Size of tails, SWA and earth size.

[Amp David]

I posted the other day regarding advice on a switceh fuse for when the CU is a distance from the meter.

I've decided on using a 60amp switch fuse which will be fed with 25mm tails. From the switched fuse to the CU, roughly 9-10 meters, I have specced 10mm 2 core SWA and a 16mm earth. The supply is TN-C-S, so have specced the earth to match that of the tails at the meter, rather than the size of the SWA.

Is this the way in which the regs describe sizing if the main earth. or should the earth be sized on the SWA and not the supply tails.

Maybe quite simple to some, but would like other opinions on it

Thanks

 

[pennywise]

How much more would it have been just to make the SWA a three core 16mm? woops sorry seen your other thread didn't realise the bonding will go back to the main head MET. 10mm three core SWA for me then 16mm from switch fuse to MET but as telectrix says future proofing 16mm 3 core could still be an option

 

[kmcgold]

i would use 16mm to met and then 10mm

 

[telectrix]

How much more would it have been just to make the SWA a three core 16mm?

just what i was thinking. better overkill than have to replace in future.

 

[Amp David]

How much more would it have been just to make the SWA a three core 16mm? woops sorry seen your other thread didn't realise the bonding will go back to the main head MET. 10mm three core SWA for me then 16mm from switch fuse to MET but as telectrix says future proofing 16mm 3 core could still be an option

Gas bond will be run to the head MET, but water will be connected via earth bar in the CU.

One of those jobs i htink where customer is old, wants to spend as little as poss so couldn'r care less about anyone who comes in after them.

Thanks for the input

 

[pennywise]

Gas bond will be run to the head MET, but water will be connected via earth bar in the CU.

One of those jobs i htink where customer is old, wants to spend as little as poss so couldn'r care less about anyone who comes in after them.

Thanks for the input

I can picture the customer right now 16mm 3 core SWA for me then, when I was after a load of SWA one of the guys put this link up really competitive prices if I remember

https://www.electriccableco.com/electric-cable-shop.htm

 

[malcolmsanford]

Gas bond will be run to the head MET, but water will be connected via earth bar in the CU.

One of those jobs i htink where customer is old, wants to spend as little as poss so couldn'r care less about anyone who comes in after them.

Thanks for the input

Technically you shouldn't do that mate. As there can only be one MET and bonds have to go back to that. What you saying is you will have 2 one at the head and the other as the earth bar of the CU.

Plus also mate would not advise using where the DNO link as YOUR MET as that is theirs. I know you see it quite a lot but usually the DNO can get a little upset with that.

If it were me mate, I would fit a MET at the header, bring the earth conductor from the TNC-S into that. Then run your bonds back to it, and the CPC for the CU. Or the other way round the MET at your CU and run the bonds back to there.

 

[pennywise]

Technically you shouldn't do that mate. As there can only be one MET and bonds have to go back to that. What you saying is you will have 2 one at the head and the other as the earth bar of the CU.

Plus also mate would not advise using where the DNO link as YOUR MET as that is theirs. I know you see it quite a lot but usually the DNO can get a little upset with that.

If it were me mate, I would fit a MET at the header, bring the earth conductor from the TNC-S into that. Then run your bonds back to it, and the CPC for the CU. Or the other way round the MET at your CU and run the bonds back to there.

It may be slightly easier to run a new length of 10mm from the gas to the new CU position and make that end the main MET. I'm only guessing that the water is in the house and may be a pain to rewire back to the head in the garage, as opposed to the gas which will only have to be clipped along the garage then pop through into the CU. Sorry might be well out with my assumption

 

[malcolmsanford]

It may be slightly easier to run a new length of 10mm from the gas to the new CU position and make that end the main MET. I'm only guessing that the water is in the house and may be a pain to rewire back to the head in the garage, as opposed to the gas which will only have to be clipped along the garage then pop through into the CU. Sorry might be well out with my assumption

You may be spot on Pennywise but technically you can't have the bonds at 2 different MET.

 

[Amp David]

Technically you shouldn't do that mate. As there can only be one MET and bonds have to go back to that. What you saying is you will have 2 one at the head and the other as the earth bar of the CU.

Plus also mate would not advise using where the DNO link as YOUR MET as that is theirs. I know you see it quite a lot but usually the DNO can get a little upset with that.

