2391 practical

[nickjowett]

Hi
I have my 2391 practical in the morning and I am a bit confused about one thing. I have done a lot of single phase testing but very little 3 phase. I know that before you re-energise a single phase installation you check the supply polarity but do you do the same with 3 phase?If so what is the procedure? would you test between each line and between each line to Nuetral and then Earth? Would you check phase rotation at the distribution board? Any tips would be welcomed.

Thanks Nick

 

[ackbarthestar]

Yes, Phase rotation is part of the assessment. Measure at the DB and at the skt outlet. The assessment centre should provide this item of equipment for you to use.

Don't forget.......... Safe Isolation !
Test your instrument on either a known working supply or better use a proving unit.
Test for a voltage across all Live conductors then to earth and then to neutral and don't forget to test between Neutral to earth.
Lock off and apply a warning sign.
Recheck your voltage indicator.

If you don't do this you will be referred (fail)
Otherwise good luck and hope you do well.

 

[SirKit Breaker]

Yes, Phase rotation is part of the assessment. Measure at the DB and at the skt outlet. The assessment centre should provide this item of equipment for you to use.

Don't forget.......... Safe Isolation !
Test your instrument on either a known working supply or better use a proving unit.
Test for a voltage across all Live conductors then to earth and then to neutral and don't forget to test between Neutral to earth.
Lock off and apply a warning sign.
Recheck your voltage indicator.

If you don't do this you will be referred (fail)
Otherwise good luck and hope you do well.

This is a MUST and you must be provided with an Approved Voltage Tester, and a Proving unit.
You should be provided with a phase rotation indicator, if you use a MFT it will probably have that selection available.

Dont dwell on the 3 phase part too much, there are only 2 line conductors more than on single phase, so look at it as 3 single phases.

to dead test.

1 Prove voltage tester
test for dead as follows,

L1 to E
L2 to E
L3 to E
E to N
N to L1
N to L2
N to L3
L3 to L2
L3 to L1
L1 to L2

Reprove tester.

I find that this is the easiest way to dead test, and it is the method that i teach. The reason behind this is that you only move one probe at a time, and it is easy to remember the 10 tests. It doesn't matter how in which order you do the dead test, but if you miss one it is game over.

I tell my students to practice at home using a knife and fork and 5 different coins, until they can recite it to me.

Cheers..........Howard

 

[topquark]

This is a MUST and you must be provided with an Approved Voltage Tester, and a Proving unit.
You should be provided with a phase rotation indicator, if you use a MFT it will probably have that selection available.

Dont dwell on the 3 phase part too much, there are only 2 line conductors more than on single phase, so look at it as 3 single phases.

to dead test.

1 Prove voltage tester
test for dead as follows,

L1 to E
L2 to E
L3 to E
E to N
N to L1
N to L2
N to L3
L3 to L2
L3 to L1
L1 to L2

Reprove tester.

I find that this is the easiest way to dead test, and it is the method that i teach. The reason behind this is that you only move one probe at a time, and it is easy to remember the 10 tests. It doesn't matter how in which order you do the dead test, but if you miss one it is game over.

I tell my students to practice at home using a knife and fork and 5 different coins, until they can recite it to me.

Cheers..........Howard

Now all they need is a handy mneumonic to remember it

 

[nickjowett]

Thanks for the replies.
Nick

 

[fredrico]

Hello, i am doing my practical next week as well. When carrying out the test on the motor, on the test schedule, do you write down all the results for the R1+R2 readings for each phase, or just the highest?? If you do write down just the highest reading, what do you do with the other 2 rows on the test schedule, because its a 3 phase motor it will take up 3 lines on the schedule, do you put lines through them?? Cheers not done much 3 phase tesing myself. And when you say checking for phase rotation, do you mean tseting with a 3 phase rotation meter like a rotating disc type?? Or just with an approved voltage indicator??

 

[ackbarthestar]

And when you say checking for phase rotation, do you mean tseting with a 3 phase rotation meter like a rotating disc type?? Or just with an approved voltage indicator??

Either the rotating type or the neon indicator type. Your assessment centre will supply these instruments. Whatever you do..... Do not pick up the neon screwdriver, or the non-GS38 approved voltage indicator.

 

[i=p/u]

il keep that in mind sirkit breaker,

 

[i=p/u]

2391 in january

 

[fredrico]

So is the phase rotation testing done after, safe isolation, after all the dead tests, and then when you power up the installation again?? And do you check the rotation on the on the 3 phases coming out of the main switch on the 3 phase board, or the supply side of the main switch?? And when you say test at socket, do you mean the socket that is there for the apparent motor??

Cheers

 

[Deleted member 26818]

I must admit, I don't quite understand this new requirement to check phase rotation.
What are you supposed to do, if it shows as being incorrect, especially on the supply?

 

[spark 68]

I must admit, I don't quite understand this new requirement to check phase rotation.

I must admit I don't see the need for it in most cases where you have verified your various (R1+R2) for each phase, and so polarity and also Phase rotation by default, with the proviso that you have checked the rotation at the origin.

I would rather verify the rotation throughout (after checking the rotation at the origin) with a dead test, ie. continuity, rather than another live test which only shows the phase sequence and not the possibility that all three lines could have been swapped over.

 

[topquark]

I think it's just looking for the understanding that there is a sequence to the phases and that you know how to identify which sequence they are in currently.

 

[ackbarthestar]

So is the phase rotation testing done after, safe isolation, after all the dead tests, and then when you power up the installation again?? And do you check the rotation on the on the 3 phases coming out of the main switch on the 3 phase board, or the supply side of the main switch?? And when you say test at socket, do you mean the socket that is there for the apparent motor??

Cheers

In 2391 assessment Safe Isolation, Dead Testing and then Live Testing. However, when I used to assess 2391 candidates, I used to leave it up to the candidates how they ordered their test sequence... to a limit.

The two important criteria are safety and thoroughness.

If a candidate could show that making a preliminary assessment of the external characteristics by the use of live testing, before any dead testing took place demonstrated that the supply was in good condition and within specified limits, this would help in determining that the Zs values, by either calculation or measurement, were within the time constraints and maximum impedances of tables 41.1 and 41.3, respectively.

Phase rotation can be done at either end of the assessment, but better to do it at the end to verify that not only is the phase rotation is correct but also that you have connected up correctly before you finish. Phase connections should be checked at each point of termination - Its a good job that 2391 does not include a Star-Delta motor starter ! :whatchutalkingabout

 

[Knobhead]

Phase rotation is a black art.
I served my time on a works that in the 1930’s built it’s own power station, in the late 40’s it was connected to the grid. We were running reverse to the grid. The simple solution was to reverse the grid connection and everything was hunky-dory. Come the mid 60’s new plants were built and some genius came up with the idea that the phase rotation should be corrected. Fine so long as the new plants remained isolated units. But as time went on like a spiders web the distribution systems grew to the extent they overlapped. Now think of the confusion. I built a new switch room with supplies from old and new plants, my brain went out to lunch!

The crux of the matter is it doesn’t mater what your meter says so long as the phase rotation remains constant throughout the system.

For information, if a motor is connected RYB to ABC it will run clockwise looking at the shaft. (In theory)
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