2391 practical exam

[Sparks74]

I have my practical exam in a week & haven't really done any 3phase testing & i am led to belive that there is a 3 phase motor circuit on the rig?

So what i'm asking is how would i carry out an R1+R2 test on it & also the Zs & finally what do i need to do with it in regards to IR test were the contactor is concerned?

Any help would be greatly appreciated

Thanks

 

[Sparky Ninja]

With the motor circuit you carry out the tests as the following:

R1&R2 carried out between L1-CPC, L2-CPC & L3-CPC respectively.
At the motor starter switch you can remove the cover and measure from the consumer unit to the terminals supplying the unit. Then you can separately measure the R1&R2's from the unit to the motor terminations, then add the two measurements together for a total R1&R2 value for each line.

Regarding the insulation resistance, with the cover off the starter it is likely to already be disconnected from any sensitive equipment on the supply side.
Carry out the insulation resistance test between Live conductors, and between Live conductors and CPC.
This can be repeated on the load side of the motor starter switch, HOWEVER make sure that the connections are free from any loads..

The EFLI test will depend on the centres setup and interpretation of the building regulations. They make expect you to do the calculation for Zs or they may allow you to carry out a live measurement. The important thing to remember is that a EFLI must never be carried out on the motor itself as it may cause the motor to rotate while under test. If you are able to take a live measurement, the simple procedure will be to carry out the live test to the supply side of the switch starter, and then just add the extra R1&R2 to that Zs reading to incorporate the cable to the motor itself.

 

[pushrod]

when i did it we had 1 rcbo which we removed - then did IR on whole installation via the tails, linking L1, L2and L3 together.

Most Zs were calculated - i think most centres just do live Zs test on sockets via plug lead.

 

[Sparky Ninja]

we don't




a dying breed.

 

[pushrod]

we don't




a dying breed.

you've obviously got good insurance

 

[Sparks74]

Thanks guys,

Just a few more questions if you dont mind,
I have been told that as part of the exam there is small rig with 12 faults on it,am i right in assuming that this is just a visual inspection & i'm basically looking for things like loose connections,to much copper showing,reverse polarity etc?Also when doing IR tests i tend to do 1 circuit at a time but due to time constraints was going to do the IR test on the main rig for the PIR as a one main one for the whole board so was wondering what is the best & quickest way to do this bearing in mind that it will incorparate a least 1 RCD?

Finally as far as the exam is concerned theres the PIR on the main rig,the 12 visual faults,& apparently faults to be found doing an IR test
& one more unit that i dont know could anyone please enlighten me?

Many thanks

 

[Sparky Ninja]

The inspection assessment is 30 minutes in length.

A board will be setup with some deliberate scenarios put in which you will need to identify as an observation. These could be faults (like incorrect polarity) or just minor observations (like incorrect identification of conductors). The assessor will have a list with a specific 12 on there, and you need to find them. I always ask my guys to use the whole 30 minutes and make an exhaustive list, because if I told them there were 12, they would get to 12 and stop looking.

It is worth remembering that the setup of the board, as requested by C&G, is in a way that some of the observations on the list may be combined in one location.


Regarding the IR test just remember to remove any sensitive equipment. Particularly the motor control, lamps and DIMMER switch.
Carry it all out in bulk, and if anything comes up, knock the mcb's off one at a time.
Any reading you get for IR will most likely come from the fire alarm circuit, as this should be wired in MI, which naturally, can have a IR not exceeding the maximum.
The RCD is most likely to be in the sub db, in this case you can just isolate it and test downstream from it on the other board.


