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Discuss 2391-51 Online Exam in the Electrical Courses and Electrical NVQ's area at ElectriciansForums.net

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Hello everyone,

I'm looking for any advice at all on passing this online exam.

I have completed everything else without any problems including the 2391-50 but have failed this one three times now and twice only one question away.

I am not an electrician so probably found it harder than most (I was an electrician's mate for about 6 years) and my job involves security electronics. I put myself through this course to take on RCD testing alongside my own job.
The college course requirements was basic electrical knowledge but this is far from it, and the course wasn't really taught as it was assumed you would already know or get from GN3.

I have just failed on "understand the requirements for testing electrical installations during periodic inspection and test, and scraped through understand the requirements for the periodic inspection of an electrical installation.

The one question that pops up is "what would the expected resistance be of 10mm CPC at a length of 20 metres at 20c the answer I get is nowhere near any of the multiple choice answers so any explanation of how to do this would be much appreciated. This was part of the course work that was not delivered to us.

I have found some of the questions are tricky as the answers could possibly be one or the other!

Any advice at all would be appreciated guys!

Thanks,

Raymond
 

darkwood

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Hi... before we help you out can you show your calculations, as a forum we do not give direct answers to exam questions or projects but we are all too happy to show you where you are going wrong in your calculations ... if you can also list the answers provided as it has been known that they are incorrect in themselves.
 
Hello everyone,

I'm looking for any advice at all on passing this online exam.

I have completed everything else without any problems including the 2391-50 but have failed this one three times now and twice only one question away.

I am not an electrician so probably found it harder than most (I was an electrician's mate for about 6 years) and my job involves security electronics. I put myself through this course to take on RCD testing alongside my own job.
The college course requirements was basic electrical knowledge but this is far from it, and the course wasn't really taught as it was assumed you would already know or get from GN3.

I have just failed on "understand the requirements for testing electrical installations during periodic inspection and test, and scraped through understand the requirements for the periodic inspection of an electrical installation.

The one question that pops up is "what would the expected resistance be of 10mm CPC at a length of 20 metres at 20c the answer I get is nowhere near any of the multiple choice answers so any explanation of how to do this would be much appreciated. This was part of the course work that was not delivered to us.

I have found some of the questions are tricky as the answers could possibly be one or the other!

Any advice at all would be appreciated guys!

Thanks,

Raymond
Sorry but if you are not an Electrician why are you doing a Inspection and Testing course? Is it for the knowledge as a supervisor, or are you intending to carry out testing as part of your job.
 
He has the info apart from one detail, the milli ohm/m of the conductor. Know that you can find the answer by simple calculation.
 
  • Thread Starter Thread Starter
  • #6
Hi... before we help you out can you show your calculations, as a forum we do not give direct answers to exam questions or projects but we are all too happy to show you where you are going wrong in your calculations ... if you can also list the answers provided as it has been known that they are incorrect in themselves.
Thanks for offering to help Darkwood. I don't have the answers that was on the multiple choice but here is my calculations and the answer I got for the above question. As you can see I am going wrong somewhere as that is too low. I was never taught how to calculate it, so thanks in advance for your help, I really appreciate it.
Post automatically merged:

Sorry but if you are not an Electrician why are you doing a Inspection and Testing course? Is it for the knowledge as a supervisor, or are you intending to carry out testing as part of your job.
Our department was merged with the electrical squad to cut down on managers in our company. There was an opportunity to carry out RCD testing alongside my own role, which would come with a salary increase and job security so decided to go for it.
 

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  • #12
Where has the 10 come from in your calculation.
Do you have a list of the actual answer options.
I don't have the answer options, I don't think I would be allowed to write them down and take out the test. The 10 was the CSA of the conductor. I'm going by the formula in GN3 R=mΩ/m X L and divided by 1000 so 3.66Ω / 10 x 20 divided by 1000 = 0.00732
 
Your 3.66 is 2 × 10mm you need a single conductor (1.83) recheck the Table. The csa of 10mm is not relevant in the calculation. You need the length and resistance of the single conductor (1.83) × length then convert to ohms by ÷ 1000. You are nearly there.
 
  • Thread Starter Thread Starter
  • #14
Your 3.66 is 2 × 10mm you need a single conductor (1.83) recheck the Table. The csa of 10mm is not relevant in the calculation. You need the length and resistance of the single conductor (1.83) × length then convert to ohms by ÷ 1000. You are nearly there.
Thanks very much for your help westward - your a star!
 

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