DB's.

More appropriate to situations I deal with, when connecting a whole site temporary generator following loss of external DNO supply due to the pikey effect or loss of site 11kv TX or main switch gear, conformation that the temp supply is correct rotation before transfer.
All our sites are always internally L1 L2 L3 correct.

 

[Knobhead]

I’ve worked on sites with over 70 11KV transformers and never used a phase rotation tester yet. I did the tests listed above.

 

[spark 68]

I would partially disagree that it is a pointless test.

This test really only needs to be carried out at the incoming supply to verify the rotation, either CW or CCW (most if not all of the installs I have done are CW), and is supposed to be checked at other sub boards to make sure the sequence is maintained throughout.

I have always argued that the sequence can be checked during polarity testing (a dead test) and R1+R2 testing, as by default the sequence would be correct if the continuity tests are correct, and the new GN3 elaborates further in this respect.

I can see a situation where it is impossible to do dead testing for whatever reason, and I would agree with Tony it is possible, and probably the best way, if possible, to measure the volts phase to phase and Neutral to Neutral against another known source to check the sequence is maintained, the rotation test itself would not show if this was correctly wired, as the rotation test itself does not identify the phases, only the sequence.
for instance you could have L1,L2,L3 at the source giving CW rotation, and L2,L3,L1 at a sub board, mis-wired but still giving CW rotation.

The rotation test may also be of use on pure 3 phase motor circuits, where you are faced with three un-identified (same colour etc.) conductors, say at an isolator, and you need to know which way the rotation is, especially if the motor is in an inaccessible, or in difficult to access position, or maybe where reverse rotation could be dangerous or cause damage.

So I would say, it is of limited use in certain applications, and horses for courses, provided you understand the limitations of this type of test.

 

[Guitarist]

During my apprenticeship in industry, we would use a phase rotation tester as a quick check on sockets after replacement/repair/installation to ensure that they were all the same throughout the site. This was due to the fact that we had some plug-in equipment which destroyed itself if it ran backwards

 

[Knobhead]

During my apprenticeship in industry, we would use a phase rotation tester as a quick check on sockets after replacement/repair/installation to ensure that they were all the same throughout the site. This was due to the fact that we had some plug-in equipment which destroyed itself if it ran backwards

Yes I agree with the socket outlet argument and it is a good point I hadn’t considered.

Thank you.

 

[plugsandsparks]

Hi Tony, only really used mine in anger when i was moving a load of CNCs and Lathes and wanted to minimise their disruption and my embarassment if i offered them a new supply that ran backwards.
All i did was measure the phase rotation before the M/c was disconnected and made sure it was the same when i reconnected, indeed they were often different and not related to any L1,L2,L3 or U1,V1,W1 labelled inside the m/c.
Also when i was doing a EICR i noticed that one sub board was running backwards, it was not painful to redo the incoming cables and change the final ccts to get it all back to sequence.

 

[JD6400]

We have several MFT's and multi meters that have this function and to be honest I tend not to use them unless on a new supply .
I always prefer to label well before replacing any old boards and then find a piece of equipment that will not be damaged if started in reversing just in case I have made a mistake , or just de-belt a compressor or the likes .
I know the meter should not lie but i just prefer to do it visually as i trust my eyes more than a meter , plus the fact if it was arse about face before i started it will be again , with out the fear of recking any kit that is already configured so .

 

[Darkwood]

I had a supply upgrade on an industrial site and the DNO brought a larger supply cable in joint of main street, they had connected it CCW as oppose the CW which was the previous supply rotation, all the machine are wired and connected in existing and some would have been damaged if rotation wrong, i asked DNO why they had reversed from previous rotation and was told it was the only way they could make the joint kit off in the road as the cables layers had lad the cable in the opposite way round.
Had i not checked this it would have been costly in repairs but solution was to wire busbar chamber to change it back over and mark up accordingly.

I dont see the need in domestic though.

