A BIT OF A PUZZLER !!

[steptoe]

Im still confused as to what is bonded where.

and, Im still of the opinion that if you are extending the EZ and are aware of the hazards etc and are willing to understand and limit them then you still need an EARTHING CONDUCTOR to the garage CU from the MET.

---------- Post Auto-Merged at 22:51 ---------- Previous post was made at 22:50 ----------

Yes but bonds to the gas as it goes out the house to the garage then to the garage CU Met.

the garage cu does not have an MET if you are extending the EZ.

 

[sparkytim]

Yes but bonds to the gas as it goes out the house to the garage then to the garage CU Met.

Then that sounds ok see the article below

http://www.theiet.org/publishing/wiring-regulations/mag/2005/16-elect-inst-outdoors.cfm

 

[apprentice87]

Hi all, First off, i would have thought by now that everyone would have got used to the idea that it is PERFECTLY ACCEPTABLE to export PME earths. No good arguing with me, take it up with the IEE or the electrical safety council if you disagree, it is their considered opinion not mine!!!!

Anyway, Plumber is exactly right; just because the CSA of a SWA cable meets the THERMAL constraints that allow it to be used as a cpc, does not mean that it meets the conductivity requirements to be equivalent to a 10mm copper conductor that would be required for a PME bond. [That is, assuming your incoming supply neutral is 35mm or less] To do this would require an armouring CSA of about 80mm, so you would be looking at a very large cable!!

Further, as Plumber also points out, there are other issues involved with using the armour [or an internal core] of a cable as a PME bond. This is because of the extra heating effect of such use on the cable concerned. You CAN use an internal core or the armour [if the CSA is large enough] PROVIDED the cable is only lightly loaded, This is where your judgement comes in!!! What would you call "lightly loaded" Personally, and this is only me [and I have not passed my 17th ed yet!] i would have thought that as the heat in a cable is a function of the current squared, that calculating the current that gives out say, half the heat of a fully loaded cable, [and no, this is not just a question of halfing the original current!] one would produce a cable that would count as "lightly loaded" As i say though, this is just the way i see things, others may take a different view!!!!!

In the event that the armour is not of a sufficient CSA to act as the bonding conductor, you are not allowed to "top it up" as it were by adding a separate smaller cable in parallel. Obviously, any separate cable you do add will be in parallel to the armour, but, the additional cable MUST of itself be large enough to act as the bonding conductor on its own, without any help from the armour. This is because due to various magnetic effects, the like of which are beyond me, it is impossible to predict how the fault current would be shared between the two [not just a case of Ohms law apparently]

Finally the size of bond required in a PME system is determined by the size of the incoming neutral of the supply. That does not mean the size of the conductor in your swa, or the size of you meter tails either, but the size of the neutral in your service cable..

Hope all this helps or is at least interesting!!

john..

 

[steptoe]

Hi all, First off, i would have thought by now that everyone would have got used to the idea that it is PERFECTLY ACCEPTABLE to export PME earths. No good arguing with me, take it up with the IEE or the electrical safety council if you disagree, it is their considered opinion not mine!!!!Anyway, Plumber is exactly right; just because the CSA of a SWA cable meets the THERMAL constraints that allow it to be used as a cpc, does not mean that it meets the conductivity requirements to be equivalent to a 10mm copper conductor that would be required for a PME bond. [That is, assuming your incoming supply neutral is 35mm or less] To do this would require an armouring CSA of about 80mm, so you would be looking at a very large cable!!

Further, as Plumber also points out, there are other issues involved with using the armour [or an internal core] of a cable as a PME bond. This is because of the extra heating effect of such use on the cable concerned. You CAN use an internal core or the armour [if the CSA is large enough] PROVIDED the cable is only lightly loaded, This is where your judgement comes in!!! What would you call "lightly loaded" Personally, and this is only me [and I have not passed my 17th ed yet!] i would have thought that as the heat in a cable is a function of the current squared, that calculating the current that gives out say, half the heat of a fully loaded cable, [and no, this is not just a question of halfing the original current!] one would produce a cable that would count as "lightly loaded" As i say though, this is just the way i see things, others may take a different view!!!!!

In the event that the armour is not of a sufficient CSA to act as the bonding conductor, you are not allowed to "top it up" as it were by adding a separate smaller cable in parallel. Obviously, any separate cable you do add will be in parallel to the armour, but, the additional cable MUST of itself be large enough to act as the bonding conductor on its own, without any help from the armour. This is because due to various magnetic effects, the like of which are beyond me, it is impossible to predict how the fault current would be shared between the two [not just a case of Ohms law apparently]

Finally the size of bond required in a PME system is determined by the size of the incoming neutral of the supply. That does not mean the size of the conductor in your swa, or the size of you meter tails either, but the size of the neutral in your service cable..

