Concentric cable & EICR

[SUNRAY]

I've been out today to look at a friends rental EICR for an opinion.
To put it into perspective it is the 4th EICR/PIR in 4 years and the first 'failure'.
1 RCBO fails tests - C2, my Robin puts it right near the time limit so nearly fair fault code. While there I moved the spare to replace it.
The feed from meter & fused switch is concentric cable on cable tray in electrical riser - C2. All 12 properties across 3 floors are fed the same way.

Personally I don't see a problem with this and officially the tenant doesn't have access to the 'electric intake cabinet' (steel enclosure with 2 plastic panels to read meters) or 'services cupboards' (riser) although only secured with Triangle panel/meter box key and standard doorbolt key.

Any other opinions?

It took some finding but I recalled a picture of something a little while back
https://www.diynot.com/diy/threads/too-many-circuits.557695/ post 14

EDIT: I forgot to say the con terminates in an isolator with 2 links, no fuses, then tails to CU.

 

[Adam_151]

Concentric or Split concentric?

If it really is concentric, then it is a a C2, unless clearly on the DNO/BNO side (i.e. before utiltity company meter) as ESQCR does not allow N and E combined on customer side

If its split concentric then its fine, but must be treated the same way as any other PVC/PVC insulated and sheathed cable i.e. you can't class it as an earthed metalic cover and chase it in the wall without a 30mA RCD, or bury it between buildings

 

[SUNRAY]

Concentric or Split concentric?

If it really is concentric, then it is a a C2, unless clearly on the DNO/BNO side (i.e. before utiltity company meter) as ESQCR does not allow N and E combined on customer side

If its split concentric then its fine, but must be treated the same way as any other PVC/PVC insulated and sheathed cable i.e. you can't class it as an earthed metalic cover and chase it in the wall without a 30mA RCD, or bury it between buildings

Ahh that's a very good point, it is not being used for combined neutral and earth but the multiple neutrals are all black. for a concentric cable it hadn't occurred to me it would be bare wires. I can't see the cable butt (to see if the bares are cut off) as it's enclosed in a heat shrunk boot and the feed end is inside a sealed switch which I didn't want to cut.

There is an earth bar in the riser with a decent cable ~95/120mm² which continues up, with a 16mm² to each flat and a number of other bonding wires; water, gas, staircase, TV distro etc.

EDIT: Slight amendment to my OP the con terminates in a isolator beside the CU and tails between them.

 

[flameport]

Concentric doesn't comply with BS7671, however it could only be C2 if it was 'potentially dangerous'. As it's fixed to tray in a riser, risk of damage to it is minimal.
Non-compliance with BS7671 doesn't automatically mean dangerous.

There are plenty of properties which have that arrangement, mostly where the internal cabling was done by the DNO or electricity board when the property was built, and subsequently the ownership of the cables has changed.
A whole street of 1980s houses near here has it - concentric from a meter cabinet outside, under the floor, and appears under the stairs into a red cutout next to the consumer unit. Same with another block of flats built around 2000, meters in the basement, concentric to a cutout in each flat.

If any code must be given, C3.
However considering that just relocating the meter from one end of the cable to the other would make it outside of the scope of the EICR, even C3 seems unnecessary.

 

[Adam_151]

Ahh that's a very good point, it is not being used for combined neutral and earth but the multiple neutrals are all black. for a concentric cable it hadn't occurred to me it would be bare wires. I can't see the cable butt (to see if the bares are cut off) as it's enclosed in a heat shrunk boot and the feed end is inside a sealed switch which I didn't want to cut.

There is an earth bar in the riser with a decent cable ~95/120mm² which continues up, with a 16mm² to each flat and a number of other bonding wires; water, gas, staircase, TV distro etc.

I wonder why they ran a separate earth rather than using the earth cores of the split/con, if memory serves its the same CSA as the neutral. But clearly its a separate neutral and earth so I don't see any issue with that

@flameport , I do see your point of view that its silly that who owns it/where the meter is makes a difference, though thinking about it on the drive home, some points that I thought are important.

