EICR - main earth and neutral

The BNO network is the responsibility of the landlord or owner of the building unless they have appointed a contractor to operate the network with all the responsibilities that entails. BNO network has to comply with BS 7671 which is why split concentric cables are used as concentric cables with a combined neutral and earth cannot be used. There are a lot of legacy installations out there that the DNOs used to own and operate. At one time the DNOs would not allow access to the Ryfield boards on pain of prosecution now if you call them and mention Ryfield boards the response is nothing to do with us! I have a big bunch of Ryfield keys none of which fit the lock I am trying to open. I have only one of the 4 Ryfield master keys.

BNO network has to comply with BS 7671 which is why split concentric cables are used as concentric cables with a combined neutral and earth cannot be used.

Why can't a CNE be used in a BS 7671 installation? BS 7671 doesn't seem to prohibit it - indeed section 543.4 seems to specifically list the requirements for CNE conductors. Since the demise of the old Electricity Supply regs I'm not aware of any need to obtain authorization from anyone any more. The ESQCR prohibits CNEs in consumer's installations - but then a building network isn't a consumer's installation.


Granted CNEs can cause all sorts of issues you'd ideally not want within a building these days, so I doubt that anyone would want to use them for a new install - but if you're producing an EICR for an exiting CNE BN against BS 7671 the difference could be quite significant.


   - Andy.

A CNE can be used in an installation (with certain exceptions), unless prohibited by ESQCR. For installations that take an LV supply from the DNO, combined neutral and earth is usually prohibited by ESQCR downstream of the distributor's equipment - see Regulation 8(4). This is also why, even in installations with private transformers and PNB type arrangement, effectively the only bits of TN-C are effectively the transformers / generators themselves.

DNO’S do have a habit of chopping and changing. Seven flats I did in Windsor had a ducts put in and then the DNO installed split concentric cables from a Ryfield. They wanted the smart meters inside the flats. I personally don’t like to see split concentric on the customers side it’s a DNO cable at best.

I came up with the total number of neutral conductors being nineteen by doing an internet search for concentric cable, finding an image and counting them.

https://www.elandcables.com/cables/concentric-and-split-concentric-cables


However there are a couple of fillers between the neutrals and earth conductors, not as insulators just to fill the gaps, this does mean that it’s possible that carpenter could possibly fire a finish nail into the cable without touching a neutral or earth conductor, it becomes a game of Russian Roulette.

But split con is perfectly OK consumer side , in a route that does not need an SWA-like armour, like over the surface or in metal trunk -  and not being steel a damn sight easier to deal with than SWA in terms of bend radii, general flexibility and glanding.

A network operator (and the law is not clear if a BNO is included in that, but let us assume they are not) is allowed to consider neutral and earth to be at the same potential, the consumer is not. So for a DNO, split con has a surrounding earthed armour, while the other side of the meter it does not.

The situation is clearer with earthed concentric - all cores are bare, rather than the insulated neutral ones, so then it is clearer it is non ECSQR complaint consumer side, because of the PEN. That is not a BS7671 issue though so in far off lands that use BS7671 as a wiring standard but permit PEN consumer connections, I suppose earthed concentric may be used.

Mike.

All-copper split-con has been used for years in preference to SWA on the customer side because it is easier to handle and frequently preferable to large sized twin and earth. It used to be a favourite for feeding high rated electric showers in it's 10.mm guise. I used approx 19 metres  25/16mm all-copper to resite my cu at home from the front of the house to the back outhouse where the gas intake is. Switchfused down of course. It comes through the wall from the back of the meter box at the front, then goes into a length of 32mm galve and brass bushed steel conduit and rises up the wall to above ceiling level where it exits the conduit and runs through the joists all the way through the house to the consumer unit. No way could I have routed 3 core 25mm SWA through the joists, so split con was ideal. Are we now saying that this is unsafe, highly dangerous and that an imminent disasterous catastrophe is about to occur as a consequence?

I need to know before I lose my house!

Are we now saying that this is unsafe, highly dangerous and that an imminent disasterous catastrophe is about to occur as a consequence?


No.

If you have used a route that does not require earthed armour (i.e. one where T and E could be used ) then it is absolutely fine even on new works.  Even if you have not, like many common past practices, the real risk is very low.

M.