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?