# PME supply block of flats

Discuss PME supply block of flats in the Electrical Forum area at ElectriciansForums.net

#### chris day

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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.

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#### ChrisElectrical88

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Calculate R1 R2 and divide by 2 as it is exactly the same conductor size as you suggest.

#### Tony Reidy

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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.
Do a long lead test an you will have r2

#### cliffed

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The resistance is not the issue here,the main bonding must be sized accordingly to the Neutral size.

#### Strima

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Can you show me where it states maximum of 0.05 ohms for bonding?

#### chris day

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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

#### Wilko

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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 .

#### Bellendian

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Just playing devils advocate for a second, but what is it that requires main bonding in each of the individual flats?

#### cliffed

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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.

#### mhar

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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

#### bigspark17

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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?

#### chris day

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DNO tails are 70mm 3- phase and neutral on a 200a bs 1361 fuse.

#### chris day

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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?

#### davesparks

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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.

#### Bellendian

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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?

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