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?

 

[John Matrix]

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?

What you do is rewire the circuit or design it better. Or use a B type MCB but only if the circuit is adequate for a B type MCB. If it’s a Condition report surely it’s a C2 if a circuit fails max Permissible Zs. I fail to see your point anyway because a circuit can still fail doing a Zs test. We shouldn’t be relying on parallel paths to get circuits to pass. Even thow it is done, doesn’t make it right.

 

[Deleted member 26818]

How can say the circuit has failed max Permissible Zs if you’ve only calculated the Zs?
You’ve just admitted that Zs can be affected by parallel paths, so unless you measure the Zs, you cannot say whether the circuit fails or not.
There’s no prohibition in BS7671 against using parallel paths.

 

[John Matrix]

How can say the circuit has failed max Permissible Zs if you’ve only calculated the Zs?
You’ve just admitted that Zs can be affected by parallel paths, so unless you measure the Zs, you cannot say whether the circuit fails or not.
There’s no prohibition in BS7671 against using parallel paths.

You do the R1 +R2 + Ze and if it fails that then you measure Zs to see if that passes. I didn’t say never do a Zs, my point was to reduce the amount of live testing and also more importantly never calculate your R1+R2. If you calculate your R1 +R2 your calculating it from a measured Zs that could be affected by parallel paths. So it’s not a true R1+R2 reading. Only a measured R1 +R2 is a true reading.

 

[westward10]

Didn't we have this all last week.

 

[freddo]

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.

A ductor tester should be used to check the condition of the conduit joints. Test current of 100A should be fine.

 

[westward10]

Calculated Zs on an EICR - https://www.electriciansforums.co.uk/threads/calculated-zs-on-an-eicr.172137/page-4#post-1510423

 

[John Matrix]

My mate would just stick it on an RCBO and run if it failed lol. The rough arse

 

[Toneyz]

So how do you do an R2.

With a wandering earth lead. If I explain any further I feel that I am teaching you to suck eggs.

 

[John Matrix]

With a wandering earth lead. If I explain any further I feel that I am teaching you to suck eggs.

I’ve had that feeling every time I’ve replied to a comment lol. On a serious note I feel that some people who are doing EICRs are not clued up enough to be doing them. But I’m happy to help anyone out. We all have to learn and help each other out. Two heads are better than one.

 

[westward10]

My wander lead is tying up a load of conduit in the van.

 

[Toneyz]

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?

Then either the design is wrong or it has not been constructed to the design. A parallel path can be out of the control of the designer and in practice, this could disappear by a plumber inserting a plastic Tee in a copper pipe.

 

[westward10]

It was perfectly acceptable in the 16th Ed to deliberately put in place parallel paths through supplementary bonding to reduce fault path impedance so it is not impossible to discover this doing an EICR.

 

[spark 68]

Supplementary Bonding is still valid in the 18th, see reg group 544.2

 

[westward10]

Supplementary Bonding is still valid in the 18th, see reg group 544.2

Not to deliberately reduce values of Zs that was removed under Amendment 2 of the 16th Ed.

 

[spark 68]

In the 17th GN8 amd3 (which is the last GN series I currently have) it gives reg 411.3.2.6 and states "Supplementary bonding is required by BS7671 to be provided in the following circumstances: where, in the event of an Earth fault, the conditions for automatic disconnection cannot be fulfilled in the time required by reg 411.3.2.2, 411.3.2.3 or 411.3.2.4, as appropriate"

The other circumstances listed are in special locations such as bathrooms etc,,, etc.

This sure looks like reducing the Zs to me

 

[ipf]

I’ve had that feeling every time I’ve replied to a comment lol. On a serious note I feel that some people who are doing EICRs are not clued up enough to be doing them.

When you've had that feeling as often as I have, over the years, I might take you seriously.

As regards your serious note....I totally agree.

 

[spark 68]

Just out of (genuine) interest Westy can you give me the reg number for the 16th where SB was not allowed to reduce a Zs ?, I still have regs books and some OSGs going back to the 15th ed and I will look it up.

The special locations bit in my previous post, which I never bothered writing out is more to do with reducing Ut (touch voltages) which is a different kettle of fish entirely.

 

[Deleted member 26818]

Although 413-02-15 was deleted in 16th edition Amd. 2,
413-02-04 (i) still allowed it to be used with similar wording to that of 17th edition 411.3.2.6.

 

[Ian1981]

Section 419 deals with achieving fault protection through the likes of supplementry bonding if ADS can’t be achieved by 411.3.2

 

[spark 68]

Cheers, Spin, I have the earlier 16th ed regs books and the last brown book (2004) of that edition and I will if I can be bothered look that up.

 

[spark 68]

So Ian, are you saying in effect that SB can be used to lower a Zs to achieve disconnection times ?, I do have the 18th regs book but I am just being lazy

I don't have the 18th GNs yet, but I am considering getting them

 

[westward10]

Cheers, Spin, I have the earlier 16th ed regs books and the last brown book (2004) of that edition and I will if I can be bothered look that up.

See what it said prior to amendment 2 as mine is in the loft.

 

[westward10]

Section 419 deals with achieving fault protection through the likes of supplementry bonding if ADS can’t be achieved by 411.3.2

Is this with intent of reducing Zs or a measure to reduce danger to exposed parts.

 

[Ian1981]

So Ian, are you saying in effect that SB can be used to lower a Zs to achieve disconnection times ?, I do have the 18th regs book but I am just being lazy

Supplementary bonding to the location between accessible exposed conductive parts and extraneous parts and circuits is one method.
Another more commonly used method is Rcd protection

 

[Ian1981]

Is this with intent of reducing Zs or a measure to reduce danger to exposed parts.

To limit the touch voltage to below 50 v

 

[westward10]

To limit the touch voltage to below 50 v

This is my view.

 

[Ian1981]

This is my view.

Yes I do see your point.
My explanation of section 419 could have been clearer

 

[westward10]

You are always clear Ian tis my mind that isn't, all that tinnitus.

 

[spark 68]

There are basically two reasons for SB, the special locations part is to do with reducing Ut to keep it below 50V, medical locations below 25V, back in the 16th agricultural locations required Ut below 25V as well I recall, but I don't recall now which specific amd, or if it ever changed in that entire edition.
The other part is to achieve disconnection times and was to reduce Zs by default, the regs are worded --- backward in a lot of cases.

 

[westward10]

Find your early 16th and see what is says.