90m for a downstairs ring?!

[Donkmeister]

I'm doing my cable calcs to rewire my house (will one day get to doing the actual wiring!!!) and I've worked out the ring for my downstairs sockets will be 90m... This sounds excessive to me, but when I measure and remeasure it comes out the same. I'm taking into account the proper places where I can drill/notch joists, so sometimes the routes are a little longer than would be electrically ideal.

The OSG reckons that 2.5mm T&E, clipped direct, on a 32A mcb, RCD protected, with TN-S supply, allows for a 106m ring so I should be OK, it just feels like cutting it a little close when most of my other circuits are coming out with a massive margin to spare!

3-bed house, ring covers living room, hallway, dining room.
Concrete floors, so cable drops from ceiling (approx 2.5m ceiling height so each drop adds between 4m and 5m depending on where it is)

2 drops in hallway, 4 drops in dining room and 5 in living room (so at least 44m of cable is purely for the drops).

Total floor area served about 60m^2

 

[electronicsuk]

If that's the length of the circuit and you've been a little generous with your measurements, there shouldn't be too much to worry about. However, you aren't forced to use ring finals, nor are you forced to use the same circuit for three rooms if you feel that serving fewer rooms would result in a shorter circuit.

 

[Donkmeister]

If that's the length of the circuit and you've been a little generous with your measurements, there shouldn't be too much to worry about. However, you aren't forced to use ring finals, nor are you forced to use the same circuit for three rooms if you feel that serving fewer rooms would result in a shorter circuit.

Probably not a bad idea to put the living room on a separate ring... does mean a total of 5 rings in the house though

 

[electronicsuk]

Probably not such a bad thing!

 

[Chri5]

Why not go radials on 4mm or 20 amp / 2.5mm ??