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

 

[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.