Sizing of CPC and bonding conductor

[novolts]

Hi Guys
I have been asked to quote to install a MET for a TN-C-S system and I could do with some advice please
I can't get into determine the size of the conductors as I cant switch the power off to open up the main panel
What I did was measure the circumference of the SWA it was 214mmm I divided this by 3.14 this came out to 61.8mm
diameter,I cross referenced this with cable manufacturers data sheets and the condutors are 300mm( 4 core SWA )
if my calculations are correct then the CPC would need to be 150mm and the bonding conductor 50mm
I found a label stating that the Ze was 0.03 ohms
Am I on the right lines or should chuck it all in and try and get a job at my local supermarket stacking trollies
thanks to all
kind regards
John

 

[telectrix]

price it at that but add a caveat that price is subject to verification of the line condictor size.

 

[novolts]

telectrix
thank you for your reply much appreciated
novolts

 

[SirKit Breaker]

Am i losing the plot here or have i misread something. When a TNCS system is installed, the supplier usually installs a main earthing terminal next to the neutral of the supplyhead, and connects it with the appropriate sized main earthing conductor. You then connect your installation to this using the same size earthing conductor and terminating it in your DB earth bar. Why have you been landed with the job of installing the supply Main Earthing Terminal, which you can't do because you are not allowed to open up the supply head to connect it up.

Confused.com.................Howard

 

[novolts]

SirKit

The installation is 32 years old, there has never been a MET in the installation, the gas pipe is bonded by a 16mm bolted to the metal work of the main panel,the means of earthing the main panel is from the armour of a 4 core 300mm SWA from the metering panel in the switchroom

I have taken on board your comments I will pass these to the senior electrical engineer of the company I work for who visited the site with me,he then proceeded to instruct me "to get on with
it"
thank you SirKit for taking the time to read my post
novolts

 

[pepparz]

SirKit

The installation is 32 years old, there has never been a MET in the installation, the gas pipe is bonded by a 16mm bolted to the metal work of the main panel,the means of earthing the main panel is from the armour of a 4 core 300mm SWA from the metering panel in the switchroom

I have taken on board your comments I will pass these to the senior electrical engineer of the company I work for who visited the site with me,he then proceeded to instruct me "to get on with
it"
thank you SirKit for taking the time to read my post
novolts

sounds to me like your engineer isnt much of a engineer and is passing the buck hoping you know what to do.
Good luck.

 

[GLENNSPARK]

Am i losing the plot here or have i misread something. When a TNCS system is installed, the supplier usually installs a main earthing terminal next to the neutral of the supplyhead, and connects it with the appropriate sized main earthing conductor. You then connect your installation to this using the same size earthing conductor and terminating it in your DB earth bar. Why have you been landed with the job of installing the supply Main Earthing Terminal, which you can't do because you are not allowed to open up the supply head to connect it up.

Confused.com.................Howard

no howard.

Main earthing conductor is not the distributers responsibility.

 

[pepparz]

think he means earthing conductor, not main earthing conductor.

 

[Engineer54]

SirKit

The installation is 32 years old, there has never been a MET in the installation, the gas pipe is bonded by a 16mm bolted to the metal work of the main panel,the means of earthing the main panel is from the armour of a 4 core 300mm SWA from the metering panel in the switchroom

I have taken on board your comments I will pass these to the senior electrical engineer of the company I work for who visited the site with me,he then proceeded to instruct me "to get on with
it"
thank you SirKit for taking the time to read my post
novolts

Maybe you should point out to this Senior Engineer, that the armouring of a 4 core 300mm SWA cable doesn't meet with CPC compliance, let alone also providing for main bonding connections of an installation... A suitably sized seperate earthing conductor is needed, before doing anything else!!

 

[novolts]

Hi Engineer54
Thank you for your reply
I wanted to be sure of the facts before speaking to the " Senior Engineer " that's why I am quoting for a 150mm CPC & 50mm bonding conductor and MET & clear identification of all bonding conductors
kind regards
novolts

 

[Deleted member 26818]

32 years old, most likely 6mm bonding conductors.
Unless PME conditions applied, then there was no requirement for the main earth conductor to be the same size as the bonding conductors.
Easiest way to determine the required CSA of the main earth conductor, is to conduct the a diabetic equation.
In most instances, 10mm will be sufficient for a supply up to 100A.
Remember that there may be specific requirements for the DNO.

 

[novolts]

Thank you spinlondon
I can't get access to the DNO's cutouts that is why I am erring on the side of caution with 150mm cpc and 50mm bonding conductor as I do not want to the chance and quote for a cpc and bonding conductor that could be the wrong size
kind regards
novolts