2391 Exam

[Mr T]

Good Evening

I have my 2391 Practical exam on Monday and a few concerns that Im hoping you can help me with

Test 1 - Visual inspection find x amount of faults.. im sure I will be OK with this one

Test 2 - 2 x Insulation Resistance tests... we are to do a complete test so am I right in saying it is main switch off but all MCBS switched on ??

The examiner then flicks a switch and puts a fault on the circuit - I guess the logical way to fault find is to knock off an MCB at a time and retest until by process of elimination you find the faulty circuit (however Im told it can be a N-E fault too) is how you would approach this test ?

Test 3- Earth Fault loop Impedance Im Ok with this 1

The its the full test which I aim to tackle in the following steps

1.Safe Isolation

2.Continuity of bonding and protective conductors

3.Polarity

4.Continuity of Ring Final Circuit Conductors

5.IR ( am I right in saying this will be main switch off and all MCB's off as im sure we have to test each circuit individually )

Im confident up to this point but from here I could do with some clarification so please correct me if im wrong but I think this is the order they want

6.Check supply polarity

If all OK is it time to power up ?

If so is it then

7.phase rotation

8.ZE

9.PEFC&PSCC

10.ZS

11.RCD

12.Functional Testing

 

[revjames]

Good EveningI have my 2391 Practical exam on Monday and a few concerns that Im hoping you can help me with

Test 1 - Visual inspection find x amount of faults.. im sure I will be OK with this one

Test 2 - 2 x Insulation Resistance tests... we are to do a complete test so am I right in saying it is main switch off but all MCBS switched on ??

main switch on and test from the leads terminated in connectors

The examiner then flicks a switch and puts a fault on the circuit - I guess the logical way to fault find is to knock off an MCB at a time and retest until by process of elimination you find the faulty circuit (however Im told it can be a N-E fault too) is how you would approach this test ?

sounds like you have the right idea

Test 3- Earth Fault loop Impedance Im Ok with this 1

The its the full test which I aim to tackle in the following steps

1.Safe Isolation prove everything is dead - meticulously

2.Continuity of bonding and protective conductors

3.Polarity

4.Continuity of Ring Final Circuit Conductors

5.IR ( am I right in saying this will be main switch off and all MCB's off as im sure we have to test each circuit individually ) main sw on and bunch test but beware of vulnerable equipment

Im confident up to this point but from here I could do with some clarification so please correct me if im wrong but I think this is the order they want

6.Check supply polarity

If all OK is it time to power up ?

If so is it then

7.phase rotation

8.ZE

9.PEFC&PSCC

10.ZS

11.RCD

12.Functional Testing

Dont forget to test all 3 phases on both sides of the contactor

 

[Mr T]

Dont forget to test all 3 phases on both sides of the contactor

The Motor Circuit - Are you refering to the IR test ?

 

[revjames]

The Motor Circuit - Are you refering to the IR test ?

You need to do the R1+R2 test on all 3 line conductors on both sides of the conductor ie L1 to earth in the CU then test between L1 and earth at the incoming side of the contactor, then do it on L2, then L3 then do it on the side feeding the 3 phase socket too. On the IR test you can push the contactor in with a screwdriver so you test the socket at the same time as L1, L2 then L3.

 

[Mr T]

You need to do the R1+R2 test on all 3 line conductors on both sides of the conductor ie L1 to earth in the CU then test between L1 and earth at the incoming side of the contactor, then do it on L2, then L3 then do it on the side feeding the 3 phase socket too. On the IR test you can push the contactor in with a screwdriver so you test the socket at the same time as L1, L2 then L3.

Yeah Ive got that in the memory bank - is the order of tests that I listed correct ?

Thanks for our help

Stephen

 

[ADS]

Hi Mate,

I've added some things in addition to what Rev has said - hope it helps.

Good EveningI have my 2391 Practical exam on Monday and a few concerns that Im hoping you can help me with

Test 1 - Visual inspection find x amount of faults.. im sure I will be OK with this one Usually 12 faults - pretty straight forward

Test 2 - 2 x Insulation Resistance tests... we are to do a complete test so am I right in saying it is main switch off but all MCBS switched on ??

Test performed on tails haging out of cu - ours was an old wylex with 3036 - make sure main switch is closed

The examiner then flicks a switch and puts a fault on the circuit - I guess the logical way to fault find is to knock off an MCB at a time and retest until by process of elimination you find the faulty circuit (however Im told it can be a N-E fault too) is how you would approach this test ? This is best way - or pull fuses if 3036 - if he dislikes you and puts a neutral to earth fault then you're disconnecting neutrals one at a time

Test 3- Earth Fault loop Impedance Im Ok with this 1

The its the full test which I aim to tackle in the following steps

Errect barriers

1.Safe Isolation Lock off - key in pocket

2.Continuity of bonding and protective conductors

3.Polarity

4.Continuity of Ring Final Circuit Conductors

5.IR ( am I right in saying this will be main switch off and all MCB's off as im sure we have to test each circuit individually )

I tested three phase board in one go - 10 point IR test - outgoing side of main switch, breakers closed, sub-board main switch open, motor contactor open.

