IR testing on new build

[Buzz1980]

Hi all testing of new build house. When carrying out IR testing on circuits unplugged all equipment and took down smoke alarms. As there was a lot of lights connected with lamps and installed in twin and earth. I put live and neutral together and tested to Earth. IR test was starting off low but eventually got above 200mega ohm. So recorded that but got me thinking will the fact that the surge protector was still connected that will make the readings go all over the place. Every circuit got above 200mega ohm which I was happy about but would this surge protector affect readings ? Also find a lot of sparks very rarely carry out IR tests just rely on RCBOs or RCDs ? Hope use can help

 

[telectrix]

new build - possible damp. applying 500V IR test tends to dry the circuit and readings increase the longer you leave the 500V applied. surge protectors in the CU should not affect, as you circuit/s are not connected to it.

 

[davesparks]

You should be carrying out L - N tests for initial verification, not just L+N - E
I assume this is initial verification as you say new build?

The slow rise in IR can be due to dampness from the plaster and/or capacitance of the cables.

If you have disconnected L and N to do the test then the SPD won't be in the test circuit.

 

[telectrix]

You should be carrying out L - N tests for initial verification

agreed, but maybe he was called in to test after lamps had been fitted. bad project management.

 

[pc1966]

Also find a lot of sparks very rarely carry out IR tests just rely on RCBOs or RCDs ?

You mean the "bang! test" approach?

You might want to read the fatal accident inquiry report that I quoted in 2nd part of this post:

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[davesparks]

You should be carrying out L - N tests for initial verification

agreed, but maybe he was called in to test after lamps had been fitted. bad project management.

Maybe he was, but it still doesnt excuse not carrying out the correct sequence of tests.

 

[Buzz1980]

Cheers lads, yeah that’s right called in afterwards when all lights have been fitted bollards lights, spot lights, fans. So thought a LN joined down to earth would be best option since they will be touching earth in a twin earth cable ?

 

[pc1966]

If there are non-removable loads already fitted (e.g. LED lights) then L+N -> E is your only real option, and it is the most important safety aspect.

SPD tend to show a constant low IR value (well below 1M) at 500V, but if you re-test at 250V then they are in to the several-tens of M ohm region.

In fact quite a lot of SPD show that for L-N using a MOV type of protection, but N-E can be a GDT and sometimes they still look open at 500V (but would show M ohm or less, and sometimes a worrying squealing, if tested at 1000V)

 

[Wilko]

Hi - just my opinion, but for EIC of a new circuit you must perform the dead tests with no loads connected, sorry if that is inconvenient for Mr Builder.

 

[Ian1981]

Regulation 643.3.1 does allow the testing of the line and neutral conductors connected together and to the earthing arrangement where appropriate, this falls under chapter 64 which is initial verification and not periodic inspection and testing so it is applicable.
This is also echoed in GN3 for circuits vulnerable to this test.
So it’s down to your determination of what is and what is not appropriate.

 

[Buzz1980]

Cheers lads for the replies. TBH i would prefer to do L-N , N-E,L-E IR testing but with all these loads connected would take more than half the day to disconnect everything. Then to put all together again, so tested at LN joined to earth getting over 200mega ohms. I have seen sparks just carry out R1+R2s and Then live testing. Where I like to carry out IR testing even though everything on RCDs these days.

 

[Ian1981]

The simple answer is that the test should have been carried out prior to the loads being fitted in circuit.

 

[davesparks]

Cheers lads for the replies. TBH i would prefer to do L-N , N-E,L-E IR testing but with all these loads connected would take more than half the day to disconnect everything. Then to put all together again, so tested at LN joined to earth getting over 200mega ohms. I have seen sparks just carry out R1+R2s and Then live testing. Where I like to carry out IR testing even though everything on RCDs these days.

Firstly test before loads are connected, connecting lights via plugs and sockets where possible helps this.

Then they are not complying with the regulations, RCDs do not negate the need for RCD testing.

There seems to be this attitude/opinion among a lot of 'sparks' that RCD are some kind of magical device that cure all problems and prevent electric shocks from occurring.

 

[richy3333]

IR testing isn't an option its part of initial verification and should be done with no loads connected - as @davesparks said.

GN3 at 2.6.7 states that 'all lamps be removed and fluorescent and other discharge luminaries and other equipment disconnected. Where the removal of lamps and/or disconnection of current using equipment is impracticable, the local switches controlling such lamps and/or equipment should be open. An insulation resistance test of L&N connected to earth will ensure that all circuit protective conductors are tested'. In my mind that is a process to use sparingly and as a last result not a continuous get out to proper and complete IR testing?

 

[radiohead]

In the real world, on site, it is often not practical for a L-N test to be carried out as part of the initial verification, it simply doesn't work that way and IMO a LN-E test is compliant and adequate. I don't expect everyone to agree but I am absolutely certain that many of those who claim to always do L-N tests on lighting circuits are talking out of their arsenals. In many cases it would be necessary to provide temporary joints at each lighting point, test and then disconnect the temps before connecting the fittings proper.
Where flat T/E is used the chance of a low IR between live conductors is miniscule....because there is a bare uninsulated cpc sandwiched between, any breakdown in insulation is invariably going to show on the cpc, not between live conductors.