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In the OSG (red edition) it says - main switch off .... switches and circuit breakers closed.

Yet figure 10.6 on page 84 clearly shows that the circuit breakers are open/off??

Why is this?


I just had a quick look at the old red OSG, the first test with the mains switch off and all circuit breakers on is a global test between live conductors (L-N if SP) but not including the tails, the picture fig 10.6 is testing individual circuits between live conductors, ie. main switch off and circuit breakers off, but in fairness this is not explained in the text.
 
Am going to have a look at it again tomorrow. I know the person and am using the CU to get used to testing so have permission to probe away.

1) When testing on the remote cu do i also have the main switch off on the main Cu in the house as well??

2) And also (opposite of above), when testing on the main cu in house should remote cu main switch be off?

3) And to clarify should circuit breakers be in the off/open position or on/closed position?

1+2) If you are a doing a global test of the whole installation then you are testing the remote CU as well so the remote CU switch would be ON. If you are trying to break things down then you can leave the remote switch off and test the main CU installation and then with the remote switch still off test the remote CU installation.
Think about what you need, the power must be off and the electrical connections around the whole installation must be connected.

3) For a global test of an installation all the circuit breakers should be on and the main switch off.
 
Thanks for the help guys.

I dont mind running into problems testing as best way to learn how to find faults. Having this forum gives you more confidence and makes you realise that you're always learning.

Thanks again.
 
So in reference to my earlier post:

1) When testing on the remote CU do i also have the main switch off on the main CU in the house as well??


2) And also (opposite of above), when testing on the main CU in house should remote CU main switch be off?

3) And to clarify should circuit breakers be in the off/open position or on/closed position?


1) you need to isolate the remote CU from being powered, as the IR test is a dead test, this depends on how the remote CU is powered eg. by an MCB from the main CU ?, if it is powered via an MCB in the main CU then this needs to be off/open.

2) depends on if you are testing both cu's together

3) this depends if you are testing all the circuits together (global) or indvidually. If all MCB's are on then all of the L conductors will be connected together via the L comb/busbar this is global, if they are in the off position you will need to test each one at the out going side of each MCB.
 
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1) you need to isolate the remote CU from being powered, as the IR test is a dead test, this depends on how the remote CU is powered eg. by an MCB from the main CU ?, if it is powered via an MCB in the main CU then this needs to be off/open.

2) depends on if you are testing both cu's together

3) this depends if you are testing all the circuits together (global) or indvidually. If all MCB's are on then all of the L conductors will be connected together via the L comb/busbar this is global, if they are in the off position you will need to test each one at the out going side of each MCB.

With regard to the above answer in red:

So doing an IR test on main cu in house AND with the remote cu main switch on - this was why I was getting a fail on my ir test between n-e?

As in post number 15 indicates that there is a fault in the outbuilding but you have indicated that the outbuilding cu main switch should be in the off position anyway (which when it is off clears the fail on the ir test)???
 
If it is any consolation Chrisgc, the same mistake in the diagrams is carried over in the new GN3, ie. it shows testing an individual circuit but showing all of the MCB's on when they should be off.
 
If it is any consolation Chrisgc, the same mistake in the diagrams is carried over in the new GN3, ie. it shows testing an individual circuit but showing all of the MCB's on when they should be off.

OSG (red) page 84 figure 10.6 - Are the MCB's off?? It looks like they are off - are they??

But description on page 83 states circuit breakers closed (on)?
 
With regard to the above answer in red:

So doing an IR test on main cu in house AND with the remote cu main switch on - this was why I was getting a fail on my ir test between n-e?

As in post number 15 indicates that there is a fault in the outbuilding but you have indicated that the outbuilding cu main switch should be in the off position anyway (which when it is off clears the fail on the ir test)???


Richard answered this further back, You would then break the installation down further, turn off the remote CU main switch, turn all MCB's off in the remote CU, and then test each outgoing side of each MCB in the remote CU and then you will be able to identify which circuit is giving the faulty reading.
It is a question of elimination.

BTW on an existing installation it is usually better to link your L-N and test to earth in case a load is still connected, it is also wise if you are going to test between L-N to test at 250V first (soft test), in case you damage something such as central heating controllers, alarm panels, aerial amplifiers and the like which may still be connected.
 
Richard answered this further back, You would then break the installation down further, turn off the remote CU main switch, turn all MCB's off in the remote CU, and then test each outgoing side of each MCB in the remote CU and then you will be able to identify which circuit is giving the faulty reading.
It is a question of elimination.

BTW on an existing installation it is usually better to link your L-N and test to earth in case a load is still connected, it is also wise if you are going to test between L-N to test at 250V first (soft test), in case you damage something such as central heating controllers, alarm panels, aerial amplifiers and the like which may still be connected.

