Main Incoming Cable

andyp69 · Feb 13, 2013

Hi Guys

My first post here....so hello all.

I have very recently looked at the electrics in a flat with respect to doing at PIR for the owner before he lets it out.

I did not have access to the meter cupboard which is on a differnt floor to the flat. (I have requested access but so far have not been able to get it).
The main incoming cable from the meter into the CU in the flat is something i've never seen before.
The brown live cable is a normal single cable as i'd expect to see. The blue neutral seems to be a lot of individual small csa cables all connected into the main neutral on the isolator switch. The total csa in relation to the single live looks to be ok. Live is 16mm. The individual neutrals look very similar in total to 16mm.
Everything else in the CU looks ok. The External Earth loop reading on the mains is good. (0.26ohms).

Is this sort of main incoming neutral acceptable or should it be a single cable.

There are quite a few other issues with the install which are internal to the flat. With the main supply being external - if the supply cable is an issue then i guess it may be down to the owner of the buiding.
Not really sure what to put on the PIR thou.

Any assistance would be greatly appreciated.

Engineer54 · Feb 13, 2013

That sounds like a concentric cable, usually favoured by the DNO's!! I take it this is a PME installation, otherwise this would have been a ''split'' concentric cable where the earth strands would be of the same number but bare, and used for TN-S supplies!!

Having said that, if this is a sub-main supply, i would have thought this should be a split concentric cable, the N-E PME connection should only apply to the DNO's incoming supply, not at every flat in the building.
You really need to get access to that main in-take room to check the distribution arrangement before making a judgement!!

somersetsparks · Feb 13, 2013

As engineer says, SHOULD be split-concentric, however it should also be terminated into a cut-out with red link (solid link) if it was the DNO's cable,
Maybe the builders took responsibility for the flats submains and used split-con?
Does it have 4 g/y sleeved bare 2.5ish strands as the main earth?

andyp69 · Feb 25, 2013

Hi. Appologies for not getting back on here. I have been in a car acciednt and off the radar for a few days.
The g/y sleeved bare cables are used as the main earth.
Due to my accident i have not been back to this job to inspect anything else. Hopefully i'll be back to it later this week.
The mains incoming cable has been changed since the 2005 colour changes as they are brown and blue. All of the cables in the consumer unit are red / black.
I will trry to get photos when i go back.
I am assuming by the replies that although not typically used as a mains incom,ing cable, this is accaptable. My initial feeling was that if one or more of the single stranded Neutral conductors were not connected properly it would lose CSA and therefore become undersized.

I will give better updates as soon as i can.

Engineer54 · Feb 25, 2013

OK, so this is a split concentric cable that's supplying this flat. So all well and good, providing the conductors are all solidly connected to it's termination points!!