Basic Testing Procedures

[WayneL]

In the 2391 the 1st thing you do is safe isolation anyhow so you can't do a live test first as an isolator feeds your board (at least mine did) but generally at an occupied building of course the way you said is the choice a lot of sparks would command to. Though i believe however you do them you still take the same amount of time doing the individual tests any which way as you don't go quicker with individual tests doing them in different orders.
Anyways its each to there own, we all have our own way of doing things. My main worry was for anyone reading this article as it was before being edited that are about to sit there 2391 practical, not for those who test day in day out, they are confident and can do it however they feel at ease to.

The correct way (as you are supposed to be isolating a live supply) is for the isolator feeding your board to be closed.

You isolate the installation by opening the three phase main switch then proving dead.
This doesn't have the same effect if the 'main isolator' to the 2391 board is already open.

My examiner actually told me to go across the incommers with the same 'ten-point' test that I performed for safe isolation - this, of course, proved supply polarity.

He then closed the 'main isolator' and locked it off.

The time saved is in the efficiency of testing - for instance: no point in having to take the cover off the board again to do tests you could have done earlier.

 

[WayneL]

The correct way (as you are supposed to be isolating a live supply) is for the isolator feeding your board to be closed.

You isolate the installation by opening the three phase main switch then proving dead.
This doesn't have the same effect if the 'main isolator' to the 2391 board is already open.

My examiner actually told me to go across the incommers with the same 'ten-point' test that I performed for safe isolation - this, of course, proved supply polarity.

He then closed the 'main isolator' and locked it off.

The time saved is in the efficiency of testing - for instance: no point in having to take the cover off the board again to do tests you could have done earlier.

I've just read my post and realised the stupidity in what I have said - So ignore me and do what you think is best.

Either way is fine.

 

[SafetyFirst]

No bother at all Wayne its good that we share all our own ways of doing things it can only be of benefit. I am currently on a 2391 course so i can only speak of how i've been learning and having done the practical already my expirience so far.

 

[shill]

Thank you for explaning that helps alot. is there any chance of explaning what the readings mean eg. greater than 1M ohm, also the reading for insulation resistance. as this confuses me and dont understand a good reading from a bad one. cheers

 

[RexT]

Hi Safety First,

I think I saw the CRIPPLER way of remebering the tests from either Chris Kitcher or Dave Potter. There is a second P which reminds polarity Live test as well as the polarity dead test.
Great way of remembering, thanks,

Best wishes,

Rex

 

[vbyrne]

Safe isolation



The procedure for proving dead should be by use of a test lamp or two pole voltage detector as recommended in HSE Guidance Note GS38.
Non-contact voltage indicators (voltage sticks) and multi-meters should not be used. The test instrument should be proved to be working on a known live source or proprietary proving unit before and after use. All phases of the supply and the neutral should be tested and proved dead.




Test sequence and descriptions



The following tests are carried out with the Consumers main switch isolated



1. Extenal earth fault loop impedance


Reason: To establish that a good earth exists at the installation in order for the remaining tests to go ahead.


Method: Disconnect the main earthing conductor from the main earthing terminal. An earth fault loop impedance tester is connected at line and earth (main earthing conductor) at the supply side of the installation and a test performed. Reconnect the main earthing conductor. The result is Ze and recorded on the sheet. The prospective fault current is measured at the same time after the reconnection of the main earthing conductor.


2. Continuity of protective and bonding conductors


Reason: To check that all circuit protective conductors (green and yellow cables) are continuous and are present at every electrical accessory on the circuit. Also to check that the main earthing conductor and main bonding conductors are continuous and correctly connected.


Method 1: The line conductor is connected to the circuit protective conductor of the same circuit at the consumer unit and a measurement taken at ALL accesories on that circuit between line and c.p.c. The highest measurement obtained is recorded on the test report.
Test result is R1 + R2. The line conductor and neutral conductor are then connected and the above repeated to obtain R1 + Rn


Method 2 (used for main earth and main bonding conductors): A wandering lead is connected to one end of the conductor to be tested and a measurement taken between the other end of this lead and the other end of the conductor.
Test result is R2.
During this test polarity can be checked as well. The continuity of the neutral conductor can also be checked.


3. Continuity of ring final circuit conductors


Reason: This test ensures that all ring final circuits (sockets usually) are indeed a continuous ring with no interconnects or breaks within it.

Method: The line, neutral and earth conductors of the circuit are identified and a measurement from one end to the other end of each is taken. These results are r1, r2 and rn.
The incoming line conductor is then connected to the outgoing earth conductor and the outgoing line conductor is connected to the incoming earth conductor. A measurement is then taken at ALL socket outlets on the ring. The highest of which is recorded on the report.
This result is R1+R2 for that circuit. The above is then repeated using the neutral conductor instead of the earth conductor. This test provides R1+Rn which does not need to be recorded on the report but is essential to check the circuit correctly.


4. Insulation Resisitance


Reason: This test checks whether the insulation around a cable is still intact and has not broken down over time. It is a good indicator of the age of an installation.

