RCD for burried sub main to garage???

[ADS]

OMG - The mind boggles!!

this visit is the one at the end of my first year

I did sit my 2391-20 design & verification last yr so hopefully that'll help.

Then.....

sorry, don't understand DNO, what's that an abreviation of?

i've read that sub-main disconnection times are 5sec

can you point me in the direction of the 600mm reg.

the supply in the house is TNC-S/PME.

If it is classed as extraneous, can't i bond it at the fuseboard in the garage.

is concrete conductive??

Seriously, How did you get through your first assessment? - and how the hell did you pass the 2391-20?????

 

[steptoe]

2391-20 isnt a proper exam AFAIAA.

 

[ADS]

2391-20 isnt a proper exam AFAIAA.

I'm not sure if you're taking the p**s here, Steps.

It's a design qualification - mainly a project that you have to submit - and you have to pass the exact same practical as you do for the 2391-10.

From what I've read it's pretty difficult - I haven't done it though.

The reason I mentioned this, with regards the OP, was due to the fact that the 'design skills' seem to be lacking with his 20A plug-in MCB / 4.00mm T&E / 6.0mm 5-core SWA - and buried at 150mm lol

 

[apprentice87]

Hi, Measure the resistance between the metal parts in the shed and your MET. If it is more than about 25,000 to 50,000 ohms [depending on circumstances] then the metal bits are not considered "extraneous" anyway and do not require bonding. [or at least that is my understanding of things!!!]

I had a site visit from the DNO to something i am doing at the moment [a new PME supply to a 110 metre submain] and they did not even mention "exporting" anything. Unless it is something that is PROHIBITED by BS7671 or the ESQCR "The distributor shall not connect his combined neutral and protective conductor to any metalwork in a caravan or boat" I do not think the DNO are even interested...

Having said that, what Steptoe says "The problem with the earth is it belongs to the DNO, they will not usually permit you to use it outside the normal EZ" is exactly right, outside being the operative word.

If you extend the EZ properly, then all should be well [bearing in mind PME is a stupid system anyway] but if you extend it [the earth] outside the EZ then you are looking for trouble!!

john..

---------- Post Auto-Merged at 01:18 ---------- Previous post was made at 01:13 ----------

Just read the bit about the lights are mounted on the steel work! Think i might be bonding the steel work after all! [or at least connecting the lighting cpc to it!]

 

[Sidewinder]

2391-20 isnt a proper exam AFAIAA.

Steps,

I think you have mixed up some numbers here, I do believe that the 2391-20 is a proper exam, it is the follow on from the 2391-10.

It is the "NEW" number for the same course, which used to be called 2400.

I found the 2391-20 Design & Verification, more difficult and a lot more work than the 2391-10 Testing & Inspection.

It covers a much wider field than the other exams, as it covers design in much greater depth and things like phase load balancing, diversity, voltage drop calculations, ring main load balancing and a multitude of other areas that are not covered in other courses.

You have to undertake the same practical exam as the 2391-10 unless you already hold this, in which case a copy of your certificate is required, you have a full 3 hour closed book exam which covers regs, design calculations, design considerations, inspection & testing, as well as general electrical theory.

On top of this you have a project to complete, this will be often a complete design of a commercial building where by you have to specify everything down to the switches on the wall, all cable sizes, any sub mains boards, lights and provide cable calculations for every circuit in full, as well in mine anyway, we had to install certain ring circuits as it was in the brief, and these had both fixed and variable loads, where by we had to prove by calculation that it would not be expected to overload the ring in anticipated use.

We also had to provide manufacturers literature for all of the equipment we specified, and this by the way included the containment and wiring support structures through all aspects of the project.

There were certain wiring systems specified, to for example ensure that you used SWA somewhere IIRC the goods lift in mine had to have an SWA supply.

IIRC the guide hours for the project are 40.

My final project document, including, circuit layout drawings (A3), and only the relevant sections of the manufacturers literature being included, that is only the sections for the kit I was actually specifying, submitted was 323 pages of A4 apart from the drawings.

