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

 

[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