Linking L-N and test to earth - Is this perfectly acceptable if and when assessed by an assessor for competent person schemes? (long way off yet).
 
OSG (red) page 84 figure 10.6 - Are the MCB's off?? It looks like they are off - are they??

But description on page 83 states circuit breakers closed (on)?


Yes they are off lol, but it does not match the text in the red OSG, that drawing should be in the new GN3 for testing indvidual circuits, or at least the labelling.
 
Linking L-N and test to earth - Is this perfectly acceptable if and when assessed by an assessor for competent person schemes? (long way off yet).

Yes perfectly acceptable on an existing installation, on a new build or rewire and the like you should do the L-N test on the cables before the accessories are fitted.

As I said some items don't like 500V up 'em, and it is possible to damage vunerable equipment, and on a job if you break it you have to fix it/replace it, and some central heating controller panels and the like are bloody expensive.
 
Yes perfectly acceptable on an existing installation, on a new build or rewire and the like you should do the L-N test on the cables before the accessories are fitted.

As I said some items don't like 500V up 'em, and it is possible to damage vunerable equipment, and on a job if you break it you have to fix it/replace it, and some central heating controller panels and the like are bloody expensive.


Totally understand about doing the 250v IR test first.

Is it not wise for electricians to have a brief disclaimer form for when assessing or testing installations (for IR test), in case something is blown due to voltage being put through?

Just a thought really as we sign forms for many things in life like operations, dental treatment etc for experts in their field to operate yet if anything goes wrong they have you sign disclaimer beforehand to cover themselves.

Would it not be an idea for electricians too and prudent in the likely hood that something was damaged by mistake?
 
Totally understand about doing the 250v IR test first.

Is it not wise for electricians to have a brief disclaimer form for when assessing or testing installations (for IR test), in case something is blown due to voltage being put through?

Just a thought really as we sign forms for many things in life like operations, dental treatment etc for experts in their field to operate yet if anything goes wrong they have you sign disclaimer beforehand to cover themselves.

Would it not be an idea for electricians too and prudent in the likely hood that something was damaged by mistake?

By linking the L to N you remove the risk all together, the other option is to double check that everything is disconnected by testing at 250V first, and only if that is clear then do the test at 500V, you can also link/bypass any vunerable equipment.
Again it is better to test @ 250V first in case you have missed something.

I would only bother with the L-N test if it was a newly installed circuit/s that I know exactly what is what, but on a CU change and an EICR etc. I just do the L+N to E test, as I said this is an acceptable method..

Sometimes Neon indicators on shower switches and the like give false readings on the L-N test.
 
I have just re-read your earlier posts and you say you have a N-E fault at the remote CU, as the MCB's are single pole devices turning these on or off in the remote CU won't isolate or narrow your fault down.

I would start by opening the main switch at the remote CU then test between N and E bars, if your fault is now clear then it may be a supply cable fault, if it it is still reading faulty then you will have to do as some of the other posters have said much further back in the thread, and start disconnecting the Neutrals from the N bar in the remote CU, and test each one to earth, this will at least narrow it down to one circuit, unless you are really unlucky and have more than one fault lol.

Edit: do you have any RCD's or RCBO's in the remote CU ?
 
I have just re-read your earlier posts and you say you have a N-E fault at the remote CU, as the MCB's are single pole devices turning these on or off in the remote CU won't isolate or narrow your fault down.

I would start by opening the main switch at the remote CU then test between N and E bars, if your fault is now clear then it may be a supply cable fault, if it it is still reading faulty then you will have to do as some of the other posters have said much further back in the thread, and start disconnecting the Neutrals from the N bar in the remote CU, and test each one to earth, this will at least narrow it down to one circuit, unless you are really unlucky and have more than one fault lol.

Edit: do you have any RCD's or RCBO's in the remote CU ?

There are no RCD's or RCBO's on the remote CU.
 
Just wondering Chris, have you been taught fault-finding techniques at all, or are you learning "as you go" ? It's very important to really understand the mechanics of your system before "probing away".
 
Just wondering Chris, have you been taught fault-finding techniques at all, or are you learning "as you go" ? It's very important to really understand the mechanics of your system before "probing away".


Am probing only on one CU (of which I know the person and he is not in the property as of yet. So getting used to the tester I have. Was used to a megger tester a few years ago (not for long though).

I have a metrel tester at the moment. So getting used to it.
 
Am probing only on one CU (of which I know the person and he is not in the property as of yet. So getting used to the tester I have. Was used to a megger tester a few years ago (not for long though).

I have a metrel tester at the moment. So getting used to it.

I can appreciate the fact that some testers take a bit of getting used to. That is a bit different to understanding how to test, and what results to expect. Just wondered what your training entailed.
 

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