best practice continuity

[sambotc]

Sorry i've re-read my original post and I didn't add enough detail to the circuit, it was a 3 phase isolator and there was nothing connected to it. No CPC other than the enclosure, and armour to disconnect. I would have had to have made a link to carry the test out.

I carried out R1R2 on other lighting radials so that they could see I was aware of the technique used. When he questioned why I hadn't written down the R1R2 test method on the right up, i explained and was told you should always perform R1R2 as the result will be different than the calculated R1 + R2.

I made a decision as I would expect to in a similar situation or scenario in the real world, and felt a bit peeved. I get a bit tired of doing these kind of assessments and being judged on what they want you to do (without telling you) rather than accepting that you have used a bit of common sense and assessed the situation rather than follow the book.

That is unless I am missing something which I will gladly hold my hand up to if it is the case?

 

[robsparky1975]

When you do the 2391 test follow to the book,this will make your chances of passing improved,will can all aplly common sense but the exam situations are not made this way so follow GN3 and you can not go wrong,besides its good practise to use the R1+R2 method as said earlier to prove polarity,even if its making you fed up for having to do a link or such like,its getting through the exam and passing it that counts.They want to see competence in testing,if done so pass is easy.

 

[Amp David]

Another query I have is whats a calculated r1 r2 reading?

Are you measuring the length of the circuit then using the values given in regs for the resistance of said cable to achieve this?

 

[spark 68]

As Rob sparky said do it to the book in the exam as this is what they are expecting.

When I did mine I had to do an IR test on a TP+N+E cable, and because I did not have enough links I had to do all 10 tests, a bit tedious to say the least, I would have done this differently in the field, but as it was under exam conditions this was what I had to do.

 

[sambotc]

Another query I have is whats a calculated r1 r2 reading?

Are you measuring the length of the circuit then using the values given in regs for the resistance of said cable to achieve this?

No, measuring R1, Rn and R2 then adding R1 to R2 together.

 

[Amp David]

Ah I see.

 

[spark 68]

The thing is with the 2391, they are so pedantic, both with the written and the practical, it is better not to deviate in any way if you want to pass.

@ To the OP, so did they fail you because of this ?, if you don't mind me asking.

 

[sambotc]

Nah no fail, not sure if you can fail it? The bloke walked off and left me to it!

It was only when he was looking over the write up and questioned the no R1R2 etc etc

I asked the question for real life purposes not the exam, I know you have to do what they want to see unfortunately, but the assessor was leading me to believe it should be done on site as well, and that R1,Rn and R2 was somehow inferior, which is why I posted originally.

 

[spark 68]

Just to clarify, which course are you doing ?, because they can and do fail candidates on the 2391.

I asked the question for real life purposes not the exam

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I don't really see the need to do the R1+R2 as seperate measurements in real life either for all of the reasons already said, mainly because you cover 3 items with one test, and quicker is better, as well as more convenient.
But I don't actually see what is wrong with measuring them seperately and adding the results together either, other than you will have more testing steps to do.

In fact GN3 states other testing methods are not precluded, so long as the same end results are obtained.

However on courses it is better to just do it by the book as we have already said, and not 'rock the boat' so to speak.

 

[sambotc]

Its the EAL diploma testing and inspection, equivalent to C&G 2391 so I was led to believe, they just use EAL as the certification body. Got my written test paper on the 26th.

Yeah don't get me wrong I wasn't sat there arguing my point with him, I saved that for here lol I just questioned the logic as I was more interested in making sure I hadn't missed something obvious regarding the benefit of R1R2.

As i've said, in a real world scenario where the cable length was longer than my test leads, i'd combine as it makes sense, just effectively using the line conductor as a wander lead whilst also checking polarity and R1 continuity at the same time, but if it were a situation like the board where you could reach with the leads end to end, I don't see why you would want to disconnect conductors etc when it could be carried out without having too.

 

[dagrat]

I think testing r1+r2 is by far the more efficient method than testing separately, as has already been stated. However you appear to have an excellent understanding of the requirement for the test so I'd be very surprised if on this practical the assessor would mark you down for this.
In real life the benefits of the combined test would provide more results in one step, although the specific test result would be the same

 

[Guitarist]

Another query I have is whats a calculated r1 r2 reading?

Are you measuring the length of the circuit then using the values given in regs for the resistance of said cable to achieve this?

You could calculate the r1+r2 in this way for checking purposes. Rarely used though as it's hard to know exactly how long your circuit is unless measured out during installation.

 

[dagrat]

Actually the table for resistance of copper conductors can give a reasonably accurate measurement of length of Cable and r1+r2, but not the first choice method as per previous posts

 

[robsparky1975]

So if you pass this exam i hope that you would get a City & guilds 2391 certificate,would the eal have 2391 written on it,only saying this as agency donks for instance only know certain quals i.e 2391,2382 etc.

 

[Rob Smith 643]

I'm relatively new to inspection and testing but not to installation. Its a hard road but an interesting one and the forum does help. I'm confident with my inspection and testing procedures and know the tester inside out as it were. I often get perplexed by results even when they are well within tolerance/guidelines/tables etc, particularly when the measured values don't mirror the calculated/expected values. Some would say why care but I'm a bugger for needing to understand why. Most dwellings I have 'I & T'd' during installation and upon completion give Ze readings in the region of 0.12 to 0.17. On my last lighting install the highest measured R1+R2 was 1.79 (landing light fitting) however the Zs taken at this lighting point was 1.09. This gives me a calculated value of 1.91 versus a measured value of 1.09. This is not the first time and I doubt it will be the last but I would be obliged for some theoretical, experienced based explanations to help me understand. Cheers, Rob.