Firstly, Obviously with a TN-C feeder, you need to be careful with the equipotential zone, clearly the MET has to be at the far end where it becomes separate, with the area it feeds considered its own equipotential zone, with the similar set ups nearby also their own equipotential zones. I think if the DNO supply is presented in the flats themselves then this is automatic thinking. However if the DNO supply is presented in the meter room, and submains are run out to each flat then the thinking often becomes to make the whole building one equipotential zone (as one would if it were a hotel with only one meter, etc) which is all well and good when its all separate neutral and earth to the individual flats, but combine them and it doesn't work as the volt drop on the PEN conductors will put a voltage between earth bar in local DB and shared pipework. And of course, it may be that if the building was considered as one big equipotentail zone then it might need no bonds at all as the U/G pipework is plastic comming in, however if you have to treat each unit as separate then it might well be because you'll have metal services in communial areas running between units able to introduce a potential. Of course the meter position doesn't affect this, but it does affect how people tend to treat the situation.

Its half past 9 on a sunday, so I hope that makes as much sense in text as it does in my head!

Secondly, and this is a much shorter point, not only does a combined neutral and earth not comply with BS7671, but it is also not in accoradance with ESQCR if on the customers side, now as ESQCR is statutory, to have a combined earth and nuetral on the customer side is actually illegal, now providing you are happy yourself and its just sematics and of course it would be fine if the meter were just someplace else... how happy are you saying an installation is "satisfactory" when you know it does not meet statutory requirements and do you think you could justify doing that if you were called on to do so?

 

[SUNRAY]

Oh I'd be very worried if it was combined neutral and earth coming upto each flat.

It's actually tricky trying to work out what the EPZs are.
In the riser are 6 water pipes and 6 gas pipes, TV distro, all bonded to the earth bar plus the metal work in the riser and metal staircase, and more I haven't identified.
Within the flat there is no apparent equipotential bonding from the CU MET, however it would be well within a metre of the bonds in the riser. Therefore the stairs and landing area appears to be an EPZ but the flat doesn't.
I assume the second floor is the same with the remaining 4 water & gas pipes and I can see the stair bond at that level. I also assume the other 6 water & gas pipes rise elsewhere in the building but all 12 power feeds are together, neatly bolted in piles of 4 on the tray. In fact the whole installation apart from the later TV and phone alterations is very neat with all the pipe work painted silver/grey and the cut bolts/studs finished with coldgalv etc

 

[Adam_151]

I think I may have muddied the water, sorry, as long as all the submains are separate neutral and earth, then its really no different to a large commericial building and if bonded at origin (riser?) then anything above this is really just a suppliementary bond that the designer choose to have, its only if you have 'different' earths being presented off the end of CNE cables within the building (whoever owned) that it doesnt really work anymore. The metal staircase being bonded souns like the 15th edition era bonding overkill that is from time to time seen and may add hazards that would not be there otherwise (I.e. if someone is going upstairs holding tonto the rail and reaches out to lightswitch, but somone has smashed it, they'd be much better if the rail they are holding was not bonded!)

 

[SUNRAY]

I don't thinK you have muddied anything, without all of the details, I expect people to make assumptions (as I do when incomplete info is put on here).
Calling it concentric was the first mistake in my OP, sadly I don't have access to the EICR right now but I belieive it's been referred to as concentric (and not split con) and I've fallen into the trap of working straight off the EICR error.

 

[SUNRAY]

My friend has contacted the freeholder who confirms it is insulated concentric and is their responsibility. They have emailed their EICR from December 2019 to that effect. Also stating the lease holders responsibility starts at the isolator within the services cupboard.

Slight confusion there, there are 2 isolators in the riser but this one the isolator is in the flat.

AFAIC thats the end of it but now there is conflict between different EICR's.