Ive been pulling up floorboards in my c1950s house and noticed cables are 2.5mm, although the cables into 32A fuses in MCB are 4-6mm. I think its a radial circuit as theres only one cable into each fuse?. The MCB has 2 x 16A fuses which im unsure what they are for, although shed has lights and power so they may be for that? There are 3 x 32 A fuses. One is for most of the sockets upstairs and downstairs. One is for cooker, an adjacent double socket, a single socket in bedroom above, a fused switch for outside socket and a dishwasher (which presumable is plugged into another socket beneath the kitchen units). Im not sure what third 32 A fuse is for. Does this sound okay, as alot of the cables supplying the sockets upstairs seem to be 2.5mm and from reading other posts they should be 4mm?
4mm to 2.5mm on radial
- Thread starter Richely
- Start date
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Ring circuits have dispensation to use 2.5mm on 30 or 32 A breakers
M16A could be for immersion heater in tank
M16A could be for immersion heater in tank
It's not idea having junction boxes under flooring like that. Ideally the Circuits on the 32A should be Ring Final circuits or All 4mm cable as Radials.
If the 32MCBs supply Radials on 4mm and 2.5 mm has been used along the circuit then the MCBS should be downsized to 20A. There's lots of "If" "buts" & "maybes" without more investigation it's hard to give good advice. The installaion is at least proptected by an RCD - the whole of it which is safe but not ideal as any fault that causes the RCD to Trip will cut power to the whole installation.
If the 32MCBs supply Radials on 4mm and 2.5 mm has been used along the circuit then the MCBS should be downsized to 20A. There's lots of "If" "buts" & "maybes" without more investigation it's hard to give good advice. The installaion is at least proptected by an RCD - the whole of it which is safe but not ideal as any fault that causes the RCD to Trip will cut power to the whole installation.
Thanks for the replies, good to know the rcd at least makes it a bit safer...just out of interest, why are the junction boxes not ideal?
Anyway, i had planned to take the cable out of the wall (back wall in pic) and run it into a new socket (bottom right of wall in pic) which i think was its origional location before the room was made into a bathroom (theres an existing hole chased out in wall). I also thought to run cable from the existing junction box to make a new socket on another wall in the room...does this seem okay and what cable size would you use?
Anyway, i had planned to take the cable out of the wall (back wall in pic) and run it into a new socket (bottom right of wall in pic) which i think was its origional location before the room was made into a bathroom (theres an existing hole chased out in wall). I also thought to run cable from the existing junction box to make a new socket on another wall in the room...does this seem okay and what cable size would you use?
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Any joint between electrical conductors is a potential point of failure (e.g. can become 'lose', overheat and cause fires), so the fewer joints there are, anywhere, in an electrical installation, the better - and particularly theoretically 'non-deal' when concealed under floor boards etc. (in which case the Fire Brigade could well be the first people to become aware of any problem).
Having said that, there are undoubtedly countless millions of JBs (many 'concealed') in service, many of which have been in service for decades, without any problems.
Kind Regards, John
You are allowed to run a spur in 2.5mm
No.
Ring circuits are allowed to be 32A
Ring circuits are allowed to be 32A
The fact that there are 2 junction boxes under the floor would hint at a ring
You should check at the fuse box to be sure.
Turn power off
Remove 2 red wires from Mcb
And check they have continuity
Ie a ring. If they do 32 is ok.
Refit red wires.
Also check black wires if you can understand which ones they are
You should check at the fuse box to be sure.
Turn power off
Remove 2 red wires from Mcb
And check they have continuity
Ie a ring. If they do 32 is ok.
Refit red wires.
Also check black wires if you can understand which ones they are
Suggest you find out what every Mcb does first.
Turn off each Mcb separately. And see what doesn’t work.
Mark on the cover what they do.
Turn off each Mcb separately. And see what doesn’t work.
Mark on the cover what they do.
So on MCB; from L to R
6A - all lights inside and outside
16A - shed sockets and lights
16A - doesnt seem to turn anything off
32A - most sockets downstairs and upstairs
32A - again doesnt seem to turn anything off
32A - cooker, an adjacent double socket, a single socket in bedroom above, a fused switch for outside socket and dishwasher (which presumable is plugged into another socket beneath the kitchen units)
Ive attached pic of unit with box removed...i havent tested any cables yet, what do you think?
6A - all lights inside and outside
16A - shed sockets and lights
16A - doesnt seem to turn anything off
32A - most sockets downstairs and upstairs
32A - again doesnt seem to turn anything off
32A - cooker, an adjacent double socket, a single socket in bedroom above, a fused switch for outside socket and dishwasher (which presumable is plugged into another socket beneath the kitchen units)
Ive attached pic of unit with box removed...i havent tested any cables yet, what do you think?
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