Apart from my degree courses, I think it has been the hardest course and a lot of work.

Ask the Rev James also as he has done this course.

IMHO I think you are mixing this up with the 2392 course, for initial verification the course that is touted as an introduction to inspection & testing.

However I can't comment on the 2392 course as I have not taken it, I did the 2391-10 & 2391-20

Try here:

Certificate in Inspection, Testing and Verification of Electrical Installations | Construction and Building | Electrical installation | City & Guilds

& here:

Certificate in Fundamental Inspection, Testing and Initial Verification | Construction and Building | Electrical Installation | City & Guilds

HTH

 

[james KEI]

Have just spoken to my NIC asessor. He has told me that if you have a TNS supply then this situation would be fine. If you have any extraneous, bond it at the local DB.

If you have PME the situation is fine if there is no extraneous conductive parts

If there are extraneous, TT the garage end, as has been done in the Picture part of this forum, labelling the earth as fictional & do nit connect.

His opinion is that my 'A' frame roof does not create another potential as there are no metal reed bars from the roof that are burried in the ground, it is just sitting on top.

The reason I knew nothing about this is because there is next to nothing in our regs regarding this and I have not come across it before. I had looked at 7671 and not come up with a lot. It is all very well you lot saying you can't do this & you can't do that but you haven't shown any evidence of where it states about this exporting the earth business & I don't know where to find it as yet.

No, I don't know wether concrete is conductive, I always thought we earthed it because of all the steel structure/reed in a lot of it that is in it. I've googled it and this is what has come up, two different types of concrete

Electrically Conductive Concrete: Properties and Potential

Answers.com - Is concrete conductive

I don't confess to know everything & I was always taught that you don't need to but, should you need to know anything, you can look it up and find it. You know what they say about the people who do... All the gear and no idea...

2391-20 is a 'proper' exam thanks. It replaced the old 2400 and prior to that the part C which, according to the JIB grants you Technician status. Yes it was a bit difficult especally as I did my 2391 in 2004, quite a gap, but was enjoyable and a good refresher. It's supprising how much you know, you've just got to dig back a but to find it.

I'm also going to ask my friend Sam on the exporting earth jaz. He's in his 3rd year of a degree to become a chartered Electrical Engineer. He also works for EDF networks (thinks it's just been bought out) and designs LUL substations.

The radiator (no I don't have one in the garage) was an example of the EZ. So the rad' is connected to the supply earth but the window isn't, they're within touching distance of each other and that is sitting on brick, upon concrete blah blah and then ground. The window isn't bonded, is that a different potential??!!

So, garden lighting, is that exporting the earth then. It's outside, outside of the EZ too??

I don't see the problem with the way my garage is done. What's wrong with it being on a 20A, it offers discrimination and to meet the disconnection time of 5sec required, ok it's a 3871, the regs still recognise these mcb's and eventually the board will be swapped, but it works and is safe. Ok, 6mm 5core is OTT but it was a leftover I had and

didn't cost anything. If I'd done it buying everything I would have done the whole run in the swa to save having a joint. The 20A also helps keep the Ib & In down so not to bump the cable calc up too much with all factors in and is plenty for what I'll be doing in the garage.

How did I pass my initial inspection and how did I pass my 2391-20, I don't appreciate those comments and your not here to judge wether I'm competent or not. I only signed up for a bit if advice and guidance here and there are, I assure you, there are a lot worse electricians out there than me and I am not a bodger.

Many thanks to those who have genuanly help,

Cheers

James

i forgot.... i asked where the reg was for the 600mm depth as i couldnt find this particular figure and wondered if i had missed something so wanted to clarify it and as it turns out, as the chap said, that was pulled from the ammendment that's not yet published.

i had looked up, with regard to my original question, and had come to the conclusion it didn't need to be RCD protected BUT just incase i had missed something i put the post up on here, as much as anything to see different people opinion as 7671 is open to interpretation and you could well understand it differently than i.

