How to test a circuits in steel conduit as the cpc

[Questforknowledge]

Good evening

I am currently a training to become an electrician. I do hold both initial verification and periodic testing qualifications however this is an issue I have never personally had to deal with and was never mentioned on any of my courses as often seems to be the case.

Basically I am wondering how you would hypothetically go about testing either a ring or radial circuit if you didn't have a seperate cpc but the conduit itself acted as this.

Look forward to hopefully getting a response and some clarity

Regards Harry

 

[Deleted member 105166]

Reg. 543.2.2 and 543.2.5. Treat it as you would any other CPC for testing.

 

[Questforknowledge]

Reg. 543.2.2 and 543.2.5. Treat it as you would any other CPC for testing.

So with regards to the testing how would you gain and end to end reading for r2 and after that an R1+R2?. I understand I could opt for an R2 reading instead of R1 +R2

 

[Deleted member 105166]

You could either use a wander lead or link the conduit to the line conductor with croc clips (or banana plug to croc clip with an R2 adaptor) for R1+R2

 

[westward10]

For a radial circuit you can calculate R2. If you measure the continuity of the line and neutral then divide in half this will give you R1 assuming the line and neutral are of the same length. Then measure R1 + R2 and deduct your first reading which should give you an approximate R2. For a ring final circuit you cannot do an r2 for the cpc as you have no end to end as such but you can use the same principle to to calculate R2 from the farthest point.

 

[Toneyz]

R2 being the CPC I don't think you should be calculating it.

 

[westward10]

R2 being the CPC I don't think you should be calculating it.

There is nothing wrong with my suggestion, you are using various measurements and using some calculations to extract R2. Using a wander lead and subtracting the leads resistance is no different as this is also a calculation.

 

[ipf]

Wander lead and measure for R2. On the results, fill in R2 rather than r2 and R1+R2. On the schedule, 'cont' (containment) for cpc.

 

[Questforknowledge]

Wander lead and measure for R2. On the results, fill in R2 rather than r2 and R1+R2. On the schedule, 'cont' (containment) for cpc.

Thanks for that much appreciated

 

[PEG]

Hi,and don't forget to do the inspection part,as,if containment is effectively,a CPC, with possibly dozens of "connections",it may pass the testing,but could give a visible indication,of not being capable of sustaining a higher,fault current.

 

[John Matrix]

There is nothing wrong with my suggestion, you are using various measurements and using some calculations to extract R2. Using a wander lead and subtracting the leads resistance is no different as this is also a calculation.

You should never calculate R1 +R2. Or R2 But you can calculate your ZS. This is what the NIC have told me is acceptable

 

[westward10]

You should never calculate R1 +R2. Or R2 But you can calculate your ZS. This is what the NIC have told me is acceptable

How do you measure R2 with no calculation. Your own method not how the NIC think it should be done.

 

[Ian1981]

You should never calculate R1 +R2. Or R2 But you can calculate your ZS. This is what the NIC have told me is acceptable

During the design stage it is very much acceptable to calculate R1+R2 and necessary in most of, if not all cases

 

[John Matrix]

During the design stage it is very much acceptable to calculate R1+R2 and necessary in most of, if not all cases

I’m not talking about the design stage. I’m talking about testing on site. We should be avoiding live testing whenever possible. And doing an R1+R2 test. Then calculate the ZS. Not always possible I know but the NIC I believe are trying to get this pushed forward because people are working live on steps trying to do a ZS and having accidents

 

[westward10]

So how do you do an R2.

 

[John Matrix]

How do you measure R2 with no calculation. Your own method not how the NIC think it should be done.

What calculation would you need to do to perform an R2 test? You need to Null the wandering lead first if that’s what your referring to?

 

[John Matrix]

How do you measure R2 with no calculation. Your own method not how the NIC think it should be done.

What calculation would you need to do to perform an R2 test? You need to Null the wandering lead first if that’s what your referring to?

During the design stage it is very much acceptable to calculate R1+R2 and necessary in most of, if not all cases

also I personally think that a measured R1 +R2 test gives a more true reading than a ZS because a Zs is influenced by potential parallel paths that will lower the reading. And as we know parallel paths can be removed. If this occurred the ZS could potentially raise above the acceptable level for the circuit/ protective Device.

 

[Ian1981]

What calculation would you need to do to perform an R2 test? You need to Null the wandering lead first if that’s what your referring to?

also I personally think that a measured R1 +R2 test gives a more true reading than a ZS because a Zs is influenced by potential parallel paths that will lower the reading. And as we know parallel paths can be removed. If this occurred the ZS could potentially raise above the acceptable level for the circuit/ protective Device.

Parallel paths will in most cases result in a lower result of zs than the calculation of zs=ze+(R1+R2) rather than a higher value

 

[John Matrix]

Parallel paths will in most cases result in a lower result of zs than the calculation of zs=ze+(R1+R2) rather than a higher value

That’s what I was getting at in my comment. I’m so many words.

 

[Deleted member 26818]

Problem here, is that we work to BS7671, not to the NICEIC regulations.
There are no tables of maximum R1+R2 in BS7671, there are only tables for maximum Zs.
So it’s all very well measuring R1+R2 and adding it to Ze, but what do you do if that value is above the maximum permissible?