New circuit design question

[westward10]

It is a mission to get a 16mm into a single phase boards and a 70mm will be mission impossible. Just the gland for a three core would be 40mm.

 

[pc1966]

I don't expect the load at any kiosk to exceed 10A, except for the last kiosk which will be around 40A I would suspect, but again, there may be more in the future (there is a barn close to the final kiosk which will likely want lighting and sockets in eventually.

I have decided to go for an 100A switched fuse after the meter. 100A main isolator in kiosk 2 and 3. With the feed from kiosk 2 down to 3 via an 80A MCB. Then from kiosk 3 to the final kiosk via a 63A MCB. All lighting circuits on MCB and the rings on RCBOs. At the final kiosk will be a 30mA RCD which will feed a future ring and lighting,it will also

If you expect 10A max or so then why a 80A MCB???

Also you won't get very good selectivity with MCB/fuse, and none guaranteed if 100A fuse and 80A MCB!

Though to be fair you probably won't have a PFC/PSSC high enough by the end to cause problems (e.g. Hagar say 63A B MCB of the NBN commercial B-curve is selective to 4.3kA with a 100A BS88 fuse).

Really you would be much better putting in 63A switch-fuses for each kiosk and then your choice of 32A/6A RCBOs, etc. Then you get selectivity with your incoming & the DNO fuses, can safely run 16mm or 10mm from the output of the switched fuse to the kiosk, and the final circuits are selective to around 1.1kA for faults on the ring not taking out the 63A fuses (again, based on Hager guide and that by the far end I doubt you will be seeing much more than 1kA or so PFC).

 

[pc1966]

How about using a branch joint to bring off some 25mm SWA that connected to your kiosk:
https://www.cef.co.uk/catalogue/pro...-resin-joint-kit-for-cables-up-to-70mm-4-core

I think they so a MS70 that might be better here for taking off a thinner cable, but not obvious on the usual suspect's web sites:
https://www.birkett-electric.com/v3/multi-service-cable-joints/

 

[David Prosser]

So because there may be a very slim change of the main fuse blowing with a 63A fuse in the SFI, then you choose to do no selectivity whatsoever... Interesting.... Not something I would do.

A fault that is going to blow the 80A fuses is also likely to blow the 100A fuses you get no realistic discrimination . There's no point in limiting yourself further down stream by starting with 80A fuses.