Main bonding for flats scenario.

[Ian Speirs]

Hello everyone. I have a fuseboard change to do at the weekend, haven't seen it yet but have been told its a small flat in edinburgh. Will prob have to upgrade the earthing aswell. My question is this, If all the flats are sub mains from the main incommer on ground level and the main water is bonded at this point. would all the flats still require bonding between flat db and flat incomming water pipe. ?:|

 

[ianmacd]

The MET is the first Earth Terminal after the head so if there is only one head and the MET is there and has bonding of the correct size and the Earth from the MET to the Earth Terminal in the DB is the correct size then I would not look at bonding again.

That assumes there is only one head and one stop valve for the water. If there are seperate 'stop *****' in the flats then they should be bonded the other side of them and should be bonded back to the MET. Same goes for if there is more than one head but then you have more than one MET too (one per installation).

In summary:

One head and one stop cock - one MET and one Bond just as if DB's were in the same house

Multiple heads one stop cock - MET is in DB and indevidual bonds down to near stop cock

One head and multiple stop ***** - Bonding on customer side of stop ***** back to MET (first Earth Terminal after head)

Multiple heads and stop ***** - Bonding on cmr side of stop cock back to MET per installation. Met would most likely be in DB.

Think you need to find out if there is more than one head and stop cock.

 

[AAAMUSEMENTS]

Just wondered what the thinking was behind bonding above each stopcock? Trying to get my head round it.

 

[batty]

May also depend on what supply pipe is if its plastic to main in flat and then copper inside you would need to bond on consumer side of stopcock in flat although some may disagree with this.

 

[sellers]

As batty says! Test between the incoming earth at the flat and the flat stop cock. If you havent got 0.05ohms or less then I would bond. (I think its 0.05 someone please correct me.)

 

[Ian Speirs]

Thanks for the replies so far, Was gonna check if it was

0.05ohms between flat met and water pipe, but still was unsure if i should run one anyway. belts and braces. I guess i will decide once i get there, just trying to cover all areas before i turn up on sat.

 

[ADS]

As batty says! Test between the incoming earth at the flat and the flat stop cock. If you havent got 0.05ohms or less then I would bond. (I think its 0.05 someone please correct me.)

It's a lot higher than that to test if metalwork is extraneous and needs bonding - 0.05 ohms is the figure that the resistance of your bonding shouldn't exceed.

 

[ADS]

Hi Ian,

If you are to treat each flat as a seperate 'building' and the water/gas pipe-work is common to each building, then the guidance is that the pipework is bonded at it's entry to each building (flat) back to the MET.

Now, although this is aimed at seperate buildings, I think it could be applied here and therefore, I would bond in the individual flats.

After all, you have no idea of the routing of the pipework and whether it coulld possibly re-introduce an earth potential to one of the flats.

The other thing to take into account is that, if it weren't bonded in one flat, it could introduce an earth fault potential to that flat from the flat below.

I think this is the more serious consideration, so I would bond

 

[binky]

Ok slightly different scenario - one incoming water supply shared between flats with no visible stopcocks within the flats, but separate gas supplies and obviously separate electric supplies fed from Switch fuses.

 

[ADS]

Ok slightly different scenario - one incoming water supply shared between flats with no visible stopcocks within the flats, but separate gas supplies and obviously separate electric supplies fed from Switch fuses.

All got to be bonded back to the MET

Shared water supply could introduce an earth fault potential into one flat from another.

Seperate gas supplies could introduce earth potential into flats.

How they're supplied doesn't really matter.

 

[Mark2spark]

My initial reaction is every flat is a seperate dwelling, so each needs their own bonds.

 

[binky]

Ok, given separate supplies for gas and water at main incoming point, with MEBs to gas and water at incoming point. If fitting a dual RCD CU would you consider it necessary to run additional bonding to flat given that supplementary bonding is no longer required and to what purpose???(Electrics are through switch fuse, and therefore only on 6mm earth, supply is TN-S). Just for the record, I've always run additonal 10mm bond back to consumer head in the past, although many would argue that 6mm CPC is adequate (by adiabatic equation) given supply from switch fuse, with any bonding from within the flat being back to CU in flat, not MET at incoming point.

 

[sparkytim]

Checked the Essential Guide on this one,

Each seperate installation i.e. Flat has its own Bonding to ITS MET and the Main Incoming position has its own Bonding to ITS MET.

No further interconnection Bonding required.

 

[ianmacd]

Checked the Essential Guide on this one, Each seperate installation i.e. Flat has its own Bonding to ITS MET and the Main Incoming position has its own Bonding to ITS MET.

No further interconnection Bonding required.

That assumes each flat has a separate supply and not a common head and common MET.

 

[ADS]

That assumes each flat has a separate supply and not a common head and common MET.

I agree

 

[sparkytim]

:Blushing Yes have had another look.

Example shown is were DNO brings supply into service head position and then takenup to Meter in each flat.

"The supply arrangements may vary from (that) For example the meter operator's metering equipment may be grouped together at a common location. The principles of application of reg 411.3.1.2 still apply"

Another topic deals with interconnected services to several installations and this makes clear the Bonding should be interconnected between all METS. Usally this will be achived by ensuring the CPC of the Distribution circuit is adequate. NO seperate Bonding conductor required if size of CPC is equal to size of Bond required i.e. for PME (their term used not mine) 10mm CPC for 35mm Incoming nuetral.

 

[Ian Speirs]

Hi guys, thanks for all the input, Just a Quick update, Could not get access to location where main incommer from street entered the building. In the flat there was no bonding to incoming water pipe, so bonded it myself. Quite close to consummer unit so quite convenient. On another note though, when testing existing wiring i found the bathroom fan was on the lighting circuit, but the run on timer was on its own circuit so required 2 fuses to be pulled to isolate. No fan switch isolator either, rectified now though. Happy customer wants repeat custom now. :^O

 

[sparkytim]

Hi Ian glad the job went ok, its good to leave behind a happy customer

( I find doing a good job of cleaning up works wonders even if the Job itself didn't (Should have put that in Tips and Tricks)) :^O

So just for interest sake was the Meter postion in the Flat?

 

[Ian Speirs]

Yes, meter was in the flat, dual tarriff. op night storage heating in the flat, had to remove and re position the op board to make room for my new one. bad day explode