If it were me mate, I would fit a MET at the header, bring the earth conductor from the TNC-S into that. Then run your bonds back to it, and the CPC for the CU. Or the other way round the MET at your CU and run the bonds back to there.

Cheers Malcolm.

On every TN-C-S, I put a 4 way earth terminal near to the head and link the DNOs terminal to this. Never hook it all to the DNO terminal, never room anyway.

It may be slightly easier to run a new length of 10mm from the gas to the new CU position and make that end the main MET. I'm only guessing that the water is in the house and may be a pain to rewire back to the head in the garage, as opposed to the gas which will only have to be clipped along the garage then pop through into the CU. Sorry might be well out with my assumption

Gas meter is in the garage on opposite wall to the supply head. Water is in the house as you enter the kitchen. Will have to bring the water bond past the CU on the way back to the MET at the supply head then

 

[pennywise]

You may be spot on Pennywise but technically you can't have the bonds at 2 different MET.

Sorry mate I totally agree with what you say, all I was saying was it maybe easier to take both gas and water bonds to the new CU position rather than having to reroute the water bond back to the head. cheers

 

[tonys]

You may be spot on Pennywise but technically you can't have the bonds at 2 different MET.

So lets say he carries a 16mm from the incomer to the cu and runs a 10mm for the gas to the cu and a 10mm for the water back to the incomer and labels then both. Its all part of the same installation, what is wrong with that? not a dig but a genuine question? where does it fall foul of the regs?

 

[malcolmsanford]

So lets say he carries a 16mm from the incomer to the cu and runs a 10mm for the gas to the cu and a 10mm for the water back to the incomer and labels then both. Its all part of the same installation, what is wrong with that? not a dig but a genuine question? where does it fall foul of the regs?

Somewhere in the installation you need a MET as to reg 542.4.1. If you taking the 16mm from the head to the CU then your earth bar in the CU is now classed as your MET.

That 16mm is the earth conductor from the DNO's earth point. It would be like say on a TN-S system if a BS 951 was fitted to the sheath, you can not class that as the installtion MET, and I don't think you would take a bonding cable back to connect onto it, as that is external to the installtion. The same as the earth rod of a TT system. all these are external to your installation.

Not sure if I explained that to well lol but hope you get what I mean.

 

[Amp David]

So all main bonding conductors must be taken back to the same point then?

Looks like it'll be the CU then.

 

[tonys]

Malc

The job I'm on, we have a Main Earth Bar with a removal link (for testing) All the Main Bonding Cables Terminate here.

Main Earth 70mm, Main Bonding Conductors 50mm, Earths to Dis-Boards Via SWA Sheaths Connected to Main Panel Casing, which in turns Connects to Main Earth Bar.

Main Panel Connects to Main Incomer.

How many Main Earth Terminals/Bars now?

 

[Engineer54]

ONE ... the star point is that main earth bar where all the other earthing and bonding conductors you mentioned commonly connect too. It's exactly the same with the MET or the use of the CU as the MET.

As others have clearly stated, there can only be ONE common main earthing/bonding point, not TWO!!

 

[tonys]

Domestic example! One 4 way block is fitted adjacent to meter/fuse cut out. Electrically board connect their Earth Conductor, Consumer Unit Earth also connects with Gas Bond.

Water Bond goes into Consumer Unit. All Earths and Main Bonds are Labeled. All I asked is, what is wrong with that. The nic don't have an issue with it.

 

[malcolmsanford]

Is there a reason Tony why you want to do it this way?

If you fitted a main earth block with the DNO earth conductor, the CU CPC and then the gas bond connected to it, why would you want to connect the water to the CU earth bar mate as you will have the situation of bonds going to to different positions.

I don't have any of the NICEIC literature with me but how do they square away this out of interest?

 

[Amp David]

The only reason I would see for doing it is if on of the main bonds was a total pig to get back to the main intake to connect to your MET.

 

[tonys]

Malcolm

I don't want to do it, but Ive seen it done where someone as missed a redundant gas pipe or something and the earth bond was taken back to the block but the other bonds were in the dis-board, and as Amp David said pig times.

I was just wondering what people's opinions were, and you know I'm playing with big cables not the DIY stuff lol

 

[Engineer54]

Tony,

All the earthing bonds from say gas/water/oil pipes, Vent ducts, exposed structural steelwork etc,etc need to be connected at a common point (star point) That can be within the DB/CU, on a MET block, or as in your present installation, on a common earth bar.

