19 Flats fed via Mccb/ryefield.........isolaters??

sparkybaz · Oct 10, 2023

Hi all,
I am currently in the process of quoting a job to renew the mains for 19 flats. This is the first job of this type that I have quoted so just after a bit of advice.
The flats are currently supplied via a ryefield panel in mains room which supply's a further 4 ryefield panels in risers. If I were to replace the ryefield in mains room to a new mccb panel to then supply ryefields in risers would I then have to install switch fuse isolaters after ryefield? Thanks

ipf · Oct 10, 2023

Not absolutely sure I'm following you. I would have thought the riser Ryefields are still fused panels with isolation at distributed points.

pc1966 · Oct 11, 2023

I also don't see the need for switch-fuses after the Ryefield - typically each flat will have a cut-out with a solid link for local (i.e. sparky working in anyone's flat) isolation and the design ought to be such that the Ryefield's fuse can protect cables to that point. Ideally they would have isolation switches after the billing meters but we know that is not always the case

What I am not clear about is if they have to follow 5 sec distribution circuit ADS per wiring regs that sparks follow, or if they fall under DNO regs where it is simply overload protection of the network?

As for replacing the Ryefield at the origin with a MCCB panel that is up to you. If there is any need for a non-skilled person to be able to isolate or reset then MCCB fit the bill, but otherwise fused Ryefield along with some incoming isolator switch is likely cheaper and provide better fault selectivity if you have at least a 1.6:1 ratio. E.g. With 19 flats and 4 sub-Ryefield it looks like 5 flats per board, so about two per phase. They are probably on 60A fuses (any info on per-flat demand estimate?) so if the source Ryefield is using at least 100A fuses then total selectivity is possible and probably fine for diversity of loads.

Same for those and the incomer, if the DNO incomer is at least 160A fuse per phase then you ought to have total selectivity with the first board at 100A, etc.