in this video we are going to take a look at flexible cables we are going to look at the common
number of conductors within the cable as well as their cross-sectional area we'll look at the
outer sheath colours and how they can be used to identify the voltage of the equipment being used
i'll also show you how to strip off the outer sheathing as we lead into our next video
where we look at the BS 1363 plug top let's bring the camera in and let's take a closer look
let's first of all look at the conductors themselves so this here being a three core flex
and obviously flex meaning flexibility because of this the fine strands of copper that we've got in
our conductors which is slightly different some of the other videos that were seen on the channel
this is a class 5 conductor and that's worth bearing in mind when we look at what we've
already seen on the channel so our twin and CPC or twin and earth cables have in this case a solid
copper conductor and that's class one and we used stranded cables but were solid copper stranded
when we did our conduit system and conduit wiring because again we said being solid stranded that
had greater flexibility so this is a class two conductor so let's recap them so solid copper
class one solid stranded is class two and then we go for fine stranded which we've got in flex
which is our class 5 conductor now if you want to know more about classes of conductors i'll leave
a link in the description to a video i've made on my other YouTube channel efixx where we go through
the different classes of conductor but just for us we just need to know that these are fine stranded
for greater flexibility and actually it's a class five conductor within our flexible cable this
always used to come up as an exam question when talking about flexible cables and comparing it to
the knowledge we've probably acquired when using twin and CPC or twin and earth cables in this
style of cable we're used to having a reduced size CPC so 2.5 neutral 2.5 line and a 1.5 CPC because
we know it doesn't carry current under normal conditions and only for a maximum of five seconds
that learning has been done in previous videos when we bring in a flexible cable and the exam
used to ask this if for instance your flexible cable was 2.5 you'd have a 2.5 neutral a 2.5
line and what size would the and they often call it earth for this one i know that's odd for Gary
to be saying earth but the green and yellow one in here what size would that be now the problem being
you tend to default back to the learning you had on twin and CPC cables and think maybe it's 1.5
in flexible cables all the conductors are the same size so the live conductors
and the in this case earth conductor all the same so if this was one mil this would be one mil and
this would be one mil etc 2.5 2.5 2.5 so when working with flexible cables all the conductors
are the same size the common number of conductors in a flexible cable are 2 core 3 core four core
and five core i've got a couple in front of me here so a two core flexible cable with our brown
and blue conductors for a liner neutral our three core cable here so we're happy with brown blue and
green and yellow for our conductors haven't got the four core but if we look at the five core
we've got the obviously green and yellow for a protective conductor we've got our phase colors
L1 L2 and L3 we're used to brown black grey for those line conductors as well as our blue
neutral so the common number of conductors within a flexible cable are two three four and five core
flexes when working in that college environment we're likely to come across the two and three core
flexible cables especially early on in our study program the two core being here we've seen this
many times on the channel our ceiling rose and pendant joined together by a piece of flex so when
i open it up we can see that actually that is a two core flexible cable that we've got in there so
we know that we don't need a protective conductor in this fitting because the fitting itself is
fully insulated and therefore doesn't require a protective conductor and that's where we've been
using our two core cable when we think about three core cable we're probably thinking about
our plug tops so we've got a plug top here that goes off to an electrical appliance and that
could have three cables in it and we'll look at another one in a moment so as i open this one up
we're used to this sort of situation where when we open it up we can see our three conductors in
there so we've got our line and our fuse we've got our neutral and we've got effectively our
earth there which we tend to call it in this sort of environment and that's got our three cables and
it's what we expect when we open a plug top up and especially when we make one off at college
let's open up another plug this one here again looking at the flex from the outside and the size
of it we're probably thinking this is going to be a three core cable let's open it and have a look
undo this screw and we can access it in there actually that's two core so we've only got our
line and our neutral so you might be thinking Gaz that's wrong that can't be correct because there
is no protective conductor in there we need to look at the appliance itself to work out whether
this is correct so let's put this to one side and have a look at the appliance i've got here
so what i've got here is an electric heater and i've now got to work out whether it needs
a earth connection well it's made of plastic but that can be a red herring so if you look
at your games consoles and TV's they're obviously metallic in places and sometimes they don't need
a protective conductor so if i turn it round onto the back i'm looking for this symbol here
a square within a square that is double insulated
if the electrical item has a square within a square making it double insulated it doesn't
