2391 Testing and Inspection practical.

[dangerousdave]

Hey guy's i'm studying my 2391 testing and inspection and have the practical next week. Before anyone say's i have used sparky heaven which has been very useful but mainly in perparing for the theory side of things. As has the college course i've been on, there has been no practical training. Through the nature of my work at the moment i have only been able to gain limited hands on expirience unfortunatley. Is there any advice anyone can give me please for the practical?

Cheers.

 

[ricicle]

You need to be confident of what you are doing especially on the full inspection and test.Show the assessor that you know what you are doing and the reasons for doing it.You will need to work at a good pace to complete in time so make sure you get stuck straight in. If you have time do a practise session somewhere.

As for the fault board they are fairly obvious to any good spark, just note down everything you see.It doesn't matter if you get more as long as you get the ones they are looking for.

And don't forget all the obvious things like checking the tester before and after testing, not just on isolation tests but that the tester is zeroed for R1 + R2 tests etc etc

Good luck.

 

[dangerousdave]

Thanks ricicle. I'm pretty confident about the individual tests, obviously in getting (R1 + R2) in doing seperate continuity tests and the IR test. I know to take all control gear out and short any sensitive equipment out. Though because of the lack of experience i'm a little less confident in applying the Earth Fault loop impedance test.
I'm getting mixed up with that test and the Prospective short circuit current test. I have been told that there will be a 3 phase board to test which also has a sub-main DB. Will the PSCC test need to be done at the origin of the 3 phase board only OR will i need to also gain the PSCC at the sub-main DB, and will a RCD effect the results of the test??
I suppose basically will the whole (PIR) need to be two seperate lot of results, ie one for the 3phase board and one lot for the sub-main DB??

 

[ricicle]

One test sheet for 3ph board, one for single phase board.
Ze and PSC at both boards...but there will be Zs at the single ph board as well as it is a final circuit off the 3 ph board.A couple of lads on my course failed because they forgot this!!

 

[RobFurn]

You may get asked to calculate (rather than measure) the Zs of all the circuits on the single phase board i.e. Ze+ (R1+R2). make sure you read all the instrucitons before you get started.
And as Ricicle says make sure you measure the Zs of the sub main its easy to forget as the boards are on top of each other. IMO this is a bit tight of the C+G to fail people outright for this but there you go.
Just treat it as another circuit on the certificate i.e. Name it Sub Main or Top board/Bottom board.

 

[ColJack]

just so i got it straight in my head..

to test for Ze you take the incomming earth out of the MET to eliminate multiple earth paths?

Zs of the sub main would be the same test but with the incomming earth connected to the MET?


both tests would be on the live side of the isolator with it switched off?

 

[partpdoctor]

Hi coljack
it would be easier to measure the Ze, then the R1+R2 of the sub main and use this Zs as a Zdb for the top board, so you sort of move the Ze along
whatever you do switch off and prove off,,,otherwise it will be an instant fail.....most examiners will help you along if you are nervous etc but not doing the above is the kiss of death

 

[Paul Barker]

Remember to always do the tests in the correct order.

Watch out for the coil in the no volts isolator for the 3 phase motor it has to be taken out temporarily to do IR tests.

 

[Podooser]

I am doing this same practical exam tomorrow. I still find it difficukt to understand exactly how and where to measure Zs of the sub main. Can anyone help please?

 

[ricicle]

I am doing this same practical exam tomorrow. I still find it difficukt to understand exactly how and where to measure Zs of the sub main. Can anyone help please?

Zs of the sub - main is measured at the incoming terminals of the board it is feeding (with the main switch of the sub - board off) This will be noted on the EIC schedule of test results for the 3ph board as the sub - main is a circuit off that.

The Ze (or Zdb) is also measured at the incoming terminals of the sub - board with main switch off and earthing conductor disconnected.This is noted down at the top of the schedule of test results for the sub - board.

Double check with your tutors which way they prefer to see this as I was told it was acceptable for this to be noted as Ze but I have had a debate over on the IET about there only being one Ze per installation.

 

[Podooser]

Thanks for that Ricicle. So the difference is Zs of sub-main is is tested with earth connected and Ze with the incomming earth disconnected. Have I got that correct.

 

[ricicle]

Thanks for that Ricicle. So the difference is Zs of sub-main is is tested with earth connected and Ze with the incomming earth disconnected. Have I got that correct.

Yes that is correct, but just check that they allow the external impedance of the sub - board to be noted down as Ze as not all of the training centres seem to be singing from the same hymn sheet

 

[Podooser]

Ricicle sorry if this is a stupid question, but what part of the sub-main is the (R1+R2) element of the Zs formula when you do the measurement with the earht connected. Hope that makes sense.

 

[ricicle]

Say the sub - main cable is SWA.
If you are testing the sub - main Zs at the incoming terminals of the board it is feeding then the Ze is at the board feeding the sub - main. The R1 + R2 is the sub - main phase conductor and R2 is the sub - main earth (armouring or core or both)

If it were a 3 phase sub - main there would be a Zs for each phase - same as a 3 phase final circuit

Hope this helps!

 

[Podooser]

The penny has dropped, Ricicle you have been very helpful, thanks.
Regards