consumer unit testing question

[pablod]

hi,

when changing over a consumer unit is it correct practice to test R1 and R2 on all fittings on all circuits or is it acceptable to test on the point furthest on each circuit.

one other point. am i correct in saying on the light it is ok on the IR test (at 500v) to connect line and neutral together to earth. half the house is low voltage lighting and testing this way means i wont have to dissconnect the transformers?.

thanks for ya help in advance. im newley qualified and have a consumer unit chane next week for me assessment.

 

[Sickmick]

Short answer yes and yes. When changing a consumer unit you're under no obligation to test the installation, however it's best practice to carry out a periodic inspection so just make a note of your limitations in testing.

 

[Des 56]

The alteration or addition itself (the installation of
the replacement consumer unit and any other new
work, such as additional final circuits) should be
verified fully in accordance with the requirements of
Section 610 of BS 7671 and an Electrical
Installation Certificate in accordance with BS 7671,
detailing the work, should be given by the installer to
the customer.
10.2. In addition, as a minimum, the following tests
should be carried out to the existing circuits
connected to the replacement consumer unit.
• A continuity test of the protective conductor of
each circuit, to the point or accessory electrically
furthest from the consumer unit and to each
accessible exposed-conductive-part.
• A continuity test of all ring final circuit
conductors.
• A measurement of the combined insulation
resistance of all the circuits. The measurement
need only be made between the line and neutral
conductors connected together and the
protective conductor connected to the earthing
arrangement.
• A test of the polarity and a test to establish the
earth fault loop impedance (Zs
), at each
accessible socket-outlet and at least one point or
accessory in every other circuit, preferably the
point or accessory electrically furthest from the
consumer unit.
Note: Testing of each RCD using both a test instrument




The above is copied and pasted from here, its worth reading
http://109.75.163.57/fileadmin/user_upload/documents/industry/best_practice/BPG6_09.pdf

 

[pablod]

cheers for that guys one thing i just want to check on. when IR testing at 500v and combining line and neutral it is ok to leave transformers and all ights connected. i dont want to be doing any damage as this would be the first time im doing the line and neutral together as i have done all my testing the standard way.

cheers

 

[cjp1]

When doing a cu change I like to R1 + R2 at all points on all circuits as even if you have continuity at the most remote point of a circuit it does not mean you will at all other upstream points.
If all is well you should get the highest reading from the most remote point on that circuit which will be recoreded as R1+R2 for that circuit but this is not always the case.
When doing IR test you could use a shorting lead at the cu on the live and neutral and test between live/neutral and earth, But you must remember to remove the link before re-energising the supply.

 

[pablod]

hi and thanks cjp1,

the way i was shown when training was to connect line and neutral in a block and leave the cpc in the earth bar. just checking this is the same. i beleive it is.

paul

 

[cjp1]

I need to learn to type quicker

 

[cjp1]

hi and thanks cjp1,

the way i was shown when training was to connect line and neutral in a block and leave the cpc in the earth bar. just checking this is the same. i beleive it is.

paul

Hi Paul, I am not quite sure what you mean about connecting the line and neutral in a block?
you could make a tempory connection between line and cpc using a connector block at the consumer unit when doing you R1+R2 for a radial circuit.
cheers chris

 

[Des 56]

Be careful that you are sure and safe
I find the easiest of all methods is to switch off the supply,engage all mcbs and link with a wire with crocodile clips from the bus bar/s to the neutral bar/s and test between the bus bar or neutral bar and the earth terminal

 

[pablod]

hi des,

i take it that method is what they mean by testing the combined IR of all circuits

cheers

 

[pablod]

hi chris,

i ment connect the line and neutral in a connector block when doing IR test and then connect to earth.

 

[Des 56]

Yes.its sometimes referred to as a global test
The insulation resistance test should be done as whole installation test

 

[Deleted member 26818]

Then if the readings are off, test each circuit individually.

 

[Richard Burns]

If you are testing the whole installation then do not use a connector block, as you would need to connect every line and every neutral into the block. The connector block would only be used for testing a single circuit. However it is easier to just link them as mentioned above.
A 500V test should not damage anything but check at 250V first and if you get a low reading check for delicate items in circuit. ELV light transformers and dimmer switches should ​ be OK.

 

[daiplayer]

cheers for that guys one thing i just want to check on. when IR testing at 500v and combining line and neutral it is ok to leave transformers and all ights connected. i dont want to be doing any damage as this would be the first time im doing the line and neutral together as i have done all my testing the standard way.

cheers

When you connect the line and neutral at the board , you take away the possibility of high current ( due to 500v going down it) going through the tx / lights/ aplliances ....since current will only flow from 230v - 0v....or 200 - 50 ..../ any place with a difference between the voltage ( ie potential difference )

Connecting live and neutral means you put 500v on the l+n at the same time. so no currents.

Hope this helps and im correct. LOL