Alcomax:

Before anything else, what does the ring final serve? i.e. the real likely demand. Also, are you going to be running any other new circuits through this soon be be insulated ceiling?

Traditionally, first fix of cables has always been though centre of floor joists. Fine when no insulation, but later on any lateral runs are potentially to be covered by insulation. Similar in a way to lofts. Yes it is a problem. 16 amp or 20 amp ring reduction can help. With 4mm ring if I remember without calculating, a bit of a get out is a 25 amp OCD, though not all switchgear manufacturers do a 25 in some domestic CUs, though Hager has a full range that fits commercial and domestic. Not sure about other makes.

Thanks for the reply:


The ring final currently supplied a living room and two bedrooms. I didnt want to overcomplicate the already slightly complicated first post but can see more clarity would be useful.


The groundfloor is being reconfigured and the living room becomes a kitchen, the extension the new living room. First floor is also reconfigured from 2 bedrooms to 3 bedrooms and an ensuite.


Loads are likely to be relatively high so ring reduction below 32 Amps probably isnt going to be sufficient, certainly not for the kitchen component.

Total floor area served will be 90 square metres though I am mindful that two ring finals would probably be a better solution given the appliances that are  likely to all be in use at the same time (washing machine, dishwasher, heat pump tumble drier, coffee machine, toaster, hairdryer etc). Although the figures suggest I can just sneak in under the 32 Amps I would much prefer a belt and braces approach.


In the new area (extension) section I can run above the insulation clipped to joists as the joists are 225mm but to get to there I have to route along 170mm joists.


As you say the first fix is indeed through the 'centre' of floor joists.


Would a solution be to install substantial noggins between joists adjacent to the hole in joists and therefore be able to have the cable clipped and in contact with the noggins or joist throughout its path, provided I run 4mm2?


If I understand this correctly I would then apply reference method A, which for 4mm2 in T&E gives me 25 Amps per leg.

If I do this on alternate sides of the noggin this would give me 2 x 32 Amp ring finals 


Any flaws to my logic here?

Alcomax:

Before anything else, what does the ring final serve? i.e. the real likely demand. Also, are you going to be running any other new circuits through this soon be be insulated ceiling?

Traditionally, first fix of cables has always been though centre of floor joists. Fine when no insulation, but later on any lateral runs are potentially to be covered by insulation. Similar in a way to lofts. Yes it is a problem. 16 amp or 20 amp ring reduction can help. With 4mm ring if I remember without calculating, a bit of a get out is a 25 amp OCD, though not all switchgear manufacturers do a 25 in some domestic CUs, though Hager has a full range that fits commercial and domestic. Not sure about other makes.

Thanks for the reply:


The ring final currently supplied a living room and two bedrooms. I didnt want to overcomplicate the already slightly complicated first post but can see more clarity would be useful.


The groundfloor is being reconfigured and the living room becomes a kitchen, the extension the new living room. First floor is also reconfigured from 2 bedrooms to 3 bedrooms and an ensuite.


Loads are likely to be relatively high so ring reduction below 32 Amps probably isnt going to be sufficient, certainly not for the kitchen component.

Total floor area served will be 90 square metres though I am mindful that two ring finals would probably be a better solution given the appliances that are  likely to all be in use at the same time (washing machine, dishwasher, heat pump tumble drier, coffee machine, toaster, hairdryer etc). Although the figures suggest I can just sneak in under the 32 Amps I would much prefer a belt and braces approach.


In the new area (extension) section I can run above the insulation clipped to joists as the joists are 225mm but to get to there I have to route along 170mm joists.


As you say the first fix is indeed through the 'centre' of floor joists.


Would a solution be to install substantial noggins between joists adjacent to the hole in joists and therefore be able to have the cable clipped and in contact with the noggins or joist throughout its path, provided I run 4mm2?


If I understand this correctly I would then apply reference method A, which for 4mm2 in T&E gives me 25 Amps per leg.

If I do this on alternate sides of the noggin this would give me 2 x 32 Amp ring finals 


Any flaws to my logic here?