I am.Yep, that too.
Are you asking whether a 1.5mm² CPC is always adequate for a circuit whose live conductors were 2.5mm² (or 4mm²)?
We do assume that.If so, then that's an interesting question, which I doubt that any of us ever really consider - if the CSA of the live conductors is adequate for the design load, then we simply 'assume' that the CPC that comes in T+E of appropriate size will always be adequate.
Quite.I don't know whether it ever happens in practice but I suppose that, in theory, the CPC of T+E is not always (adiabatically) adequate. The required CSA depends upon I²t and, as far as I am aware, I²t continues to rise ('indefinitely') as PFC rises. Since there is 'almost no limit' to how high PFC can be (one sometimes sees figures of 'thousands of amps mentioned), I presume that it is 'not impossible' (with a very short circuit in an installation next to a substation) that it could be so high that the CSA of the standard CPC was inadequate. However, I cannot recall having even seen/heard anyone even considering that possibility.
Not sure I follow that.That's easy, but you're perhaps asking the question the wrong way around. The point is that, in adiabatic terms, the live conductors are 'oversized' - but, for those live conductors, there is also the consideration of the ('continuous') current-carrying-capacity (the antithesis of 'adiabatic'). In other words, considering 2.5/1.5mm² T+E, 1.5mm² would be adiabatically adequate for the live conductors, but the cable would then only have the CCC of 1.5mm² cable, not that of "2.5mm²" cable.
Yes.You mean flex?
Yes. As above, they must always be larger than actually necessary.If so, that's another 'good question' - since theory would indicate that the same 'conventional relationship' between CPC and live conductor CSAs would be just the same as in T+E.
Indeed - but, as I said, at least in theory (I don't know about 'in practice') the CPC of T+E is not always going to be adequate.I am. ... We do assume that. .... IF it is adequate then that must mean that the CPCs in other cables [and if using the same size singles CPC (as live conductors) because we do (not sure if that is just habit or normal practice to avoid calculation)] is always over-sized.
"CCC" and the maximum current a conductor can safely cope with under adiabatic conditions are two very different things. "CCC" (Iz - or, in fact, at least 1.13 x 1z) is the maximum current that a a cable is deemed to be able to carry safely for a continuous/indefinite period of time - and will inevitably be less than the current that it is deemed to be able to 'safely' carry under adiabatic conditions (i.e. conventionally for no more than 5 seconds - and for no more than 0.1 seconds if one goes by 434.5.2).Not sure I follow that. 1
That might sometimes be a small consideration - but with a short final circuit in a TN-C-S installation there would be very little difference between the two.Plus, the PSCC would be higher than the PEFC.
Indeed. If the CSA of CPCs in T+E is deemed to be 'adequate', then those in all flexible cables >1.0mm² must be appreciably 'more than adequate' (aka 'over-sized').Yes. As above, they must always be larger than actually necessary.
I have a drum of flex here, for a long time, which does indeed have a smaller CPC.You mean flex? If so, that's another 'good question' - since theory would indicate that the same 'conventional relationship' between CPC and live conductor CSAs would be just the same as in T+E.
Kind Regards, John
Interesting. In some senses 'consistent' (with T+E), but I must say that I have never seen, nor even heard of, such an animal.I have a drum of flex here, for a long time, which does indeed have a smaller CPC.
I purchased since 1974 as I remember the car I had when I got them. Originally a dozen reels of which I fitted plug & socket (XLR) on one, the rest have been used for installation work. I have every expectation it is harmonised but over 40 years I hay be wrong.Interesting. In some senses 'consistent' (with T+E), but I must say that I have never seen, nor even heard of, such an animal.
Does the cable in question have harmonised colours?
Kind Regards, John
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