need the earth connection to it so it doesn't need that green and yellow conductor within the flex
i normally set my students up a take home task to go around looking at electrical appliances at home
to work out whether they are double insulated or not and to understand the fact that if they
are double insulated they don't need that green and yellow conductor within the flexible cable
the most common sheath colour of a flex in a domestic dwelling is black and white and the
exam often asks you when you might use one over another well first of all aesthetically sometimes
it's more pleasing to see a black lead to a black telly and obviously this is a white lead
to an extension lead and that's something that we commonly see however the exam likes to think about
maybe a little bit more about the environment so where a lead could possibly be used outside so
an extension reel the likelihood is you'd want the flex to be black because obviously outside
it could get dirty and obviously the white one would get dirty very easily
and inside you're likely to choose the white flex i know a lot of our games consoles and TV's have
black flexes to them but the exam will try and distinguish between the two based on applications
so where a lead is possibly being used outside in a domestic dwelling the extension lead is likely
to be black or an extension lead is used inside of the house it's likely to be white once you get
onto a construction site the colours of these can change based on the voltage within them so where
you see a yellow lead on a construction site the voltage is 110 where you see a blue lead it's 230
and where you see a red extension lead it's 400 and for your exam you're expected to understand
the colors that represent those voltages yellow is 110 blue's 230 and red is 400 volts
let's take a look at the construction of a plug top so you notice that one of the pins is longer
than the other two pins this is your earth pin here and is made of brass as are the other two
pins but you notice on the earth pin there is no coating around the outside so this here this white
section on these ones isn't a change in a material it is a brass pin but it's actually wrapped with
an insulator on the outside so first of all why is the earth pin larger so that's the first thing
so if we look at a socket outlet here we can see that the windows here or the shutters are closed
preventing you from poking anything in there so if i was to bring in my screwdriver i can't actually
access what would be the live parts in here to do so i need to insert something in here and as
i lever it down hopefully we can see those windows open so we can see the fact that now we've opened
those connections well i've used a screwdriver that's not the correct way to do it so let's pull
that back out so what does open those shutters is the longer earth pin so when we position the earth
pin like so when we push it into place it opens those up so we can put in our plug top so that's
the reason why the earth pin is longer in order to open these shutters it's made of brass why is
it made of brass because it's a good conductive material it's also hard and machinable so they've
machined it into this position and it doesn't have a reaction to copper so in other words you'll talk
about dissimilar metals as you go through your course if i was to screw into a brass terminal a
copper conductor which i will because we've seen that obviously these are fine stranded copper
there is no reaction between the two that could cause corrosion so that's why brass is used good
conductor hard machinable and the fact that it has no chemical reaction with the copper
if we look now at an older plug top i'll bring this one in i've done well to save this one very
similar design so if you look at it we can see the earth pin is larger than the two live connections
exactly the same as we have before but hopefully you've subtly noticed the fact there is no sheath
around the lower part or insulating material around the lower part of the live pins
that we've got on this one here now the problem with these is people with very young fingers
small hands ladies with small hands gentlemen with small hands with these style of older plug
tops there was an issue i'll try and demonstrate it to you so in this position here as we insert it
we can see the windows are open and we've now made an electrical connection there
now my fingers can't touch those live parts however if you were a child or
had smaller hands you could actually get in and as you put your plug top in
touch those live pins and receive an electric shock because it's conducting electricity of
that part if we bring back our original plug top our newer style one we can see when we start to
be in that position just there where we would be conducting all you can see on the live pins
is the white which is obviously the insulated material so if your fingers were in there touching
the pins you'd actually be touching the insulator and therefore you wouldn't receive electric shock
there was a big push to replace these some years ago as portable appliance testing was carried out
in installations such as in the workplace and one of the things they did was remove these from
service because of that reason also the other reason is you have to check the fuse in here
is correct to the appliance so we'll talk about the fuses next so i've opened up my
BS 1363 plug top to reveal the fuse that's in there and the standard size fuse is 13 amps
these are 13 amp plug tops and these are 13 amp socket outlets so the maximum size of fuse that
can go in here is 13 amps the common sizes are 3 5 and 13 however between 1 and 13 they make a number
of fuses but not every size they are BS 1362 fuses and if you can see inside here you've got a metal
end cap both sides it's either a ceramic or glass body this one being ceramic with obviously the
label on it sometimes you see a glass tube between them and believe it or not there's just a piece
