How to test a circuits in steel conduit as the cpc

[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.