Connecting Multiple Bemco/Ryefield Boards

What is the ASC from the DNO for this supply?


Regards


BOD

300kVA. we are having a 500kva sub built on site.

What DNO area are you in?


Different DNOs have different approaches - UKPN for example will want you to form a 'BNO', in which case Lucy MSDBs would be a good solution.


Simon

Hi Simon


its SP Energy Networks on this one.

80+ flats?


Regards


BOD

I agree. Apart from any other considerations, it is common practice to supply a Ryefield board with a 315 amp circuit from the substation. If the largest readily available Ryefield board is fully populated with 60 amp or larger fuses, then the total load may approach 315 amps. Connecting two such boards to the same 315 amp circuit might lead to operation of the substation fuses under peak load.

I just had a quick look at SPENs earthing policy, and like most of the other DNOs they don’t seem to allow multiple services into ‘multiple occupied buildings’. 


This is because of the risk of diverted currents running though the structural steel work with multiple PME services.


So multiple services direct from the fuse ways in the DNO sub is probably not an option.


Usually I would recommend the DNO cut out to terminate in communal area, with PME terminal provided. Then cable that to Lucy MSDBs, all SNE earthing. 


Your load is a bit high though, surely you have multiple cores at that load?


Simon

https://www.spenergynetworks.co.uk/userfiles/file/EART-01-002.pdf

The largest common Ryefield, I think, is something like 24 fuses (8 per phase) , if you need 3 of these, then that is 72 properties, is that about right ?


If it is like that or bigger  you may well find it warrants an upgrade to the transformer or even its own new substation, or would round here, where we seem to have about 50-70 properties  per phase on a half MVA transformer as the largest arrangement in common use and not that that much slack. I do realize there are bigger things in cities, and it will depend where you are.

Equally, there are plenty of set-ups with less, I've recently stuck my head in a cupboard where 21 flats and a common areas supply all shared a rather ropey 3 phase 100A header, in a Victorian building with no gas. Luckily the diversity to justify that  is not mine to worry about, and the incomer did not look particularly cooked, though the lights in the flats do seem to dim and bright a lot, presumably with neighbour's water heaters and so on.

And if you can’t keep the load to under 400 Amps, then give SPEN your cables to terminate on their dedicated fuse way (fused at 630 Amps), terminate the other end in the first Lucy MSDB, they ‘daisy chain’ the other two from there.


Lucy MSDB:

https://www.lucyelectric.com/product/msdb-vertical-busbar/


Not sure how SPEN meter this, some DNOs now have the CTs in the dedicated fuse way within the DNO sub, but some will need a CT chamber.


Although if all the services within your building have full settlement metering, then no metering is required on the incoming bulk supply.


This forms a BNO network, who ever manages the building needs to take that on and its responsibilities.


if an IDNO adopts the sub, usually they will adopt the BNO network too, making things simpler.


Simon