Then test between contactor and motor (normally three phase socket)

Then single phase board - test individual circuits, dimmer removed, breakers open (RCD main switch) - I think there's only two/three circuits anyway.

Don't forget to throw the two way switch

Im confident up to this point but from here I could do with some clarification so please correct me if im wrong but I think this is the order they want

6.Check supply polarity yes

Ze here before energising - reconnect earthing conductor

PFC here

If all OK is it time to power up ? Then power up

If so is it then

7.phase rotation - Shouldn't have to do this one - but you may

8.ZE

9.PEFC&PSCC

10.ZS

11.RCD

12.Functional Testing

He may then ask how you would calculate or measure volt-drop

Good luck

 

[revjames]

Good advice, sounds like you will be well prepared. Just one thing, when you do the live tests, make sure you close up the main board before going to the "upstairs" board. Leaving the main board unnattended will amount to a possible fail as you will be seen to be leaving a DB open, live and unattended.

 

[Mr T]

Hi Mate,I've added some things in addition to what Rev has said - hope it helps.

have my 2391 Practical exam on Monday and a few concerns that Im hoping you can help me with

Test 1 - Visual inspection find x amount of faults.. im sure I will be OK with this one Usually 12 faults - pretty straight forward

Test 2 - 2 x Insulation Resistance tests... we are to do a complete test so am I right in saying it is main switch off but all MCBS switched on ??

Test performed on tails haging out of cu - ours was an old wylex with 3036 - make sure main switch is closed ( so main switch closed/on and MCB's on , I guess this is because there is no Live incoming supply ? )

The examiner then flicks a switch and puts a fault on the circuit - I guess the logical way to fault find is to knock off an MCB at a time and retest until by process of elimination you find the faulty circuit (however Im told it can be a N-E fault too) is how you would approach this test ? This is best way - or pull fuses if 3036 - if he dislikes you and puts a neutral to earth fault then you're disconnecting neutrals one at a time (yeah I heard about this )

Test 3- Earth Fault loop Impedance Im Ok with this 1

The its the full test which I aim to tackle in the following steps

Errect barriers

1.Safe Isolation Lock off - key in pocket

2.Continuity of bonding and protective conductors

3.Polarity

4.Continuity of Ring Final Circuit Conductors

5.IR ( am I right in saying this will be main switch off and all MCB's off as im sure we have to test each circuit individually )

I tested three phase board in one go - 10 point IR test ( this being L1-E, L2-E,L3-E, N-E, L1-N,L2-N,L3-N,L1-L2,L1-L3,L2-L3)- outgoing side of main switch, breakers closed, sub-board main switch open, motor contactor open( so this tested up to the contactor)

Then test between contactor and motor (normally three phase socket) and this tested from the contactor ??

Then single phase board - test individual circuits, dimmer removed, breakers open (RCD main switch) - I think there's only two/three circuits anyway.

Don't forget to throw the two way switch

Im confident up to this point but from here I could do with some clarification so please correct me if im wrong but I think this is the order they want

6.Check supply polarity yes

Ze here before energising - reconnect earthing conductor

PFC here (so PFC before energising ? )

If all OK is it time to power up ? Then power up

If so is it then

7.phase rotation - Shouldn't have to do this one -

8.ZE

9.PEFC&PSCC

10.ZS

11.RCD

12.Functional Testing

He may then ask how you would calculate or measure volt-drop

 

[ADS]

Hi,

My initial IR tests were on a 'portable' board specially for the purpose - so, yes, no power connected, just tails and earthing conductor hanging out the bottom.

The procedure you described for the IR test on three phase board is spot on.

You do your PFC straight after your Ze on incommers, but with the earthing conductor reconnected (as you probably know), but before energising the installation - I'd say the reason for this is to confirm the PFC is lower than the breaking capacity of your MCBs before putting them back into service.

Cheers

 

[ADS]

Hi again,

just a couple of other things you might find usefull.

With it being a periodic you can do the tests in any order - whatever makes most sense, really.

When doing Zs, it's the extremity of every circuit, every socket and don't forget the Zs of the single phase board - you also take a PFC reading for the single phase board at the same time.

Measuring Zs of motor circuit from the contactor is probably easiest then add th R1+R2 value of contactor to motor - this is acceptable.

