Another "exporting PME post"...

[dmcturk]

I have a situation whereby a new build property has had a green electrical cabinet installed at its boundary, and a new 3ph PME supply installed.
There is a 4c 25mm SWA from here to the detached garage, which will house the plant room (3ph ground source heat pump, 3ph PV inverter), and then another 4c 25mm SWA from the garage to the house.
Incoming water is a new polypipe, and there is no gas/oil on site.

Is there anyway to use the PME, or will I need to TT each site??

 

[HandySparks]

I take it that the only earth conductor is the SWA armour?

 

[Deleted member 26818]

What are the 4 cores?

 

[dmcturk]

What are the 4 cores?

Yes, L1,2,3+N

 

[westward10]

Is all internal pipework going to be plastic.

 

[bigspark17]

Is 3 phase required in the house? Why not install 5c or run supplementary earth along side swa to futureproof any alterations? Is there any exposed structural steel work that is extraneous in house of garage?

 

[Deleted member 9648]

Is 3 phase required in the house? Why not install 5c or run supplementary earth along side swa to futureproof any alterations? Is there any exposed structural steel work that is extraneous in house of garage?

Sounds like the cables are already installed.
As long as there are no extraneous parts requiring main bonding in either the garage or house then the PME earthing system can be used.

 

[Deleted member 26818]

Sounds like the cables are already installed.
As long as there are no extraneous parts requiring main bonding in either the garage or house then the PME earthing system can be used.

No.
The requirements for bonding conductors also apply to the main earthing conductors where PME conditions apply.

 

[dmcturk]

To my knowledge all pipework in the house will be plastic, but plant room will probably contain copper.
No exposed steels, all rsj's to be boxed in.

House is 3ph in order to to benefit from the 3ph solar PV, and keep it all balanced.

 

[Deleted member 9648]

No.
The requirements for bonding conductors also apply to the main earthing conductors where PME conditions apply.

Thanks for that.

 

[westward10]

If main protective bonds are required then the armour is inadequate to support the bonding. It is assumed a switch fuse disconnector is to be used at the source of supply, the earthing conductor for this can be selected from Table 54.7 without calculation unless the DNO prescribes otherwise. From here the armour can be used as the cpc (assuming bonding is not required), you can verify the suitability of the armour to be used as a cpc using 543.1.3 and the adiabatic equation, it is not likely this will indicate the armour is not suitable. Remember if bonding is not an issue and a switch fuse connector is in place the armour is a cpc and not an earthing conductor.

 

[Deleted member 26818]

"542.3.1 Every earthing conductor shall comply with Section 543 and, where PME conditions apply, shall meet the requirements of Regulation 544.1.1 for the cross-sectional area of a main protective bonding conductor." (Note quotation marks)
Irrespective of whether there are extraneous-conductive-parts or bonding conductors, the requirements are for the CSA of the main earthing conductor to be determined by use of Table 54.8, where the earthing conductor is other than copper, the CSA shall afford equivalent conductance. (Note lack of quotation marks)

 

[westward10]

Put a switch fuse disconnector in place it becomes a cpc, my post was based on a non requirement for main protective bonding. The only earthing conductor is to the switch fuse disconnector.

 

[Wilko]

Hi - isn't it a bold move to build a house with no bonding and no possibility to provide it? I'm back with BigSpark #6

 

[Wilko]

On the earthing conductor bit, I've been struggling with this. Opening GN8, page 37, it reminded me "the earthing conductor of an electrical installation is the protective conductor that connects the means of earthing (DNO in this case) with the MET of the installation ... There is only one such conductor in each installation."

So my thoughts are : Assuming the cutout, service fuse and meter are in the garage, then the MET is likely there and the cable linking MET to cutout is the earthing conductor for the whole site. Since we know the DNO incoming is 25mm, the earthing conductor could be selected as 16mm, being the bigger of Tables 54.7 and 54.8, if I've understood correctly. Then the cable from garage to house needs to provide CPC and protective bonding conductor (if required). CPC could be selected from Table 54.7 to be the adiabatic equivalent of 16mm copper, and for this SWA armour is ok. The protective bonding conductor (if required) could be selected from Table 54.8 to be the conductive equivalent of 10mm copper, which the armour does not meet.

Please let me know if I've stuffed this

 

[westward10]

Yep I am with you on that. My notion above is that a switch fuse disconnector is installed then the armour does become a cpc, if not then I would view it as an extension of the earthing conductor. This is all assuming bonding is not required and then the armour only need be sized for its adequacy as a cpc in relation to the protective device at the switch fuse. If bonds are required this is irrelevant.
It is the 4 core 25.0 swa I am a bit confused with, I am assuming it is coming from the DNO source by way of said switch fuse.

 

[westward10]

"542.3.1 Every earthing conductor shall comply with Section 543 and, where PME conditions apply, shall meet the requirements of Regulation 544.1.1 for the cross-sectional area of a main protective bonding conductor." (Note quotation marks)
Irrespective of whether there are extraneous-conductive-parts or bonding conductors, the requirements are for the CSA of the main earthing conductor to be determined by use of Table 54.8, where the earthing conductor is other than copper, the CSA shall afford equivalent conductance. (Note lack of quotation marks)

I am not sure if you are being deliberately obtuse, again or whether you genuinely do not understand!

 

[dmcturk]

Yep I am with you on that. My notion above is that a switch fuse disconnector is installed then the armour does become a cpc, if not then I would view it as an extension of the earthing conductor. This is all assuming bonding is not required and then the armour only need be sized for its adequacy as a cpc in relation to the protective device at the switch fuse. If bonds are required this is irrelevant.
It is the 4 core 25.0 swa I am a bit confused with, I am assuming it is coming from the DNO source by way of said switch fuse.

The DNO supply comes into the green cabinet, and within this cabinet there is a 4w 3ph dist board.
The 4c 25mm SWA runs from here to the garage, to another 3ph dist board, then from here to the house.
There is a duct from cabinet to garage, so an additional bond could be pulled in, but as I say, the incoming water is plastic.

 

[westward10]

The DNO supply comes into the green cabinet, and within this cabinet there is a 4w 3ph dist board.
The 4c 25mm SWA runs from here to the garage, to another 3ph dist board, then from here to the house.
There is a duct from cabinet to garage, so an additional bond could be pulled in, but as I say, the incoming water is plastic.

Okay got you now.

 

[Leesparkykent]

For the sake of it I would of probably pulled in a 16mm green and yellow at the same time.