CU & Bonding again!!!

[Ponty Massive]

Sorry about this as I know it's been done to death.

I've decided after moving into our house about a year ago to replace the consumer unit. It's an old 3036 with 4 cuircuits.

Opened it up today for the first time to find 3 ccts to the lighting fuse, 5x 2.5 reds in the one 30A fuse, 1 to the heating and one not used. I'll be going through that lot possibly tuesday!!!

Anyway, the supply is PME with 60A fuse, 16mm tails and 6mm earth to CU. Bonding to gas and water in 6mm also.

I'm going to be putting in RCBO's to each circuit but to upgrade the bonding to 10mm is going to be a nightmare as there has been an extension added to the house at some time and running in new 10mm will mean pulling the house apart!!

Ze is good and existing bonding shows no signs of thermal damage .

So my question!!! Do I need to contact the DNO to upgrade the main earth (remembering Ze is fine) and if not, would it be exceptable to use the existing 6mm bonding?

Cheers all.

 

[rocker]

If it's a TN-C-S system the cable from the CU to the earth terminal is your responsibility, at least that's what I think I may be wrong.

 

[Sparky Ninja]

Correct, if it's a PME then 10mm will be required so as to achieve lower touch voltages and to accommodate the expected high perspective fault currents.

 

[telectrix]

agree with you on that rocker. think it might be permissible to leave the existing 6mm bonding to gas and/or water, as it was compliant when installed. bit of a grey area if replacing would cause major problems. could it be alternative to run new 10mm externally in pvc tube?

 

[Guest123]

Taken from ESC 17th Ed Q&A section......


EDQ12

When carrying out electrical work on an installation forming part of a TN-C-S system, is it necessary to upgrade existing 6 mm² protective equipotential bonding to 10 mm²?​

EDA12

Not necessarily. If the existing 6 mm² bonding connects all the extraneous-conductive-parts to the main earthing terminal, has been in place for a significant time and shows no signs of thermal damage, then it may not require to be upgraded.​

131.8
544.1.1 ​

 

[Ponty Massive]

Thanks guys, Can't run the 10mm externally because of the extension to the house. The meter cabinet (which was originally external) due to the extension is now in our spare room and looks an eye saw. Think originally the ground floor of the extension was designed to be a garage then had been changed to another room hense the meter cabinet is now inside. In an ideal world I'd like to get the meter and main fuse relocated along side the CU but dread to think how much this would cost (probibly not that much work as it's just the other side of the wall).

Main earth comes from the cut out direct to the CU with gas and water also connected direct to the CU so no MET. Don't think I can renew the earth to the cut out legally?

Gas and water are at the other side of the house and would be a case of ripping out floors (laminate) and chasing walls!!

 

[Ponty Massive]

Thanks Lenny, yes I had read about that clause (hense why I mensioned shows no sign of thermal damage) but doesn't that go against the grain? If this is the case, why go through all the hastle, cost and potential loss of a job if we can just leave the 6mm in?

Don't get me wrong, if it's within regs then it will help me out no end!

 

[Sparky Ninja]

131.8 & 544.1.1

There's nothing there that I can see that supports the ESC's opinion.
Do you think that changing a CU might be considered as 'not require to be upgraded'?

 

[Guest123]

131.8 & 544.1.1

There's nothing there that I can see that supports the ESC's opinion.

I know, thats why I threw it in.

I had a barney on here about this very subject ages ago.....I'll see if I can dig it up.

 

[Sparky Ninja]

If it's impossible to do, then put it down as a limitation or deviation, simples.

 

[Sparky Ninja]

I know, thats why I threw it in.

I had a barney on here about this very subject ages ago.....I'll see if I can dig it up.

Gotcha.

 

[Ponty Massive]

Thanks all, what about the 6mm from the cut out direct to the CU?

 

[Guest123]

MEC should be upgraded IMO, the MET obviously isn't visible on the side of the cut-out then??? Is it under the small plastic cover to the right of the fuse???

 

[rocker]

Yea it may be under a plastic cover but probably not crimped..... I see you're in S Wales, I know that Western Power do not class any earth joint other than a sweated joint as 'their responsibility' so with a TNCS you should be able to access it without cutting any seals.

 

[Ponty Massive]

This is it at the moment

 

[Guest123]

mmmm, that seal looks a tad brittle from here......a freak gust of wind and it looks like it may come off!!!

 

[Sparky Ninja]

mmmm, that seal looks a tad brittle from here......a freak gust of wind and it looks like it may come off!!!

It's funny, in all my years I've never actually encountered one of these so called 'seals' before

 

[Ponty Massive]

I hear what your saying Lenny . Just want to make sure it's all kosher as I'll probibly use it for my assesment. Another reason why my 6mm bonds are concerning me!

 

[Ponty Massive]

I may give western power a call and see what the damage is to move the lot next to the CU.

Has anyone come across the "using 6mm bonds" during their assesment?

 

[Guest123]

It's funny, in all my years I've never actually encountered one of these so called 'seals' before

Me neither......I had to google "the funny piece of wire on top of a fuse" before I knew what it was called!!

 

[rocker]

Mate if you're using it for your assessment I'd be upgrading to the full all singing, all dancing bells and whistles.

