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Hello Guys

I have a 200a 3-phase supply PME bolted to a large ryefield panel, the ryefiled panel then supplies 14 flats within the same building.

Each flat is supplied a 63a from ryefild via meters in the form of a 16mm 3core SWA cable.

The furthest away is flat 14 at around 25 meters, seeing as we are exporting the PME supply i would need a minimum 0.05 max between the main bonding in the flats and the MET at the origin (Ryefeild) because the CPC in the SWA is a combined CPC and main bond.

how can i calculate the R2 value alone as looking at table 11 OSG its R1+R2.. would i simply divide by two seeing as the line conductor is the same CSA.
 
Hello Guys

I have a 200a 3-phase supply PME bolted to a large ryefield panel, the ryefiled panel then supplies 14 flats within the same building.

Each flat is supplied a 63a from ryefild via meters in the form of a 16mm 3core SWA cable.

The furthest away is flat 14 at around 25 meters, seeing as we are exporting the PME supply i would need a minimum 0.05 max between the main bonding in the flats and the MET at the origin (Ryefeild) because the CPC in the SWA is a combined CPC and main bond.

how can i calculate the R2 value alone as looking at table 11 OSG its R1+R2.. would i simply divide by two seeing as the line conductor is the same CSA.
Do a long lead test an you will have r2
 
Thanks Cliffed... so your saying if i just look at table 54.8 will that be the neutral in the SWA sub mains of the neutral of the incoming main supply
 
Hi - it’s the size of the incoming DNO supply at the last point where it’s still a PEN conductor, if I’ve understood correctly. Hopefully it’s 50mm or less and you’re good with the 16mm (values from Table 54.8 as you say). The 0.05 Ohms thing is an urban myth :) .
 
Thanks Cliffed... so your saying if i just look at table 54.8 will that be the neutral in the SWA sub mains of the neutral of the incoming main supply
Exactly,could well be 25mm,for main bonding,also Main Earth should be sized accordingly,maybe for 200 amps 35mm,good luck.
 
The BNO should have the spec of the supply so you can determine the size of the N, if not a quick phone call to your DNO would be the way to proceed.
Your DNO will have a policy document for their requirements for protection for multi way distribution units (Ryefields etc), ask for a copy
 
I cant see why any bonding would be required internally to the flats? Any bonding would need to come from the ryfield/MET to water/gas/structural in prefumanly cellar/switchroom. As other have said, what is dno supply/tails?
 
The water and gas inside the flats are 10mm bonded ... the thing that I am quite confused about is the main bonds for the water and gas coming into the building is one huge 50mm cable.
Then inside the flats 10mm water and gas bonds

There are two main bonds?
 
Main bonding should be installed for each installation.
The installation in each flat is a seperate electrical installation and should have its own main bonding.

If they are being classed as a separate installation, then surely you would base the bonding conductor csa on the supply conductors for the individual installation?
 
Thanks Dave... so going with that and table 54.8, it states selection in accordance with the PEN conductor. So would I need to size the earthing arrangements for each flat according to the main PEN conductor, the PEN conductor at origin is 70mm which would render the CPC of the SWA too small at only 16mm to each flat
 
If they are being classed as a separate installation, then surely you would base the bonding conductor csa on the supply conductors for the individual installation?

No, the size of the bonding is based on the size of the DNO's combined neutral and earth conductor. Neutral current diverted via the bonding under fault conditions will depend on this, not on the size of the supply to each flat.

Ultimately for a job like this the DNO should be consulted.
 
No, the size of the bonding is based on the size of the DNO's combined neutral and earth conductor. Neutral current diverted via the bonding under fault conditions will depend on this, not on the size of the supply to each flat.

Ultimately for a job like this the DNO should be consulted.
Yea that’s how I read it,if you export Pme,then you need to ensure its requirements.
 
No, the size of the bonding is based on the size of the DNO's combined neutral and earth conductor. Neutral current diverted via the bonding under fault conditions will depend on this, not on the size of the supply to each flat.

Ultimately for a job like this the DNO should be consulted.

Agreed, but surely this is why the 50mm bond to structural steel from the ryefield is in place. Also, any of the diverted neutral current from the PEN conductor in fault would also be shared across a number of bonds due to the duplication across units?

In any event I suspect it's all completely hypothetical, if it's a new build with individual gas and water metering, there are unlikely to be any extraneous parts, and if it's an older block with common risers in Iron, then the 'main' main bonds from the ryefield would take care of any stray currents.

In reality, has anyone ever worked on a flat with a 50mm bond anchored to the stopcock?
 

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