Doing as you suggest, and having 2 such locations isn't necessarily going to make any difference to the effectiveness of the earthing and equal-potential bonds. But can make future testing and fault finding protracted to say the least. It has always been good working practise to have an installations main earthing/bonding cables connected in a common star configuration, not as you are suggesting in a delta or series linked system.

If you are stuck with a bonding cable that's been brought to the CU/DB instead of the MET/Main Earth Bar, where all the other earthing connections are located, why not thru crimp a suitable sized length of cable and extend it to the common location?? All in the world will then be put right!!! ...lol!!!

Edit.....

I don't think the NIC or any other body would be happy with having 2 METs, after all, what does the M stand for in the term MET??

 

[tonys]

Egin54

I ain't stuck with any cable that needs crimping, just asking a question on it. I rarely get involved with domestic now days, I done it for a few years on price to clear the mortgage (debt is not wealth) but I have seen it done and have watched an nic inspector take no interest.

Also seen plenty crimps floating around in ceiling, but I'm no longer interested or concerned what people get up to, got the QS tag off my back, so back to being an Electrician without a care in the world.

 

[Deleted member 26818]

From BS7671:
"Main Earth Terminal. The terminal or bar provided for the connection of protetive conductors, including protective bonding conductors, and conductors for functional earthing, if any, to the means of earthing."
Which is the MET, the bar in the CU where the CPCs are connected, or the terminal or bar (if any) provided by the DNO for connection to the installation earth?
To my mind the Main earth Terminal is where the connection to the main earth is made, be it a terminal provided by the DNO, the installer or the terminal on an earth electrode.
The bar in the CU, and any other bars that may be used are are Earth Marshalling Terminals used to gather conductors before a single conductor is then used for connection to the MET, or another EMT.
There is no requirement for the conductors that are required to be connected to the MET to be physically taken to the MET, just a means for connecting them there.

 

[tonys]

There is no requirement for the conductors that are required to be connected to the MET to be physically taken to the MET, just a means for connecting them there.

That's why I kept asking the question. Connection as in the meaning of continuity.

 

[Engineer54]

Marshaling bars (EMTs) are basically considered as common points of connection for a system. (ie cpc's of circuits within say a CU or other systems with multiple cpc's) A connection from those EMTs will then be taken to an MET as will the buildings main Bonding conductors thus creating an earthing system star point. The Reg's allow you to choose, where the MET is located such as the CU earthing bar, MET block, an installed or provided earthing bar, etc.

As stated above it has always been considered good working practise that an installations main Earthing conductors should be connected in a star configuration, a common point where the said main conductors can be easily individually tested or as a whole. Mixing main earthing and bonding conductors at various EMTs that are not associated with the system they are derived from, is not, and never has been considered a good practise... Even if it does provide continuous continuity!!

 

[malcolmsanford]

You are also combining a CPC with Bonding in one conductor. Though not prohibted in doing this you have to ensure that it is capable of doing both jobs if a fault occurs on the installation.

Like Engineer54 it is just down to good practice. You would expect to see the bonding cables at the MET and if you had one on there and another in the CU bar it just looks odd.

 

[tonys]

You are also combining a CPC with Bonding in one conductor. Though not prohibted in doing this you have to ensure that it is capable of doing both jobs if a fault occurs on the installation.

Taking a basic domestic, that's what happens if you take the main bonding into the dis-board. Adiabatic calculation takes care of that one and reference to GN8.

At the moment I'm on a job for a very large M&E out-fit and tomorrow their NIC QS is meant to be on site, and in the main switch room, there's an Internal Earth Bar in the main switch panel and also another Earth Bar mounted external.

So if you drop the link on the External Earth Bar to drop out the main bonding to the gas, water, lightning conductor, soil waste etc, there will still be parallel Earths running back to the main panel via all the SWA's what feeds all the flats and landlord dis-boards etc.

He will more than likely tell me to mind my own business, like when I queried the main bonding to the metallic boiler flues.

 

[Engineer54]

Tony,

It's very difficult to eliminate parallel earth paths in multi dwelling buildings, (or Any such large installation) as each dwelling unit is considered as a separate installation and as such requires the services within that unit to be bonded back to the units CUs MET.