Hope all this helps or is at least interesting!!

john..

NO it is not,

you must first obtain permission from the DNO,

so before you continue spouting please get basic facts right first,

secondly,

OP is not intending exporting PME EARTH, but is wanting to extend EZ,

get your facts right, yet again I say this to you.

thirdly, where is it prohibited to use parallel conductors as an earth? or any other conductor for that matter, in fact in some circumstances it is recommended.

fourthly,

IMO we are talking about earthing conductors, not bonds,

I really dont know if your name relates to your experience or not,

but perhaps you should read more questions than you answer.

---------- Post Auto-Merged at 01:19 ---------- Previous post was made at 01:16 ----------

Hi all, First off, i would have thought by now that everyone would have got used to the idea that it is PERFECTLY ACCEPTABLE to export PME earths. No good arguing with me, take it up with the IEE or the electrical safety council if you disagree, it is their considered opinion not mine!!!!Anyway, Plumber is exactly right; just because the CSA of a SWA cable meets the THERMAL constraints that allow it to be used as a cpc, does not mean that it meets the conductivity requirements to be equivalent to a 10mm copper conductor that would be required for a PME bond. [That is, assuming your incoming supply neutral is 35mm or less] To do this would require an armouring CSA of about 80mm, so you would be looking at a very large cable!!

Further, as Plumber also points out, there are other issues involved with using the armour [or an internal core] of a cable as a PME bond. This is because of the extra heating effect of such use on the cable concerned. You CAN use an internal core or the armour [if the CSA is large enough] PROVIDED the cable is only lightly loaded, This is where your judgement comes in!!! What would you call "lightly loaded" Personally, and this is only me [and I have not passed my 17th ed yet!] i would have thought that as the heat in a cable is a function of the current squared, that calculating the current that gives out say, half the heat of a fully loaded cable, [and no, this is not just a question of halfing the original current!] one would produce a cable that would count as "lightly loaded" As i say though, this is just the way i see things, others may take a different view!!!!!

In the event that the armour is not of a sufficient CSA to act as the bonding conductor, you are not allowed to "top it up" as it were by adding a separate smaller cable in parallel. Obviously, any separate cable you do add will be in parallel to the armour, but, the additional cable MUST of itself be large enough to act as the bonding conductor on its own, without any help from the armour. This is because due to various magnetic effects, the like of which are beyond me, it is impossible to predict how the fault current would be shared between the two [not just a case of Ohms law apparently]

Finally the size of bond required in a PME system is determined by the size of the incoming neutral of the supply. That does not mean the size of the conductor in your swa, or the size of you meter tails either, but the size of the neutral in your service cable..

Hope all this helps or is at least interesting!!

john..

I have just read this again,

and

where have you got this load of tosh from?

and I am being very polite.

 

[apprentice87]

Hi, Steptoe, first off, i just posted the bit about it being perfectly ok to export PME earths as the original poster seemed to state in his very first line that he thought that this was not permitted. Well, according to the IEE and others it is, and i think they might just know what they are on about...

I know that the question here was about earthing, but then things veered of in the direction of bonding.

I never said anything about not being able to use parallel earths, i suppose i must not have written things very clearly.

You are of course right that you are supposed to get the permission off the DNO, and if they want they can impose conditions of their own too

Finally, as to where did I get this load of

 

[Zeespark]

John, the DNO, under the ESQC Regulations have precedence over the IET/ESC, by LAW. If you phone your local DNO up and ask if you can extend a TNCS supply outside of an EZ, they may tell you that you CANNOT do this. What the IET/ESC say in this matter in the example I have just given does not stand up to legal and official scrutiny.

Andy

 

[apprentice87]

Hi Andy,

Yes it is right what you say about the DNO backed up by the ESQC regulations having precedence; and yes, the DNO can set any conditions they like, but if exporting the TNCS supply was not good, and most of all, common and accepted practice and also generally permitted by the DNO too, then presumably the ESC and the IEE/IET would not give lots of recommendations/information on how to do it properly?

I understand what you say about exporting the supply outside the EZ, but surely apart from exporting/extending the earth from the main building [which is what everyone goes on about] if you do things properly, in the way that is recommended, are you not also exporting/extending the EZ too?? does this not make it ok??

If i put up an outbuilding and wire it from my house in say, 2.5 SWA and just use the cpc in the cable to bring in the earth from the house [instead of TT'ing the shed] then yes, i can see that could, in some circumstances, be wrong, but if i do the same thing, using the house earth, and ALSO [in the event that there are extraneous parts in my outbuilding] a separate 10mm bonding cable back to the MET in the house [as is recommended] then have i not also extended/exported the EZ too so everything will be ok?

What i cannot understand is, what is the difference between me building a 10 foot long outbuilding 20 feet from my house and doing this with the supply [which lots of people seem to think is wrong], to making a 30 foot long extension instead of the outbuilding and wiring it in exactly the same way?

