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Minimum IR values

OCB99

Hi everyone, 

First time poster so try and take it easy on me Grin

been looking at threads on this forum for quite a while now and it’s been a great help during my training so thanks everyone.

Just wanted to know your opinions on IR testing and how to apply the minimum value stated in BS7671. The regs state that the values in table 64 applies to a distribution circuit with all final circuits connected. Would that mean if on an EICR for example there were 10 circuits each measuring 9Mohms between two conductors (Very unlikely I know) it would be a fail as the total resistance for 10 circuit would be theoretically 0.9Mohm?

Also would this apply to simple installations where the consumer unit is directly connected to the origin, essentially classing the DNO cable as a ‘distribution circuit’.

Thanks in advance.

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  • OCB99, you will note that the minimum stipulation is in chapter 64 which is concerned with initial verification. The test at that stage is concerned with the fixed wiring only and should not include the equipment connected to it. One needs to be particularly opportune to be able to perform such a test during the erection of an installation. For EICR, it is almost impossible to exclude connected equipment in even simple installations. With respect to periodic inspection and testing, one might take the view that if it is felt IR tests are worth a punt, a good result is likely good but a poor result is not necessarily bad. 
    I have a TPN board in the training centre. A number of circuits have RCBOs with the loss of neutral white leads. TNCS system. The board serves the workshop area. Global tests conducted by me reveal 0Mohms and nearly every individual circuit indicates very low levels. Strange really because the EICR conducted several months ago indicated +999Mohms for every circuit! Time we acknowledged IR tests are of limited value for EICR rather than have fellas  fabricate results such that the veracity of the whole report is called into question!

  • in reply to lyledunn
    lyledunn said:
    you will note that the minimum stipulation is in chapter 64 which is concerned with initial verification

    That is a good point, but a whole board IR test seems to be at odds with the requirement in 641.1 to I&T during erection. Would you not do your dead tests before connecting a final circuit at its DB?

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  • in reply to lyledunn
    lyledunn said:
    you will note that the minimum stipulation is in chapter 64 which is concerned with initial verification

    That is a good point, but a whole board IR test seems to be at odds with the requirement in 641.1 to I&T during erection. Would you not do your dead tests before connecting a final circuit at its DB?

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