There are ways around bringing these parallel earth paths back to the buildings metallic MDB on the SWA, but they tend not to be cost effective in today's climate of saving money at every turn. Now days it's just a matter of going through the motions and/or just ensuring that the various earthing conductors continuity throughout the installation is proved. The problems only show when testing the earthing systems, or when trying to find faults on the earthing system, ...then it can be a problem, that often never gets effectively solved!!!

 

[tonys]

Engin54

That's no different to what I was getting at earlier, this one is just a larger version. The main bonds on this installation do not go back to the MET, because its in the rear of the main panel.

So we have all the sub mains CPC's going back to the MET but not the main Bonds, they go back to a Earth Bar what is connected back to the MET via a Earth cable, do we agree lol.

Also I do understand what good practices are, so in this instance are you going to make allowances because it was an Engineers decision to do things this way lol

One more thing, its good for me to discuss stuff with an Engineer that way I keep learning more, that's why I enjoy a chat with IQ, hes quite good as well!

 

[Engineer54]

engin54

that's no different to what i was getting at earlier, this one is just a larger version. The main bonds on this installation do not go back to the met, because its in the rear of the main panel. well, first off i would always make the external system earth bar the met and not the mdb earth bar that is an emt to my mind. So in essence the opposite to how your installation has been designed. I always insist that metallic mdb, dbs (which most of them are) have insulated earth bar arrangements, so that electrical earths and frame earthing, remain separate until connected at the met. But, as i previously stated cost savings seem more important these days in the uk.

so we have all the sub mains cpc's going back to the met but not the main bonds, they go back to a earth bar what is connected back to the met via a earth cable, do we agree lol. no, see above. Nothing much you can do about those sub distribution boards bringing back bonding arrangements from the separate dwelling units via the SWA, not unless your prepared to spend some money, ...lol!!!

also i do understand what good practices are, so in this instance are you going to make allowances because it was an engineers decision to do things this way lol not at all, just facing the reality that things have changed in the uk and not for the better either. But i can assure you, that on projects that i have control of, ...things like this ''are'' taken into account, and as far as possible earthing conductors of all types/systems remain separated until they reach the met. I don't only deal with lv building earths but hv distribution earthing arrangements, as well as prime generation facilities and i suppose everything between too. ..lol!!

one more thing, its good for me to discuss stuff with an engineer that way i keep learning more, that's why i enjoy a chat with iq, hes quite good as well! we are all still learning, the day we stop learning is the day you stop working!! Even then you can't help but pick things up, from sometimes the most unexpected of sources or places.... I'm not always right, and if shown i've got it wrong, then i will be the first to admit it...

The problem is Tony, that we all see things on site that we would dearly like to change, we know that they can be done better/safer etc. But in the real world it usually just isn't going to happen. We just have to do the best we can with the materials and tools we have. I'm afraid "Good Working Practices'' are fast becoming a thing of the past, money rules supreme in this present day world climate....

 

[tonys]

The problem is Tony, that we all see things on site that we would dearly like to change, we know that they can be done better/safer etc. But in the real world it usually just isn't going to happen. We just have to do the best we can with the materials and tools we have. I'm afraid "Good Working Practices'' are fast becoming a thing of the past, money rules supreme in this present day world climate....

Engin54

At the end of the day I'm just an installer who gets his test kit out when I'm asked. To try and discuss things with Engineers on site is a waste of time, they are king pin in their world, so its a case of like it or lump it for people like me. I'm not to bothered though I'm content and happy in my skin and glad I have daughters who will be guided into the path of a good career which I will pay for

 

[Engineer54]

Engin54

At the end of the day I'm just an installer who gets his test kit out when I'm asked. To try and discuss things with Engineers on site is a waste of time, they are king pin in their world, so its a case of like it or lump it for people like me. I'm not to bothered though I'm content and happy in my skin and glad I have daughters who will be guided into the path of a good career which I will pay for

Have you ever considered that he knows exactly what your talking about, and knows that he doesn't have an answer for you?? He is also probably doing as he is told, and not how he would like to see things done!!

I hope those careers your guiding your daughters towards, are of a parasitic nature, they are the only professions left guaranteed to give you a Good and never ending income. Anything that makes a living off the backs and misfortunes of others, will never cease, and in the present day situation, more so than ever ...lol!!
No1 is Bankers and Solicitors and of course there derivatives.... hahaha!!!