Location of Main Equipotential Bonding

[Dalimo]

Evening All,

Gone to look at a rewire of a flat. Communal cupboard is a 3 phase supply, with 3 cut outs for each of the flats one of which is split for the landlords CCU.
TN-S system, each flat has an old KMF switch which in turn feeds a 16mm twin and earth cable, approx 1970's build.
Main earthing terminal in the cupboard is a 4 way block:
Earth from supply in 1 terminal, flat 1 on its own, flat 2 on its own, flat 3 doubled up with landlords CCU earthing conductor.
The flat in question has MEB to its incoming gas and water main in 10mm and goes back to the earth bar in the existing CCU (an old Wylex BS3036), which is in turn a 6mm supply (from the 16mm twin and earth).

The consumer unit is being moved to another location, and I have suggested a 16mm SWA, with a switch fuse unit in the communal cupboard.

What are people's preferred methods as its a TN-S system:
Main Bonding to new CCU or,
Main Bonding to MET?

However when I get to the MET I have only 1 terminal spare.

If the consensus is to run it back to the MET, is it better to try and arrange with the other two flats to switch them off and put a bigger block in for the all 3 flats, landlord CCU and my MEB conductors,
or put a link in from my 'spare' terminal to a new earth block for the 16mm SWA and MEB conductors.

Its not a question of costs, just want it to look nice, neat and what my options are if the other flats so NO, we don't want to be switched off.
What are my responsibilities with regards to their supply cable if they say OK, testing wise?

Any advice would be helpful.

David

 

[Dalimo]

Its going to be a 3 core SWA.

David

 

[westward10]

I would personally contain them at the CU in the flat.

 

[Strima]

Are the incoming water and gas services one supply for all the flats or separate for each?

 

[buzzlightyear]

However when I get to the MET I have only 1 terminal spare.

how many ways is that then.

 

[Dalimo]

Not sure, the communal cupboard was very bare, no other services, no other meters. The clients showed me the gas meter (in the flat) but as they have just bought it didn't know where the water meter was.

The other flats supplied from the communal cupboard exactly the same setup,,,,just the 16mm twin and earth, no sign s of any other bonding anywhere?

 

[Dalimo]

Just to clarify buzzlightyear, the MET block is 4 way, the 'spare' terminal is achieved as I will be removing the 16mm twin and earth cable and replacing it.

 

[Strima]

I'd test the services back to the MET and see if they need bonding back to there, if not I'd just bond to the CU in the flat to maintain that as an equipotential zone.

 

[Strima]

Just to clarify buzzlightyear, the MET block is 4 way, the 'spare' terminal is achieved as I will be removing the 16mm twin and earth cable and replacing it.

A couple of quid will get you an 8 way block.

 

[buzzlightyear]

where is the DNO ,meter.

 

[Dalimo]

The meter is in the communal cupboard where the 16mm T + E are terminated into the KMF's.

Strima, I agree an 8 way block is pence but do i replace the 4 way one and in doing so temporarily remove the earth from the other flats? Or put a link in between the MET and a new 8 way block, which then isn't the MET.

 

[Dalimo]

Of course, if i do replace the earth bar then i will need to switch off the other flats, and arrange for that and then what are my responsibilities if i mess around with it and find a fault?

 

[buzzlightyear]

isolate all flats in the communal area, when you altering the sub supply, buy telling the people that you are doing work ,and give them a time you are switching off .could not be clearer then that.

 

[westward10]

I'd test the services back to the MET and see if they need bonding back to there, if not I'd just bond to the CU in the flat to maintain that as an equipotential zone.

Equipotential zone, what Regs you working to.

 

[polo1]

I think ( as far as the MET is concerned), just looping off the “spare” terminal you will create is the least problematic approach. You don’t want to be involving other occupiers if you can avoid it.

 

[Dalimo]

Had an idea......each of the CPC's is about 10 inches long. Was thinking unscrew the block from the backer board but leaving all the conductors still connected, bend over each of the conductors and they are effectively the size of a 12mm conductor slip each of these doubled up conductors into a terminal of an 8 way block.
Still left the original Met but slipped a new one in front of it without having to disconnect anything and giving me the extra ways?

 

[westward10]

Becoming a bit over complicated this.

 

[buzzlightyear]

Had an idea......each of the CPC's is about 10 inches long. Was thinking unscrew the block from the backer board but leaving all the conductors still connected, bend over each of the conductors and they are effectively the size of a 12mm conductor slip each of these doubled up conductors into a terminal of an 8 way block.
Still left the original Met but slipped a new one in front of it without having to disconnect anything and giving me the extra ways?

and if their is a fault in one of the flats ,holly F77k !

 

[Dalimo]

Tell me about it, think I'm going to do a mix of testing with the wander lead, working out what is what and bonded to what. At the end of the day if I need to arrange switching off the neighbours so be it.
Thanks everyone for your time, glad I am mulling it over now rather than on site on a Friday afternoon.
And just to make things even more fun with it the hallway, corridor and walls are concrete!
Time for a suicide price.

 

[mhar]

GN8 details where you should bond and the DNO will have a policy document which will be part of your supply agreement.

You should bond all incoming services (that test as extraneous) to a building earth marshalling point at the origin. The size of bond required is related to the size of the supply N.

Additionally, within each unit (individual equipotential zones) you must bond as you would do in any dwelling . However, unless you have a seperate earthing conductor to each flat to supplement the cpc in the 16mm t & e you will be undersized and you will need to seek guidance from your cps operator on how to proceed. The new 16mm swa you propose would be fine