flex size connecting multiple ovens

One additional limitation - in UK style T and E the earth core is not insulated, and it 'only' damages the the jacket rather than carbonising the functional insulation in contact with  a live core when it gets hot.

Now, as shown above, the reduced CPC is fine for a B40 MCB anyway except for the sort of fault current you won't get unless you live next to the substation and the cooker cable is very short, even if you are at near the full 6KA PSSC at the MCB end- , but to be always OK, the use of a reduced size cpc relative to live is based on the CPC not  being pre-heated by the load current in the way the L and N might be, so the initial temperature for PVC is never starting at the full 70c (though in well lagged environments it will only be 5 to 10 degrees below the current carrying cores ), and the plastic around it is not considered to be so valuable as proper insulation.

There is a reason that in those countries that have now decided to insulate their CPCs in their T and E like cables, Ireland and New Zealand come to mind as having abandoned bare earths since 2000, they have at the same time  included a requirement for the copper cross-section of the CPC to be now equal to that of the live.


And in any case a larger CPC is good in TNx systems also because it helps reduce the touch voltage that occurs during the short time that ADS is operating.

Mike, I don't really get your point about bare-E T&E. Surely in UK-style T&E, the bare E is (on the long axis anyway) touching or almost touching both the L and N's insulation. So there is only a single thickness of insulation between L+E that needs to gets charred before a L-E short circuit develops. Whereas the Irish/NZ full fat T&E will have at least two thicknesses of insulation between L+E. So they should in fact be more robust against transient overheating than the UK and thus less needful than the UK of having a full-size cpc ???

I do take your point that while the L and N  cores will be trying to melt out of their insulation,  it is quite possible  the CPC is trying to melt into one or other of them (which really would matter) rather than simply out of the jacket (which probably would not).

The more thickly insulated CPC is not so well cooled, so may reach a higher temperature, but the point I was making was that there is no insulation we care about on the CPC in twin and earth - the outer jacket although it is of course insulating, is not considered an insulation, but a mechanical protection, in the form of  a sheath equivalent to double insulation  ( the sort of clumsy definition  you sometimes get when two committees develop standards independently and do not cross  reference.)

If you do care about this then the the advice that the  reduced CPC twin and earth is suitable for all possible PSSC values cannot be supported.