2 X 10mm earths

[sparky999]

Been to a friends house tonight to look at a problem light fitting, they recentley had their ccu upgrade to a dual board by a local company, looking in the cupboard to isolate the supply i noticed the meter arrangement and they have taken two 10mm earths from the tncs supply to the ccu. Is this acceptable as it equals to 20mm or should it of been 16mm?

 

[spinlondon]

I think the adiabatic equation is raising it's ugly little head again.

 

[Riggy]

Why would it not be?

 

[M107]

20mm will be ok 999

just two 10 milly in parallel.

 

[ianmacd]

Agreed. It is fine as long as both are labelled independently with do not remove notices.

 

[Manator]

In general it will be ok, the problem arises when and if one becomes disconnected, again the adiabatic equation could be used to verify any problem should this happen. I have seen similar parralel runs of earthing where an upgrade to bonding has been made.

 

[Andy™]

In general it will be ok, the problem arises when and if one becomes disconnected

more failsafe than one and that single one being disconnected

 

[ianmacd]

What about the - 'There is only one such 'Earthing Conductor' in each installation' - statement.Don't know the Reg No. off hand - but GN8, Pg 21 3.1;\ ; \

It is 1 parallel conductor

 

[Andy™]

nothing wrong with cables in parallel.

 

[Evans Electric]

These things occur, board change, ooops no 16mm on the van , its Saturday aft. and every one is shut, but I reckon 2 X 10mm will do the job just as well .

Well I agree . Now we will get the ..."But you must go back with some 16mm next week"

 

[ringer]

My questions would be along the lines of:- Are the terminations acceptable? Do they share a termination? Are both 10mm cables securely clamped in the terminations at both ends? Is there a possibility one cable may become detatched?

 

[spinlondon]

My first question would be, is this an earthing conductor or in fact a bonding conductor?

Does it connect the MET to the neutral of the source of energy, or is it connecting the earth bar in the CU to the MET?

 

[spinlondon]

I suppose that if the conductors are being used to connect exposed-conductive-parts of equipment to the MET, then they could well be considered to be CPCs, or perhaps even supplementary bonding conductors?

Then again, if the conductors are being used to provide equipotential bonding then they would be protective bonding conductors.

Perhaps one is a CPC, and the other is a bonding conductor?

 

[Chr!s]

In a tncs a earthing conductor is combined with the function of a bonding conductor, also theres nothing wrong with a combined cpc and bonding conductor

 

[Evans Electric]

Where the hell is this thread going ? Its 2 X 10mm instead of a 16mm !!! you'd think it was the end of the world !!! Its not bonding either its the main earth doubled up, its not quite correct but it does the job FFS . Bound to upset all the assessors........OMG !! ...can't find that in "The Book" , Well wellcome to the real world . Have a look in some of the industrial premises if you're fretting about 2 X 10mms serving as a 16mm. Bloody hell whats the matter with everyone, bloody well picking flies, perfect world , everything to the book , argue black is bloody blue sometimes.

 

[Sidewinder]

Nah Deke,

Some will argue black is white!

I once was given a written mathematical proof that electricity did not run down cables that it was transmitted by electro magnetic waves from point to point, the maths was so complex very few people could find the "deliberate" error, if it was there...

 

[Evans Electric]

Was it similar to the aeronautical scientists studying how bees fly , and given the weight to wing ratio etc it was proven , on paper, that a bee cannot fly. Don't you just love it.

 

[Sidewinder]

I have no blinking idea mate, I've slept since then it was by my electromagnetics prof at uni!

Yes I was sober for that lecture I drove there & back!!!

 

[PC Electrics]

It's by analysing stuff we don't understand that pushes forward the boundaries of science and engineering. That's what happens in the "bumble bee" scenario. Things like this show that our scientific understanding is incomplete. Further analysis and study can then be used to clear up those issues.

If you conducted a Design FMEA on the earth conductor then one failure mode would be "becomes loose and detached" with the effect being that the installation is now unsafe.

One way to design out this failure mode might be to have two conductors. The chances of both becoming detached at the same time would be very much smaller than with one. Inspection should find the fault whilst the installation remains 'safe'.

 

[Sidewinder]

FMEA's can be a wonderful thing!

It is a different way of thinking sometimes!