hello welcome to this YouTube tutorial video in this video we're going to be talking
about a particular type of cable you'll often see it in domestic installations
commercial installations and perhaps an office areas of industrial installations and that cable
is what you will commonly hear referred to by sparks as twin and earth but of course that is the
uh the vernacular term for it if you like what we're going to be referring to it here
by its proper name now its proper name as we refer to it in the college i'm sure it will be
lots of sparks watching this will be cracking up when i say this we refer to this as pvc pvc
thermoplastic twin and cpc cable now that's quite a mouthful and when you go into the wholesalers
there's no way you're going to be asking for that when you go into a wholesalers you ask for twin
and earth and you know what you're going to get but let's break down that big long name that we
just spoke about by having a little look at the structure of this cable so let's have a
look at the structure of this cable now we just gave that big long name to this cable
which was pvc pvc thermo plastic twin and cpc cable so let's break that down because that big
long name actually helps us to understand a lot about the structure of the cable so we've got
first of all pvc now that refers to this part of the cable this part of the cable is what we call
the sheath now it's important to understand that this sheath is offering mechanical protection this
layer does not act as an insulating layer except incidentally its primary function is there to act
as mechanical protection and it's made out of pvc which we know stands for polyvinyl chloride
so that's our the first part of our name pvc now you see from the structure of this cable you can
see it's flat in its shape in the way that it's laid out the reason for that is that this cable
is actually designed to be buried inside walls it's designed to go underneath plasterboard or
to be put on a wall have a layer of capping over it and then have a plaster put over the
top of it and really this layer all it does is provide mechanical protection against the
plasterers trowel you can see pvc is a very soft material i can almost scratch
it and dent it with my nail there so it's not going to withstand someone trying to
drill it or put a screw through it or something like that it's just there to offer protection
against a plasterer's trowel so you would never install this in an area where there's a high risk
of mechanical damage so that's the first part of our name pvc we then have a second pvc and that
refers to this layer here this is referring to the actual insulation that covers the copper conductor
of this cable so that's what we mean by pvc pvc so this layer here and this layer here
are covered in a layer of pvc insulation and that is there to insulate the copper conductor to stop
the electricity from jumping out and leaking to places that we don't want it to go to you'll
notice the center core has no insulation over it the reason for that is that this cable is never
in in good circumstances should never carry any current and therefore doesn't require insulation
and if it ever does carry current we'll cover in a later video you'll see that actually
it only carries current for a very short while but when this is terminated we don't like to
leave just that bare copper sticking out there so it's common practice to use some green and yellow
sleeving now earth's leaving it's referred to cut to the right length and that just pops over at the
end of that conductor and covers it up apart from the end part where you would terminate it
so we've got pvc pvc and then the next part of the name is thermoplastic thermoplastic so what does
that refer to well a thermoplastic is a group of plastic type materials of which pvc is one
and that family of materials behave in a very specific way thermoplastics
retain their malleability when they get warm when they heat up and they can be remolded
there is another family of plastics called thermosetting and we do use that on a particular
type of cable particularly on armored cable but we'll we'll cover that in another video
so this layer of insulation this pvc thermoplastic layer has a very specific operating temperature
which is 70 degrees c if you open up your regs book or your on-site guide you'll see 70 degrees
c splashed all over the book and that's very important for the following reason we know that
when electricity flows through a conductor one of the three effects that it has is that it starts to
heat up the conductor the conductor will start to get hot therefore this layer of insulation
has to be able to deal with that heat without breaking down so that means that this layer of
conduct layer of insulation which is 70 degrees c thermoplastic pvc can get up to 70 degrees c
before it will start to break down before it will start to melt and potentially break down and allow
electricity to jump to places that we don't want it to go to we then move on to the part where we
talk about this being twin and cpc now you may be looking at this cable and thinking but joe there's
there's three conductors there i can see three conductors we only actually count the insulated
conductors if you like so you can see here that we've got one insulated conductor two insulated
conductors so that's where our twin comes from and then we've got cpc which is this conductor in the
middle again you'll often hear this be referred to as earth this is not an earth cable an earth
conductor this is technically a cpc but again the the difference between those will be covered
in another video so that's where we get the name from for this cable it is pvc pvc thermoplastic
twin and cpc cable so Gary that covers the construction of this type of cable the pvc
pvc twin cpc where's this going to fit in with our studio program here at the college extensively for
the first 10 weeks of all the study programs they're going to be doing at the college
we'll be using pvc pvc thermoplastic twin and cpc cables and most of those circuits to start with
they're going to be light in circuits so we'll go through one way two way intermediate switching
using this style of cables good stuff well in that case we hope this video has been smelled