hello and welcome to the second in this series of videos where we're looking at twin and CPC
cables in this video we're going to be particularly focusing on the typical sizes
of twin and CPC cables are available and we're also going to consider how the CPC size relates to
the main conductor size so first up on our list of conductor sizes is the smallest size available for
twin and CPC and that is one millimeter squared so what that means is that the cross-sectional area
of the line and the neutral conductors are one millimeter squared in their cross-sectional area
now this is the only twin and CPC cable where the CPC is actually the exact same size
as the line and neutral conductors so the line in neutral are one millimeter squared and the CPC is
also one millimeter squared now you'll start to notice as we go up the cable sizes that the CPC
will start being a different size to the line in neutral so we'll have a look at our next size up
our next size up is 1.5 millimeter squared so again that's referring to the cross-sectional
area of the conductor is 1.5 millimeter squared if you're ever unsure about your conductor size
most cables manufactured now will actually have the size of the cable printed on there
embossed into the outer sheath so you can actually get a bit of a clue there as to what size it is
so here we've got 1.5 mil for the line and the neutral and then the CPC is one millimeter so
you can see there that is half a millimeter squared smaller than the line and the neutral
now the main reason for that is that as we said in a previous video this CPC should never
have any electricity running through it that's the ideal it should never have any electricity
running through there at all however if a fault occurs this CPC may carry some current but it
will only carry current for a very short period of time which means that it's not going to get
a long time to get as hot as the line or the neutral may therefore this conductor
can be smaller than the line in neutral now there's ways of proving that in the
regulations but we'll cover that in a slightly more advanced video our next conductor size up
is 2.5 mil so this is a very common size that we use for socket circuits and this is
2.5 millimeter squared for the line in neutral and the CPC is 1.5 mil so again you can see that
that is one millimeter squared smaller than the line and neutral conductors so typically used
for socket outlets and this next size up is four millimeter now at this point you'll notice
that the conductor type changes for the line and the neutral you see there that in the previous
cables the conductors were solid they were made from a single solid piece of copper wire
but here these conductors are actually stranded so they're made out of
seven much smaller pieces of solid wire that are then all twisted together to make one conductor
so the reason for that is that as you get past 2.5 mil in size if these were solid conductors
it would make this cable very very stiff and very difficult to bend and to install
so that's why it goes up to a stranded size so we've got four mil squared for the line and
neutral conductors and we've got 1.5 ml squared for the CPC so now we get into a position where
actually this conductor is getting quite a bit smaller than this one we're talking about
two and a half mil smaller so it's getting considerably smaller than the line in neutral
but again remember this should never conduct electricity if it ever does conduct electricity
it should only be for a very short period of time four mil cable is often used on socket circuits
where the runs are a little bit longer and there might be issues with volt drop and also it might
just be used for standalone supplies to pieces of equipment with slightly higher current ratings
than normal next on our list of conductors we've got six mil so that is six mil for the line and
the neutral conductors and now we're looking at 2.5 mil for the CPC so 6 mil for the line
and the neutral 2.5 mil for the CPC so again this conductor is smaller still than these two
this size of conductor in a domestic installation would typically be used for a cooker
can't state categorically that it will suit every single cooker installation but it is typically
used for that we then move on to some much larger cable sizes so now we've jumped from six mil all
the way up to 10 mil so this is a 10 mil conductor on the line in the neutral and you'll notice as
well there's another change in that the CPC has now become stranded as well as the line and the
neutral conductors so we've got a 10 mil liner neutral conductor and the CPC is a 4 mil conductor
so again this is this is quite a lot smaller than these two but that's no there's no issue with
safety there because it should only ever conduct electricity for the briefest of moments in fault
condition a 10 mil cable will typically be used in a domestic installation for a shower installation
again you can't guarantee that every shower will need 10 mil but that's a typical size that is used
and finally we've got our largest size of twin CPC this is 16 mil this is quite a big cable
it's not off it's not all that common that this will be used in a domestic installation but we've
got a 16 mil line of neutral conductors and we've got a six mil CPC so again we've got to the point
now where this is really getting quite small this is less than half the size of these two but again
there's no safety implications there because lots of calculations have been done to prove that this
conductor is quite safe to be this size a 16 mil cable might be used on some very large powered
showers uh it may also be used as a sub main cable for getting from one consumer unit to another
and it's it's fairly rare that this gets used in domestic installations you might
not come across this that that often but it is available should you ever require it
so Gary we've covered the typical cable sizes that we can expect to be working with when we're
working between CPC how's this going to fit in with the learner experience what are they
going to know from this how are they going to benefit early low level stuff they've got to
be identified the right size cable for the right type of circuit so we'd be expecting our learners
to know that one and 1.5 millimeter square k would be used for lighting circuits and then we've got
to distinguish the cable sizes for an A1 A2 and A3 arrangement of the socket outlets as we move
towards a level three course we'll be looking at the design elements and sizing cables so a
little bit more difficult the longer you're with us yeah so at that point we'll start to look at
not necessarily typical circuits but circuits that you design from scratch and of course then
we realize that there's a lot more freedom about selecting conductor sizes and making sure you get
it right for the load so that's that's going to be a lot of fun and very interesting to deliver
and uh the learners will enjoy that while they're here i think it's that time
shall we we'll try we hope this video has been some help