What i am trying to say is, if i built an outbuilding and wired it in 2.5 and bonded any extraneous parts that there might be, [say i built it round an existing gas pipe in a long demolished shed or something] with the required size cable [presumably 10mm] back to the MET] what would be wrong with that?

Say the DNO came along and said "we are not having that" what would happen if while they were gone, i built like a hallway, and extended my extension back to the house to make it all one piece? There would be absolutely nothing they could say then, but what would have changed electrically??

Can i just add, PLEASE PLEASE can you all take on board here that I am not picking holes in anyones idea's here, or trying to say that i know better than anyone else either, I am just trying to learn from all your collective experiences, as to why things are done the way they are.

Thanks all

john

 

[Zeespark]

John, what you have to take into account when exporting an EZ with TNCS, is that because the Neutral and Earth are one, that a fault on that system will likely cause problems for households further along the electricity supply chain. You dont have this issue with TNS/TT precisely because a sheath or rod/mat/plate etc is handling the earthing by themselves, not with a neutral in the equation like TNCS.

Andy

 

[mikep]

To make it clear the setup is as follows:

House with Consumer unit with RCBO Feeding 2.5mm SWA to garage CU with BS60898 MCB's armour and 1 x 2.5mm core plus 1 x 10mm bond to both MET's

Main bonding in 10mm to both gas pipes entering the house from house MET, The garage is 1 metre away and has gas supply in steel pipe and 1 outgoing steel pipe set in ground going into house, it also has another high level ( 2.2metre high ) 28mm copper pipe going from meter to house both bonded on both CU MET's so pretty well connected to each other, so no segregation can be achieved. that is as clear as I can make it for anyone being confused.

 

[steptoe]

Sounds OK, 1 thing we need to be clear on here for other posters,

You are not exporting PME, you are extending the EZ, there is a massive difference.

 

[apprentice87]

Hi, Yes, i would agree with steptoe, sounds good to me too!!

john.

---------- Post Auto-Merged at 18:55 ---------- Previous post was made at 18:49 ----------

Forgot to say, Yes, i think what people get all upset about [with good reason!] is exporting pme outside of the EZ. As, like steptoe says, you have properly extended the EZ, i think we can all agree all is well. [Hopefully]

Thanks all,

john.

 

[mikep]

I have come to the conclusion that it only an extension of the EZ, with all the pipe-work and bonding in place I am happy that the amount of bonding in place should be sufficient for any fault, I also contacted NAPIT Tech who said Just make sure it has a 10 mm bond to both CU MET's, all sounds good to me therefore I think we can put this one to bed.

It has been very interesting on all the views which is what the forum is all about.

Please feel free to comment on this.

Till the next time regards all, Mike.

 

[steptoe]

I have come to the conclusion that it only an extension of the EZ, with all the pipe-work and bonding in place I am happy that the amount of bonding in place should be sufficient for any fault, I also contacted NAPIT Tech who said Just make sure it has a 10 mm bond to both CU MET's, all sounds good to me therefore I think we can put this one to bed.It has been very interesting on all the views which is what the forum is all about.

Please feel free to comment on this.

Till the next time regards all, Mike.

if NAPIT actually said that then they need a good slap,

you only have 1 MET,

like you only have one EARTHING CONDUCTOR,

 

[apprentice87]

Yep, Steptoe is right there, You only have one MET. That is at the origin of the supply, and likewise only one earthing conductor. So far as i know the "second" one, ["MET" that is] in the second "installation" would actually be classed as a BEMT.

john

 

[mikep]

Sorry Steptoe, my words used not theirs I am the one wanting the slap as I wrote it and fully understand what you mean and know that you have to be pedantic as it has to be worded right so I will be in Thursday afternoon for my punishment and looking forward to it !!

Regards, Mike

 

[Larnacaman]

For a bonding conductor you use the copper equivalence, now steel is around 8 to 1, so PME 10mm copper would require a copper equivalent of 80mm steel, neither 6mm or 10mm csa armor meets this requirement.

Yes ....your right, i had that niggling feeling i was missing something, and it was the copper equivalence requirement for bonding!!!

How i let pass over my head i haven't a clue... lol!!! Apologies for not getting back to you sooner

 

[ian932]

John, the DNO, under the ESQC Regulations have precedence over the IET/ESC, by LAW. If you phone your local DNO up and ask if you can extend a TNCS supply outside of an EZ, they may tell you that you CANNOT do this. What the IET/ESC say in this matter in the example I have just given does not stand up to legal and official scrutiny.Andy

Totaly agree and I've asked them no end of times, sometimes they say no, rarely they say yes but when asked to confirm in writing its always no can do. So I never ask now and always TT remote buildings - CYA