Hope Ive been a help

 

[Mr T]

Hi again,Hope Ive been a help

A huge help many thanks

 

[revjames]

I got told off for doing IR before CPC continuity, in hindsight he had a point but still passed

 

[the doctor]

Hi

good responses with lots of info for you, but a bit more!

you are doing a periodic so you can test any order you like

i think the quickest order is this

safe isolation including incoming polarity

Ze

PFC

Continuity of radials on bottom board (from this calc Zs, Zs=Ze +(R1+R2)

Ring test on bottom board

IR test on bottom board- dont forget to test between lines on leg to 3 phase socket AND test at the 3 phase socket "backwards" to starter.

at top board, use the Zs figure as your incoming Zdb (transfer of origin)

no need to do PFC but you could measure later or calculate.

on top db then test....

continuity (dont forget to remove and short out dimmer wiring)

do add up of Zs again.

IR (leave short on dimmer wiring and dont forget 2 way switches)

lid up, ask permission to fire up and do rcd test

then lastly do safe isolation again on top board and re-fit dimmer

fire up and make sure it all works.... :z

best wishes

alan

 

[ADS]

i think the quickest order is this

safe isolation including incoming polarity

Ze

PFCContinuity of radials on bottom board (from this calc Zs, Zs=Ze +(R1+R2)

Ring test on bottom board

IR test on bottom board- dont forget to test between lines on leg to 3 phase socket AND test at the 3 phase socket "backwards" to starter.

Hi Alan,

I did consider doing this on my 2391, but was put off by the lecturer giving us the order of tests that I mentioned in my earlier post.

I certainly agree with you and it's what I do on a PIR.

The only other thing I would say is that he did want to see me test Zs, not calculate.

I think the only exception was the motor circuit/socket - there I did Zs at contactor and then added R1 + R2 of remainder of circuit to that.

Cheers

 

[the doctor]

Hi Alan,I did consider doing this on my 2391, but was put off by the lecturer giving us the order of tests that I mentioned in my earlier post.

I certainly agree with you and it's what I do on a PIR.

The only other thing I would say is that he did want to see me test Zs, not calculate.

I think the only exception was the motor circuit/socket - there I did Zs at contactor and then added R1 + R2 of remainder of circuit to that.

Cheers

Hi ADS.

And there lies the problem, a personal prejudice of the assessor. If it is in the GN3 then it is on, for sure.- i dislike dogma in the industry!

and me? well i advise in class the easy way but when they turn up for assessment i have seen them doing an rcd test first and i say "fill yer boots kid!" good on em!

 

[the doctor]

hi

another example for you....

when they do a PFC on the bottom board they get say 0.6kA which they then double as it is a polyphase supply.

they then record the breaking capacity of the mcbs at 6kA

so when they get to the top board i tell them to put a line through the PFC section of the test schedule as it is completely irrelevant

remember the GN3 states "at all relevant points"

you would not believe the hassle i get off the "academics" on moot points like this

i love being a maverickX(

 

[choccy]

Hi,My initial IR tests were on a 'portable' board specially for the purpose - so, yes, no power connected, just tails and earthing conductor hanging out the bottom.

The procedure you described for the IR test on three phase board is spot on.

You do your PFC straight after your Ze on incommers, but with the earthing conductor reconnected (as you probably know), but before energising the installation - I'd say the reason for this is to confirm the PFC is lower than the breaking capacity of your MCBs before putting them back into service.

Cheers

just a quick reply the pfc is a live test and therefore cant be done after the ze, the earth bond as you said should be reconnected and when supply on test the both pefc and the pssc then you would record the highest as your pfc. ?:| ut the kettle on

 

[ADS]

hianother example for you....

when they do a PFC on the bottom board they get say 0.6kA which they then double as it is a polyphase supply.

they then record the breaking capacity of the mcbs at 6kA

so when they get to the top board i tell them to put a line through the PFC section of the test schedule as it is completely irrelevant

remember the GN3 states "at all relevant points"

you would not believe the hassle i get off the "academics" on moot points like this

i love being a maverickX(

Agreed - I assume you are referring to the fact that the breakers in the single phase board ar more than adequate to handle the fault current at the origin, so no need to measure PFC at the remote board, as it will be lower

 

[ADS]

just a quick reply the pfc is a live test and therefore cant be done after the ze, the earth bond as you said should be reconnected and when supply on test the both pefc and the pssc then you would record the highest as your pfc. ?:| ut the kettle on

PFC is a live test, but so is Ze - but the installation isn't 'Live'.

You don't need the installation energised to measure PFC - you can take the measurements on the incomming side of the open main switch.

As the doctor correctly stated, Supply Polarity, Ze and PFC can all be done first, after safe isolation of installation, but before the dead tests - you might as well do the three whilst your there

 

[choccy]

yous are very correct i should have read the post properbad day explodebad day explode:good night:ly.