Earthing conductor and main bonding conductor clarification wanted please.

[SYKRAPS]

To make it clearer about my job (heaven knows why I should) in my earlier post at my job there was communal heating, cooking and washing and therefore no need for every flat to be bonded by its own rights as there was no gas and water in each flat...........................

 

[spark 68]

It is in GN8 mate, this tells us each flat is to be considered as a seperate installation, this also goes for HMO's (houses of multiple occupancy), bedsits and the like, and it refers you to reg 411.1.3.2 for the electrical definitions, I have posted the relevant info. on the forum before (pages from GN8).

There have been some rather longwinded posts on here before also regarding this subject.

It is so each flat has it's own equipotential zone, and as BS7671 requires each installation to have main bonding conductors, GN8 elaborates on this, and specifically says this applies to multi occupancy buildings and classes each flat as a seperate installation and also elaborates on the definitions given in the reg number above.

Edit:, I was not having a dig at anyone, just posting the information which some people may find informative and useful, as not everyone has GN8, even GN8 itself states that the regs regarding this are not clear, and are often misunderstood/misinterpreted.

 

[flyingsparc]

Many thanks to all for the recent replies.

Yes each flat has their own local CU.

When you ask - how many water stops and gas valves does the property have, do you mean the block of flats as a whole or the flat in question? Either way the flat has one water stop, I don’t know about the other 3 flats (they are all privately owned) but I would expect to find one in each flat, and one or four where the water enters the block. With the gas valve/meters there is one per flat, so four in total.

I will have another look for the water stops tomorrow, would the amount of water stops in the block affect the answer to my question about the 6mm earthing conductor?

Another point worth mentioning is that from the DNO head to each meter and onto each switch fuse are supplied via 10mm CSA line and neutral conductors.

One other point I would like to clarify is that it has been suggested I could run in a 10mm conductor alongside the 16mm t&e. I thought there was a regulation (can find it though as yet) about if running parallel conductors that they should be the same CSA? Don’t know why that’s in my head though!?

Thanks again.

 

[MDJ]

I would certainely run a 10mm2 earth wire with the 16mm2 Twin and Earth, good practice IMO, if you can aford to do so within your quote you may as well.

 

[johnboy6083]

The minimum size of Bonding conductor is 6mm for TNS, and 10mm for PME. Its common practice and the diargram in the front of the OSG that has everybody beleiving that a main earthing conducotr has to be 16mm min, and the main bonding 10mm min. Thias isnt the case. A main earthing conductor for a tns can be sized by selection from table 54.7, or calculated vie the adiabatic. The main bonding has to be half of this ( well it says half of the required size. Even if somebody has used a 35mm as a main earth, if your calcs say it could be a 16mm, then a 10mm bond will do. Useful to know when working in older installations)
For PME you have to go with the requirements of your local DNO, and a far as im aware, theyre usually happy to go with the table in BS7671.

 

[Amp David]

GN8 is a great read for this very subject.