Main protective bonding

[Tony Dent]

Just installed a new consumer the tails are 25mm with 10mm main protective bonding. Regs table 54.8 states tails up to 35mm require 10mm bonding 35+ requires 16mm so what is it to be 10mm or 16mm I would leave this in but want to make sure as this is my first stroma self certification assessment and need to be correct.

Tony

 

[steptoe]

10mm MEB

16mm Earthing Conductor

for 25mm tails

on a TN system 

 

[Tony Dent]

This is tnc-s system domestic at training centre our test rigs are set up with 16mm but out in the field I'm coming across tails of 25mm as to the regs table 54.8 minimum cross-sectional area of main bonding conductor in relation to the neutral of supply 17th edition amendment 3 says 35mm or less 10mm over 35mm 16mm.

Tony

 

[binky]

there are various sizing clauses, but you will find somewhere that it also states 'half the size of the neutral', so for 25mm that would be 12.5mm which doesn't exist, so we up it to next size bigger which is 16mm

 

[Sidewinder]

Steps is correct.

Bonding 10mm2

Table 54.8

Earthing conductor 16mm2

Table 54.7

For tails 25mm2

If you're worried, just do the adiabatic on it and check the suitability that way, you'll probably find that it comes out much less, and, the sizing requirement is due to the potential diverted current flows.

However, note that not all TN-C-S is PME, however, all PME is TN-C-S, at the origin when fed from the public supply.

There are ways of creating localised PME on TN-S & TT systems, which are not TN-C-S but that gets complicated.

Some TN-C-S is PNB, so therefore not PME.

 

[Andy™]

oh look, another 'training centre' has has missed teaching the basics like what size of earth should be used. wonder what else they havent taught him?

 

[Sidewinder]

oh look, another 'training centre' has has missed teaching the basics like what size of earth should be used. wonder what else they havent taught him?

The thing is AndyTM it's not his fault!

The issue is just like the pre-Brexit vote rubbish that was spewed by the politicians, the training centres are full of rubbish promotional nonsense too.

 

[Andy™]

The thing is AndyTM it's not his fault!

thats debatable. not really his fault that the course is inadequate, but if those doing the courses done their own research first before paying thousands....

if people didnt do the inadequate / fraudulent courses then they simply wouldnt exist

 

[Tony Dent]

Many thanks for the help please can I explain that I have been taking this cause through T4TS I understand its not every electricans greatest way of undertaking any training but let's be honest here I'm 47 years old I work full time and to go to my local college to do the cause they want 2 nights a week for 3 years with work this was not an option could not be done also for a 47 year old with kids, house, cars etc an apprenticeship being paid £150 a week would be an impossibly. Doing the cause this way and through T4TS has been the only option for me yes I will say it's a rip off and not a good company to go through but my training centre is ERR in Leeds who I can not fault are very good and help and support all the way these trainers are professionals who have had many years in the industry they have nouthing to do with T4TS.

If it's as bad as people say then surely city and guilds would not want to approve the training centres, I have city and guilds certificates as I would have got if I had done the same at college.

I can't in any way fault ERR but would not recommend T4TS.

 

[Andy™]

there is no possible way you can learn enough in the time you have on those courses, as you have already proven. on the plus side, at least you are trying to understand it more than some do and looking through the regs for yourself. and if you do pass your assessment, then it just goes to show how much of a scam all these schemes are. no disrespect to you, but there is no way someone doing a short course should be able to be passed by them as competent to carry out work on your own

they were originally designed for older electricians who knew what they were doing but didnt have any formal qualifications to prove it. then they made them for anyone so the bosses could make more money by claiming if you do the course you will be fully qualified within weeks and earning 50K +

the best way would have been through college

 

[Tony Dent]

I started this cause in 2012 it's now 2017 this will be my 5th year what is it at regional college 3 years? Also it dose say the cause can be done between 12 to 36 months if you can do it in 12 months then your clever. I have the chance to retake any of the weeks taken at ERR if I'm not happy and want to go through any thing again ok the first time I failed the c&g fundamentals of inspection testing and initial verification as this happened I was invited back to ERR for 3 days one on one with an assessor to help me and it did as I got high pass mark so they have helped and offer the help if needed to it's not rushed not in my opinion. May I ask what certificates you have I take it you have done c&g exams if so what is the difference between yours and mine it can't be a load of rubbish if I hold the same certification as you, you must have gone through the same as I have to have taken the same exams.

Seriously don't be unfair I'm happy for you if you slogged your guts out in  your apprenticeship but really apprenticeship is gaining experience isn't it that's what apprenticeships are for experience in the field while at college and if you have just done 3 years at college doing your cause then it's taken me longer so so how can't it be rushed?

 

[Sidewinder]

Tony, your last message sums it up, you get the qualifications, but not the experience and competence.

Remember, competence is defined by HSE.

It includes qualifications, training, and experience.

You get the qualifications at college, or the training centre, but, you don't get the experience to make you competent at the end of the course.

Not your fault, as has been said, the courses have been *******ised for profit.

 

[Phoenix]

Some TN-C-S is PNB, so therefore not PME.

Cat amongst pidgeons....

Is a PNB setup TN-C-S at all? Is it not TN-S? Afterall N & E are separate after the point at which the LV electrode is attached.... does the fact that that this happens the other side of the wall in the customers switch board, rather than in in the transformer room with a DNO open fuseboard change much....

It certainly doesn't have the disavantages generally found with TNCS supplies and if TNCS is disallowed because of these, then considering the PNB set up being TNCS might cuase problems

 

[Sidewinder]

Not always, you can have the HV & LV electrodes connected appropriately at the TX, with the N as the CNE to the consumers switchgear, and the split there so it is TN-C-S as it is separated at the consumers switchgear/presentation, the same as a domestic TN-C-S, but without being PME.

So, again, not clear cut.

 

[steptoe]

Not having a go at the OP directly,

But you will find that the C&G 2391 was watered down into the 2394/5(iirc) in order to increase the pass % , 

So I'd say that a 2391 trumps a 2394/5 any day of the week.

Only my opinion tho, and the OP did ask if his qualifications were of equal standing.

 

[Phoenix]

Would that be PNB though? I don't think it would, I Agree though that it would be TNCS but not PME.

(I think I've only seen that once though)

So we have:

1) TN-C-S thats PME

2) TN-C-S that isn't PME

3) PNB (as a form of TNS)

 

[Sidewinder]

I believe it would be PNB (& I'm not the only one), as there is one PNB at the consumers switchgear, common with a dedicated on site HV Tx.

 

[Phoenix]

Its too late to visulise properly.....I'll think about that one some ore on the drive to work tommorow ater a sleep!

Most times with a dedicated HV trasformer it seems to either be (normal) PNB with the earth electrode at the cutomers end, or in a lot of cases these days, standard TNS wiith a spearate earth all the way back to the transformer enclosure.

The one I remember had the customers 400A panel board in the same room as the transformer and HV switchgear (one of those odd arrangements from years ago) The DNO had seen fit to replace the customers padlock with their own and left the customer not able to access their switchgear... a dual access arrangement had to be requested and a lock with a bar that had a diferent padlock each end was fitted.

Anyway, I digress, A cable head and CT cab were next to the panelboard. A few metres of 3C waveform came out of the transaformer terminal box and looped around and into the bottom of the head