Testing Questions - help.

[chrisgc]

1) So should the Circuit Breakers be in the off/open position or the on/closed?


2) The remote (outbuilding) CU comes from a 'way' in the main CU (located in the house), and turning main switch off on the remote CU makes the IR test (which was being done on a cooker circuit) a PASS.

If what you say means that there is a fault in the outbuilding are you able to suggest some possible things I can do to narrow down the possible problem?

 

[Strima]

Test the individual circuits on the second DB, without seeing it there's no way of diagnosing a fault.

Description of circuits, fixing methods, attached equipment etc would be a start.

 

[chrisgc]

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?

 

[Guitarist]

The Failed N-E IR test reading I was getting was because the outbuilding has a small consumer unit inside powering lights and switches.

The main switch of this outbuilding CU was on/closed but when I opened the switch (turned main switch off) the N-E reading was fine.

This is an existing installation that I am practising testing on.

Also one question with regards to IR testing and OSG:

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?

Time to get the latest OSG methinks

 

[chrisgc]

Time to get the latest OSG methinks

I know lol - have they updated their picture then on the IR test or is it still the same as the red one?

 

[Guitarist]

I know lol - have they updated their picture then on the IR test or is it still the same as the red one?

It's not always about pictures, you do realise?

 

[spark 68]

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.

 

[Richard Burns]

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.

 

[chrisgc]

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.​

 

[spark 68]

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.

 

[chrisgc]

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)???

 

[spark 68]

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.

 

[chrisgc]

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)?

 

[spark 68]

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.

 

[chrisgc]

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).