 

[Engineer54]

Can't tell you how many times a hospitals supply rotation in Jeddah had been reversed, as and when the electrical supplier brought more and more of the local area on line. this was mainly on the MV side of things After the second or third time, i inhibited the stand-by Genny from changing over back to utility supply, unless phase rotation was correct, (initial system didn't include the appropriate phase rotation protection relay). Main supply tails needed swapping at least a couple of dozen times or more in that 2 year period!! lol!!

 

[jefferslot]

phase testers are handy if one is not sure that L1 is actually L1 and you need to know direction of rotation. but you are correct - voltage comparison is essential for connecting two three phase supplies together.
when connecting two live 3 phase supplies together, phase rotation checks can be miss leading because phase sequence must be identical as well as phase rotation
eg A) L1 L2 L3 rotation clockwise : B) L1 L3 L2 rotation anti clockwise : c) L3 L1 L2 clockwise : D) L3 L2 L1 anticlockwise
notice A) & C) both rotate clockwise but are out of sequence and so is B) & D) but both rotate anti clockwise

 

[Engineer54]

phase testers are handy if one is not sure that L1 is actually L1 and you need to know direction of rotation. but you are correct - voltage comparison is essential for connecting two three phase supplies together.
when connecting two live 3 phase supplies together, phase rotation checks can be miss leading because phase sequence must be identical as well as phase rotation
eg A) L1 L2 L3 rotation clockwise : B) L1 L3 L2 rotation anti clockwise : c) L3 L1 L2 clockwise : D) L3 L2 L1 anticlockwise
notice A) & C) both rotate clockwise but are out of sequence and so is B) & D) but both rotate anti clockwise

Very few phase rotation/sequence testers will indicate true LI, L2, L3, and certainly not any on that are included in MFT's. Those testers that will, cost in excess of 3 times that of the normal phase rotation testers... Mine does, it's a Yank made tester and if i stop trying to remember the name of the manufacturer, i might actually remember it!! lol!!

 

[Knobhead]

What gives it’s reference to 0° rotation? It’s imposible!

If I’m phasing out transformers I can RYB rotation check transformer 1 as the base reference. No. 2 will be checked R>R Y>Y and B>B all should be 0V. OK to close the bus section switch if I needs be. But without those checks forget it! Phase rotation is one thing, phase alignment is another!
I’ve fallen foul of this before! Transformers 1 &2 DYn11, transformer 3 DYn1.
60° out of phase to each other, can you imagine the outcome of closing that BS switch!
I’d be sat on a cloud playing my harp!

 

[Engineer54]

Well it's certainly not impossible Tony, as mine which is an industrial model and other up-market phase sequence testers can do just that!! Mine also has an override memory, that can be set-up at say the main intake where the sequence can be coming in as L1,Red L3,Yellow L2,Blue. (just an example) I can then go to any panel or motor etc, and check that the same sequence has been maintained throughout the installation.

As i say these units are expensive, cheapest basic unit, probably in the 200/250+ quid. Mine, like most of my other test equipment was a ''present'' (lol!!) from a happy contractor ...

 

[Knobhead]

The works I served my time on had it’s own power station. When came the time to connect to the grid, we were going backwards!
Then came this new weird thing 440V, everything had been 550V before. In a fit of shear madness my cousin the then works engineer decided all new plants should be the correct phase rotation.
So my first major project. The plant had a 2MVA 550V supply, I had to put in 3MVA at 440V, which rotation do we go for! Because it was going to be along side the old system we went for reverse. It was bloody chaos, as plant’s grew they tended to overlap. 440V from plant 1 was opposite rotation to 440V from plant 2. Not to much of a problem until muggings here was asked to install a feeder pillar where supplies could be swapped about to feed a small plant. Trying to do knitting with 185mm 3½core isn’t my idea of fun!
In some switch rooms I had the gear re-sprayed different colours to show the voltage and rotation. The feeder pillar looked a bit strange, it was mainly blue but with a yellow incomer switch at one end.

The gear was coloured:
Grey, 550V CW
Blue, 440V CW
Yellow 440V CCW