 

[oldtimer]

I asked this question on the voltimums website:-
On a TNS installation in a flat the DB has to be upgraded to a 17th edition unit because the existing unit is damaged but the customer does not want the earthing to the gas and water upgraded from 6mm to 10mm.
Where does the installer stand with regards to this situation
With regard to your question, you may well want to refer to the Electrical Safety Council's Best Practice Guide 6 on replacing a consumer unit. See their website www.esc.org.uk
Generally speaking you must leave the installation in no worse a condition. Where the earth bonding does not comply with current requirements then the competent person should be able to use his knowledge and experience to determine if it is safe for the bonding to continue in service. For a TN-S system the 6mm2 bond may well suffice. If it is a TN-C-S the distributor may require the bond to be 10 mm2

This was answered by Select

 

[Ponty Massive]

Thanks rocker I know you're right, it's just gonna be a blo%dy nightmare. I keep thinking about that ECS comment about the 6mm as aposed to destroying my house to get the 10mm's in.

Thanks again!

 

[Ponty Massive]

Thanks oldtimer, Ze is fine (with 6mm from PME cutout), continuity to gas and water fine also. DNO has supplied a 6mm therefore I would assume 6mm bonding would be adequate. If I was doing this job for someone else, seeing the work that is involved, I would stick with the 6mm and write it on the EIC as a deviasion, however to use it as an assement is another story!

 

[rocker]

Maybe you're looking at it the wrong way.... if you were to upgrade, would you have to run the bonding the way it's already been run, or would it be doable under floorboards etc?

 

[malcolmsanford]

Reg 544.1.1 I think a lot of people just see the part about 6mm^. The second paragraph clearly states that where PME conditions apply, except for highway power supplies, then the bonding condutor shall be selected in accordance with the neutral condutor of the supply and Table 54.8

That clearly states that 35mm^ or less you need a 10mm^ conductor.

The first paragraph deals with all other systems TN-S, TT, IT which states that bonding condutors can be half the size of the main earthing conductor of the supply, but a minimum of 6mm^. In other words if you had a 10mm^ for any reason, you could not use a 5mm^ if there was such a beast, you would use the minimum of 6mm^

It's a strange reg in many instances as I think it still identifies main supplies of 16mm^ and so the Bonding could be a 8mm^ if that existed. Instead of just saying a blanket 10mm^ in the minimum, it says 6mm^ is for those 16mm^ supplies

 

[Sparky Ninja]

I asked this question on the voltimums website:-
On a TNS installation in a flat the DB has to be upgraded to a 17th edition unit because the existing unit is damaged but the customer does not want the earthing to the gas and water upgraded from 6mm to 10mm.
Where does the installer stand with regards to this situation
With regard to your question, you may well want to refer to the Electrical Safety Council's Best Practice Guide 6 on replacing a consumer unit. See their website www.esc.org.uk
Generally speaking you must leave the installation in no worse a condition. Where the earth bonding does not comply with current requirements then the competent person should be able to use his knowledge and experience to determine if it is safe for the bonding to continue in service. For a TN-S system the 6mm2 bond may well suffice. If it is a TN-C-S the distributor may require the bond to be 10 mm2

This was answered by Select

Nobody just says yes or no anymore

 

[Ponty Massive]

I see. So it is a minimum of 10mm then and there's no way around it!!! As widdler say's, no matter who you ask (people who make the rules) no one will give you a stright answer.

If it was the case that there is no way these bonds could be changed, it would be crazy to stop someone having a safer and upto date board with RCD's and MCB's just because the bonding cannot be changed.

 

[malcolmsanford]

As you konw the regs are not law, and if you want to leave it 6mm^ then that's your call as the designer. The trouble with that is

a) As it's your assement the assesor will pull you on it as it's not to the Regs

b) god forbid if anything happened and your in a court of law you have to argue why you decided that 6mm^ was satisfactory, so it's not worth it do as the Regs say and your covered.

The problem is and you know, there is really no such thing as no way to do something, there is always a way, just maybe be difficult or cause problems, unfortunately the regs don't take into account that the customer or you don't want a 10mm^ cable clipped surface all over the place.

 

[oldtimer]

I see. So it is a minimum of 10mm then and there's no way around it!!! As widdler say's, no matter who you ask (people who make the rules) no one will give you a stright answer.

If it was the case that there is no way these bonds could be changed, it would be crazy to stop someone having a safer and upto date board with RCD's and MCB's just because the bonding cannot be changed.

I totally agree I submitted this question along with "can I use conduit as an earth if upgrading a fuseboard" as I live in Edinburgh and I am starting to get enquiries from potential customers who want a "safety board" but do not want to rip up their house ie laminated floors
etc when they have 6mm cables to the gas and water yes I know the regs says 10mm but I am hearing from people in the trade and know who say if TNS and the 6mm is in good nick ok but if TNCS then you must upgrade to 10mm. Thing is I have already lost 2 jobs because " I only wanted a new board" reply

 

[Ponty Massive]

The problem is and you know, there is really no such thing as no way to do something, there is always a way, just maybe be difficult or cause problems, unfortunately the regs don't take into account that the customer or you don't want a 10mm^ cable clipped surface all over the place.

Your right, there is always a way, just costs more to put the house right when your complete, than the original job.

Thank you everyone for your help and advise. This forum is a wealth of knowledge. I've learn more from this site than a 4 year apprenticeship!!

 

[nickblake]

Belive it or not the tails that go from the Meter / and main earth to the CDU are not the DNO,s responcabilty its the customers , but us sparks are not allowed to cut the seals what a joke