So practical exams you have:

The PIR - 2 hours
The IR board - 20 minutes
The inspection board - 30 minutes

The fourth is the EFLI rig. It's only 10 minutes.
With this rig, you will be asked to carry out a loop test on each of two circuits. The rig will be small, and consist of a board with 2 sockets on it, 1 on a ring circuit and 1 on a radial (the centre you use may have just one socket, with a selector switch).
The assessor will have a predetermined list of conditions and will switch one of them in.
You will be given an ambient temperature, and asked to carry out a loop test. You will then record the reading obtained, and work out from the OSG the maximum permitted Zs. Then you conclude if it is acceptable or not.
It is worth remembering that the assessor has an option to remove the earth with one of the switches. The will result in your selected tester illustrating to you that the socket has incorrect polarity or is unsafe.. IF YOU CARRY ON AND ATTEMPT TO PRESS THE 'TEST' BUTTON it would be an immediate FAIL.

 

[pushrod]

Thanks guys,

Just a few more questions if you dont mind,
I have been told that as part of the exam there is small rig with 12 faults on it,am i right in assuming that this is just a visual inspection & i'm basically looking for things like loose connections,to much copper showing,reverse polarity etc?
Yes a lot of little things on a small board - i remember the last fault i found was a 13A fuse in an fcu to lighting.

Also when doing IR tests i tend to do 1 circuit at a time but due to time constraints was going to do the IR test on the main rig for the PIR as a one main one for the whole board so was wondering what is the best & quickest way to do this bearing in mind that it will incorparate a least 1 RCD?
As i said earlier, we had an rcbo - removed that and put in pocket - made a little table for results and tested all lines to N, all lines to cpc , and L1 to L2 etc .Then did the circuit that had the rcbo on.
Finally as far as the exam is concerned theres the PIR on the main rig,the 12 visual faults,& apparently faults to be found doing an IR test
Yep very straight forward - 3 circuits if i recall and just had to find and identify what the fault was eg open circuit between L and N
& one more unit that i dont know could anyone please enlighten me?

We also had a Zs test to do and check if value was acceptable - just had to remember to look in the correct table in BS 7671 and use 0.8 (rule of thumb) of value in the book
.Many thanks

In red, hope that helps. I must admit i was very nervous before hand but the guys running it were pleasant and weren't trying to trip you up or anything, and it wasn't as bad as i imagined. - good luck

 

[tony mc]

Best of luck with the assessment excellent replys on the thread.

When looking for the faults or non compliance with BS 7671 don't forget your IP codes especially for consumer units IPXXB or IP2X & IPXXD or IP4X

 

[SirKit Breaker]

Thanks guys,

Just a few more questions if you dont mind,
I have been told that as part of the exam there is small rig with 12 faults on it,am i right in assuming that this is just a visual inspection & i'm basically looking for things like loose connections,to much copper showing,reverse polarity etc?Also when doing IR tests i tend to do 1 circuit at a time but due to time constraints was going to do the IR test on the main rig for the PIR as a one main one for the whole board so was wondering what is the best & quickest way to do this bearing in mind that it will incorparate a least 1 RCD?

Finally as far as the exam is concerned theres the PIR on the main rig,the 12 visual faults,& apparently faults to be found doing an IR test
& one more unit that i dont know could anyone please enlighten me?

Many thanks

Don't be worried about the time, and dont watch the clock. 2 hours is enough on the PIR rig. I got off to a crap start doing mine, and with my experience of testing it should have been a breeze. It took me 20 minutes to get into the swing of it, and to start thinking properly. Once i got going, and into the rhythm i flew through it in about an hour and a half, and that included fixing the test rig as it kept falling apart, but then the real life situation in most older CU's is no different.

Cheers.........Howard

 

[SirKit Breaker]

Best of luck with the assessment excellent replys on the thread.

When looking for the faults or non compliance with BS 7671 don't forget your IP codes especially for consumer units IPXXB or IP2X & IPXXD or IP4X

The one that nearly caught me out was a missing earth connection from the SWA gland to the earth terminal, and i have connected loads of isolators and motors so it should have hit me in the face.

Cheers.........Howard

 

[john25]

for the Motor circuit on the 2391 I only have to do a R2 test on it as it will save time obviously this will have to be followed up with a LIVE Zs test