Method: An insulation resistance tester is connected across line and neutral tails at the origin of the supply. 500V are then pumped down the conductors to see if any voltage leaks across from one conductor to the other. The same is then done for the line and earth and the earth and neutral conductors.


5. Polarity


Reason: To check that all accesories are correctly connected to line, neutral and earth and that all switches and circuit breakers are connected in the line conductor only.

Method: The method for this is the same as for continuity and is usually done at the same time by operating switches etc whilst conducting the test.


6. Earth electrode resistance


Reason: To make sure that any earth electrode used is of a sufficiently low impedance to allow the timely operation of the RCD protecting the installation.

Method: An earth fault loop impedance tester is connected between line and earth at the origin of the supply and a test performed. The result of which is considered the resistance of the electrode (Ra).



The following tests are carried out with the Consumers main switch energised




7. Live polarity test


Reason: To verify polarity of supply authorities system.


Method: An approved voltage indicator shall be used or test lamp to GS38. Using the approved voltage indicator, one probe shall be placed on the incoming neutral, and the other on the incoming line conductor, on the main breaker. The indicator should show it is live. One probe shall now be placed on the CPC and the other on the incoming line conductor. The indicator should show it is live. A test shall be preformed between CPC & incoming neutral. The indicator should show that it is not live.


8. Earth fault loop impedance


Reason: This test is done at the furthest point on a circuit in order to make sure the impedance of the earth path is not too high even at the furthest point so that sufficient current will flow under fault conditions to take out the circuit breaker protecting the circuit.

Method: An earth fault loop impedance tester is connected to line and earth at the furthest point on the circuit and the test performed.


9. RCD test


Reason: To make sure RCD's trip within the correct time

Method: An RCD tester is connected and a test at 1/2 times, 1 times and 5 times the trip current is performed and a time of trip obtained. Usually milli-seconds. The test button is then pressed.


10. Functional testing

Reason: To make sure all switches, isolators, MCB's etc. work as they should.

Method. Self explanatory.

i have just started to test and I would like you to tell me if you could how to fill in the test sheets that I have to fill in Q.1.In the circuit details for the installation, there is a column 'Reference Method', what is this?

 

[Guest123]

i have just started to test and I would like you to tell me if you could how to fill in the test sheets that I have to fill in Q.1.In the circuit details for the installation, there is a column 'Reference Method', what is this?

It refers to the installation method of the cable/wiring system and it's associated reference method.

You'll find them on P261 in BS 7671.

 

[vbyrne]

It refers to the installation method of the cable/wiring system and it's associated reference method.

You'll find them on P261 in BS 7671.

what is a PSCC test and what do the results of this test tell you

 

[Sintra]

PSCC Prospective short circuit current measured between L & N

PEFC Prospective earth fault current measured between L & E

PFC Prospective fault current the highest reading from the 2 tests above.

The results of this test allow you to calculate the size of the main earthing conductor and to select the type of overcurrent device to be used.

 

[vbyrne]

Thanks for that mate,this is all good info,when I am out on site I dont get the chance to ask these kind of questions all everybody wants todo is get the results down on the sheets and fill the rest of them out at home. I have another,we are working in a large factory,we can not get to the main dis board that supplys all the sub boards but on the sheet that I was given there is a section for parameters of supply with Zs one of the box to be filled in do I take this reading at all my sub boards as well as the main board.

 

[Jurasic Spark]

Hi Safety First,

I think I saw the CRIPPLER way of remebering the tests from either Chris Kitcher or Dave Potter. There is a second P which reminds polarity Live test as well as the polarity dead test.
Great way of remembering, thanks,

Best wishes,

Rex

Your right, the second P is Live polarity which is done on the supply side of the isolator before turning it ON!!
Regards D.P

 

[Jurasic Spark]

Thanks for that mate,this is all good info,when I am out on site I dont get the chance to ask these kind of questions all everybody wants todo is get the results down on the sheets and fill the rest of them out at home. I have another,we are working in a large factory,we can not get to the main dis board that supplys all the sub boards but on the sheet that I was given there is a section for parameters of supply with Zs one of the box to be filled in do I take this reading at all my sub boards as well as the main board.

I think you mean Ze and there is only one Ze on any installation and that is where the suppliers cables end and the installation cables begin

 

[vbyrne]

PSCC Prospective short circuit current measured between L & N

PEFC Prospective earth fault current measured between L & E

PFC Prospective fault current the highest reading from the 2 tests above.

The results of this test allow you to calculate the size of the main earthing conductor and to select the type of overcurrent device to be used.

at this stage would the earth and protective device be in place

 

[vbyrne]

I think you mean Ze and there is only one Ze on any installation and that is where the suppliers cables end and the installation cables begin

so Ze is at the main incomer and Zs can be measured at every other fitting,and what does this tell you,the Zs that is?

 

[Sintra]

at this stage would the earth and protective device be in place

Yes at this stage the main earthing conductor will have been reconnected back into the MET the main switch will be in the open (off) position. Test carried out at incoming side of main switch.