Cu Change Main Earth HELP!

[Engineer54]

My thinking is that to be 100% compliant I could TT CU even though Ze obviusly higher but all RCD protected anyway and keep MET and bonds where they are?

You're joking now arn't you?? ....Please say your joking!!!

 

[telectrix]

putting eng's post into plain english......... if it ain't broke, don't fix it. LOL. :75:

 

[mcl]

You don't say how many holiday dwelling were talking about, but at the main DNO intake there should be a series of Switch Fuses or a Ryefield panel that supplies these holiday dwellings. The main earth conductor off the PME head will need to comply with PME requirements to the MET in the intake building/room. (which may require a larger conductor size than 16mm, depending on the the actual size of the DNO supply) The supplies away from this building, to the respective dwellings, are in effect distribution circuits. The individual Dwellings MET's are actually EMT's, there can only be One MET and that is always at the origin of the supply.


Personally i would have run in 3 core 16mm SWA from the intake position to the dwelling units, but you have what you have and that's a 10mm Earthing conductor. So check if it meets all the criteria, if so, it should be fine.

Hi
Thanks for advice. There is 6 cottages, but all have seperate western power fuses and separate meters all in one building. The appears to be no MET here. The tails and Earth travel 30m to the CU. It appears to be the same with each of the others. Although there are 6 cottages together, they are all seperate supplies and all cottages owned by different people. Therefore I am sure the MET is at the CU? I know it sounds stupid to TT a supply when it is PME but if I the main eaarth needs to be 16mm and it cant be done without digging 30m then is it not an option?

 

[Clive P]

Hi,

The MET ( cable sized according to incoming supply ) should be at your intake position, ie where the meters are installed, and the 10mm cable with the 16mm tails is your supply to your CU at the Barn. At the Barn you would have installed your EMT. Just think it as being a normal install with long tails.

Regards.

 

[D Skelton]

Unless there is an extremely high or extremely low PFC, what on earth is wrong with a 10mm main earth on a 60A PME?!?

Required tail size is 16mm, therefore main bond will be 10mm. The main earth is sized according to the bonding conductor. Ergo sum... 10mm main earth.

I wouldn't entertain using any higher than 10mm for the main earth for any supply up to and including 100A regardless of its type (PFC permitting).

 

[Engineer54]

Hi
Thanks for advice. There is 6 cottages, but all have seperate western power fuses and separate meters all in one building. The appears to be no MET here. The tails and Earth travel 30m to the CU. It appears to be the same with each of the others. Although there are 6 cottages together, they are all seperate supplies and all cottages owned by different people. Therefore I am sure the MET is at the CU? I know it sounds stupid to TT a supply when it is PME but if I the main eaarth needs to be 16mm and it cant be done without digging 30m then is it not an option?

Sorry i can't envisage the set-up your describing, any chance of a photo or two of the intake building room set-up and one of the cottage supply position??

Forget any notion you may have, of degrading your earthing system, from what you have at the moment!! It not only sounds stupid, it IS stupid!! lol!!

Thought you said the supply cable to the cottage was ducted, so why would you need to excavate?? What type of conductors/cable is being used in this duct??

 

[Engineer54]

Unless there is an extremely high or extremely low PFC, what on earth is wrong with a 10mm main earth on a 60A PME?!? Pretty much agree with that...

Required tail size is 16mm, therefore main bond will be 10mm. The main earth is sized according to the bonding conductor. Ergo sum... 10mm main earth. ...other way round!!

I wouldn't entertain using any higher than 10mm for the main earth for any supply up to and including 100A regardless of its type (PFC permitting). I don't totally agree with that statement

I just think this is a strange distribution system, from what i can make of it so far!! lol!!

 

[D Skelton]

Eng on a PME system the main bond is sized according to the supply neutral. The main earth then has to be sized according to the bonding conductor (542.3.1).

PME; size the bond then the earth.
TN/TT; size the earth then the bond.

Out of interest, why don't you 'totally agree' with my last statement?

 

[Engineer54]

Eng on a PME system the main bond is sized according to the supply neutral. The main earth then has to be sized according to the bonding conductor (542.3.1).

PME; size the bond then the earth.
TN/TT; size the earth then the bond.

Out of interest, why don't you 'totally agree' with my last statement?

Going to bed now mate, (2.30am here) get back to you tomorrow sometime!!

 

[telectrix]

it is wrong way round. the bonding conductor/s are sized according to the size of the required main earthing conductor. and while we're on it, what is the reg. no. taht says on a pme system it's got to be 16mm.

 

[7029 dave]

If the me is 10mm on a 60 amp main cut out I would leave it, if as you say all plots have their own fused cut outs, no multie ways anywere ie ryefield units?,but if that was the case you would have a met at the supply intake.without a pic its a bit hard good luck.

 

[D Skelton]

Going to bed now mate, (2.30am here) get back to you tomorrow sometime!!

No worries buddy

it is wrong way round. the bonding conductor/s are sized according to the size of the required main earthing conductor.

Its not the wrong way round Tel, sorry pal. See 542.3.1

and while we're on it, what is the reg. no. taht says on a pme system it's got to be 16mm.

There isn't one??? Why?

 

[telectrix]

Its not the wrong way round Tel, sorry pal. See 542.3.1

don't disagree there, basically the earthing conductor must not be less than 10mm, but that's not to say it has to be >10mm.

 

[D Skelton]

Its not the wrong way round Tel, sorry pal. See 542.3.1

don't disagree there, basically the earthing conductor must not be less than 10mm, but that's not to say it has to be >10mm.

No of course not, I don't believe I said that did I?

My point was that on a PME system you size the (minimum size of) main earth by the main bonding conductor. That's all

 

[tony mc]

Post 3 has answered your question and delete the need for mentioning anything about the size of the Earth on the EIC !