Running another socket from a junction box.

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We still don't know if the CPD at the house end is 6amp or 63A.
We don't, but if there is a downstream (and, one imagines, very close) FCU, the rating of the OPD at the house is irrelevant, isn't it? Indeed, you seem to have taken that concept on board, since even you have suggested the use of 2.5mm² cable, which would be unacceptable if one were relying on protection from an upstream 63A (or even 32A) OPD.
In any case he has already bought himself a reel of 0.75mm² cable http://www.selcobw.com/0-75mm-3-core-round-flex-50m ... Would you be happy for that to be installed with a very large CPD protecting it?
That's obviously a totally different issue from the suggestion that 2.5mm² is needed (whereas I suggested that 1.5mm² would be adequate). For a start, although 0.75mm² flex would technically be OK if there were a downstream 3A or 5A fuse in an FCU, I would certainly want the cable to be adequate should that fuse ever be changed to a 13A one - and 0.75mm² flex would not satisfy that. Also, I'm not sure whether a connection from a 'power' circuit to an FCU supplying lighting counts as being part of a 'power' or 'lighting' circuit - if the former, the minimum permitted cable size would be 1.5mm². ... so, no, I would not regard it as acceptable to use 0.75mm² flex, no matter what the size of the OPD (unless it were 6A, which seems very unlikely!).

Kind Regards, John
 
I recently wrote:
... Also, I'm not sure whether a connection from a 'power' circuit to an FCU supplying lighting counts as being part of a 'power' or 'lighting' circuit - if the former, the minimum permitted cable size would be 1.5mm². ... so, no, I would not regard it as acceptable to use 0.75mm² flex, no matter what the size of the OPD (unless it were 6A, which seems very unlikely!).
It's just occured to me that even if the bit of cable were regarded as part of a 'lighting circuit', it would still be required to have a minimum size of 1mm² - so 0.75mm² would be a definite no-no, regardless of everything else, even if (very unlikley) the upstream OPD were 6A..

Kind Regards, John
 
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For a start, although 0.75mm² flex would technically be OK if there were a downstream 3A or 5A fuse in an FCU, I would certainly want the cable to be adequate should that fuse ever be changed to a 13A one - and 0.75mm² flex would not satisfy that.
Unless it can't be overloaded.

Also, I'm not sure whether a connection from a 'power' circuit to an FCU supplying lighting counts as being part of a 'power' or 'lighting' circuit
It's a lighting circuit only if you have lights that don't use power.


It's just occured to me that even if the bit of cable were regarded as part of a 'lighting circuit', it would still be required to have a minimum size of 1mm² - so 0.75mm² would be a definite no-no.
Unless for a specific appliance. :)
 
For a start, although 0.75mm² flex would technically be OK if there were a downstream 3A or 5A fuse in an FCU, I would certainly want the cable to be adequate should that fuse ever be changed to a 13A one - and 0.75mm² flex would not satisfy that.
Unless it can't be overloaded.
If the fuse were changed to a 13A one and any load >6A were connected, then it would be overloaded. I know that there is a limit to the extent to which it is sensible to cater for 'what might happen in the future', but changing an FCU fuse and its load are, IMO, probably possibilities one should cater for.
It's just occured to me that even if the bit of cable were regarded as part of a 'lighting circuit', it would still be required to have a minimum size of 1mm² - so 0.75mm² would be a definite no-no.
Unless for a specific appliance. :)
As above, I personally don't think it's particularly safe to assume that an FCU will never be used for a different load. In any event, I think the bit of the regs you'[re thinking about is probably actually referring to flex ('leads') connected to appliances, not 'fixed wiring' (part of 'a circuit').

Kind Regards, John
 
For a start, although 0.75mm² flex would technically be OK if there were a downstream 3A or 5A fuse in an FCU, I would certainly want the cable to be adequate should that fuse ever be changed to a 13A one - and 0.75mm² flex would not satisfy that.
Unless it can't be overloaded.
If the fuse were changed to a 13A one and any load >6A were connected, then it would be overloaded.
If the designer had used such cable and a 3A fuse then it, presumably would not be overloaded.

I know that there is a limit to the extent to which it is sensible to cater for 'what might happen in the future', but changing an FCU fuse and its load are, IMO, probably possibilities one should cater for.
I would disagree that it has to be considered.
Are you saying ALL shower circuits must be 10mm²?

It's just occured to me that even if the bit of cable were regarded as part of a 'lighting circuit', it would still be required to have a minimum size of 1mm² - so 0.75mm² would be a definite no-no.
Unless for a specific appliance. :)
As above, I personally don't think it's particularly safe to assume that an FCU will never be used for a different load. In any event, I think the bit of the regs you'[re thinking about is probably actually referring to flex ('leads') connected to appliances, not 'fixed wiring' (part of 'a circuit').
I am, as I am sure you were, referring to the brilliant Table 52.3 where it does not state "connected to appliances, not 'fixed wiring'".
On the contrary, it does state "For any other application" (i.e. other than "As specified in the product standard" (for a specific appliance)).
It also mentions signalling and controls circuits of 0.1mm², which may very well be fixed wiring.
 
If the designer had used such cable and a 3A fuse then it, presumably would not be overloaded.
Presumably not ... until some unskilled person came along and changed the fuse (and maybe the load)
I know that there is a limit to the extent to which it is sensible to cater for 'what might happen in the future', but changing an FCU fuse and its load are, IMO, probably possibilities one should cater for.
I would disagree that it has to be considered. Are you saying ALL shower circuits must be 10mm²?
As I implied, there has to be a judgment. IMO, it's far more likely that an 'unskilled person' will change the fuse (and maybe the load) in an FCU than they will change a shower for a higher powered one. Some, presumably including you, will disagree with that judgement.
I am, as I am sure you were, referring to the brilliant Table 52.3 where it does not state "connected to appliances, not 'fixed wiring'". On the contrary, it does state "For any other application" (i.e. other than "As specified in the product standard" (for a specific appliance)). It also mentions signalling and controls circuits of 0.1mm², which may very well be fixed wiring.
I was, indeed, referring to that Table, which is diabolical for several reasons. We both know what it says, and does not say, but I was making an attempt to guess at the intended spirit of it. It really is daft, since "Any other application" could include 'power circuits' and 'lighting circuits' - in which case 0.75mm² flex could (subject to OPD etc.) presumably be used for such circuits - contrary to what the first part of the Table says (which doesn't say whether it is talking about flexible or 'non-flexible' cables!)!

Whatever, I still would personally not use 0.75mm² flex to feed any FCU, regardless of how one wishes to interpret (or try to interpret) that Table.

Kind Regards, John
 

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