 

[NozSpark]

James,

I'm glad you got a definitive answer from your assessor and that you posted back your findings,,, that's one way that we all learn!

There's only one more question that I've got... What did you do with the unused cores of the SWA?

 

[james KEI]

the left over cores, i think, at the joint end were terminated into spare din connectors and at the DB were connector blocked. i don't remember doing anything to identify them, they were already number stamped (all cores were plain white insulation)

thanks for the help. it's not that i was trying to swerve finding out myself but clarify i hadn't missed anything and then this whole can of worms (exporting the earth) popped up that i had never heard about.

thanks,

james

 

[NozSpark]

There was a publication not too long ago that had an article on unused cores in multicore cables...it advised that they should be terminated at both ends and earthed at at least one end....obviously also identified!

I'm afraid I can't remember the publication though, it would have been either the connections, switched on or professional electrician magazines

 

[ADS]

Nice one, James

I like someone who can argue back without resorting to insults. :Applaud

You handled the criticism well and gave a decent account of yourself.

I know it's not your first thread, but welcome to the forum.

People do go easier on you once they know a bit more about you (except Steptoe, he gives everyone a hard time, especially if you mention a shed) - hopefully you haven't been put off.

 

[binky]

Exporting earths, and a long argument - be warned James, it happens every time ROTFWL

 

[apprentice87]

Hi James, First off, I am sorry if anyone has upset or offended you. Thing is, you will find that many of the posters on here are VERY VERY experienced, and although set in their ways is not the right words, they hold strong opinions about something they have been doing for a great many years and i suppose sometimes it can come across as a bit stroppy, but honestly, nobody intends to be like that i can assure you.

Now, as to this "exporting" PME lark!! Nothing but nothing promotes more arguments than this!!

Here though, is a link to an article published by the IEE, so i think that they might just know what they are talking about!!

electrical.theiet.org/wiring-matters/16/elect-inst-outdoors.cfm?type=pdf

I think you will find this answers a lot of your questions!!

Still, there remain a lot of theoretical arguments both for and against doing this sort of thing, and all of these arguments have their supporters, both for and against, and for very sound theoretical reasons too!!! They will never agree though, because you see, both camps have very sound reasons for holding the opinions that they do.

As to the correct depth to bury cables, part 7 of BS7671 covers all the requirements that you should [unless you want to end up in a coroners court one day] observe for this in "special locations" such as caravan parks and farms and all that sort of thing.

Outside of these areas it is down to the rule 522.8.10 which amongst other things states that they have to be deep enough to avoid "reasonably foreseeable disturbance" So, just how deep that is, is a matter for you to decide using your skill and judgement!!

john..

 

[steptoe]

James, I have not, nor do I, set out to offend or derate anyone, Sorry if I have come across that way.

As has been said, I have strong opinions as to NOT exporting TNCS earth under most circumstances.

IMO, if you understand the implications on exporting it, and the conditions required to export it, then you wouldn't most likely need to ask,

 

[Voltimax]

James,,FYI Admin put a very helpful little plug in on this site.. if you hover your mouse over any acronyms that have a dotted line under them it shows you what they stand for

KUGB, KGB, EKGB, TSUK, TSKR, SKIFF.......... Nope, sorry it ain't working

 

[NozSpark]

Eh? :coffee

 

[Voltimax]

A little exercise for admin, he can go find out what they stand for and use his magic plug in, lol

 

[ian932]

A little exercise for admin, he can go find out what they stand for and use his magic plug in, lol

I suspect Admin has more than enough on his plate without playing hunt the acronyms.

Personally I hate the bloody things they are making us lazy in speech and writing.

If someone say

 

[kme]

I tend to agree - but I`ve become lazier since starting to come here regularly......all the iirc, afaik, and the like, I had never seen before I came here!

And as for those people who scatter "lol" all over their posts - Grrrrrrr

 

[binky]

is asap ok then????

 

[ian932]

is asap ok then????

yes that is better