of thin copper wire attached between here which is obviously considerably thinner than the conductors
that we've actually used in circuits so they're considerably thinner in the event of an over
current or a short circuit that little fuse while within there will melt in other words will blow
so leading into my next video we'll make a plug top off let's look at how we're going to remove
the outer PVC on the flex the mechanical protection it would be lovely at your college if
you had something like this a tool that's designed on the ends to be used to strip the outer PVC on
flexible cables so we can bring it in and then we can just simply just go round with it so we
go round and then we can just break that off in order that we get the two sections split away
from each other now that would be great well we're not going to get that are we at college so let's
snip that one off and uh maybe that's something you need to buy for yourself a couple of other
methods when i was on site i was taught to use a pair of side cutters and i know some colleges do
so i don't know how long it needs to be to go into a plug top at the minute i'm not worried about
that i just want to work out getting the PVC off and you just take your side cutters and it takes
a little bit of skill to work out to do this you just sort of nibble the outer PVC so around we go
just nibbling as we go once we've got it we can see it bursts open all the way around
and again we've broken away the outer PVC using a pair of side cutters and it wouldn't be Gary if i
didn't suggest that when i was teaching we often used a knife to do this to learn the skills of
how hard to press it so this was a simple case of scoring not sawing so i didn't have it necessarily
on the bench i scored around it and i just folded it in half and just let it burst its way through
so we can see depending on how sharp your knife is got a decent knife at the minute
and then we can pull that off and obviously we've separated the two using a knife so there's
different ways in which we can do it we've taken off the inner PVC around our conductors
again would be great if we had something like this we can see 0.75 to 1.5 and 2.5 we could
just simply bring it in squeeze and hopefully get in the right place just pull it off just
do that again privilege and fluke look how easy that is to strip off the PVC on the conductors
you can use a knife and also you can use a pair of side cuts this is hard and i've showed this
before in other videos if i press too hard and i'm going to strip this one off i just shorten it well
that's no good if i need a desired length so it's all about pressing the right amount of strength
but i don't want to lose any of those fine strands of copper class five conductors you see
they're all there so again practice is the the way to do it isn't it so snip these two off
using a pair of side cutters it's the right amount of pressure just pull away and you can
see we haven't lost those or we can attempt to use our knife this takes a little bit of skill because
obviously we don't want to press too hard because those fine strands on the copper we don't want to
cut ourselves so i've gone round trying to feel for it and then sometimes you can pull it away
with your hands sometimes you take a just pair of pliers and you can just pull it off like that
and again it's just checking that you haven't got any of those coming away i don't want them all
going on the bench they're all still attached so we've got a choice of tools that we can use there
in order to remove the PVC insulating material around these class 5 conductors
this is obviously flat so we can use this style of strippers as well watch this so put my flex in
pull it away i can take off the outside bring it in again i can strip it off for my conductors so
that's incredibly easy we've seen those before for twin and earth cables but as this is flat
flat cables you can also use them on this style of stripper so that was super easy as
well that leads me to the next thing which is what i call improving the electrical connection
with a ferrule so these little copper tubes i know they don't look copper because they're
not copper in colour but if i bring in another cable here they do look a little bit more coppery
so on that one so that is a copper tube to improve the electrical connection so when you
screw into class 5 conductors obviously you can weaken those individual strands so how can you
improve it and you sometimes see it when you take a part a plug top off appliance that you've bought
that actually there's little tubes on the conductors they're ferrules so i'll show you how
it works but i'll leave a link in the description to a video i've done my efixx YouTube channel
going all the way through the use of a ferrule and how important it is so it's a gentle twist
it needs to be longer than we need it so slightly longer than i need it
gentle twist bring in the appropriate size ferrule and then i've got a hope that i can
see this to get it on so my eyes are not great just get that end right bring in our ferrule
and hopefully that will go down over the conductors
wind it down you should have a couple of strands a couple of mil of strands
poking out the end so that tube's on you bring in your ferrule crimping tool
put it in and we crimp it up and we can see there we've improved that electrical connection
in other words now we're almost screwing into what is a solid copper tube rather than those
fine stranded ones and you often see those in the manufacturer's end of a plug top so check out that
video i'll leave a link for it in the description so there's plenty of information to take on board
there to go alongside your classroom notes when thinking about flexible cables we can also go on
and look at the sheath and its properties and its applications so if you had an environment
where maybe the load is hot maybe a storage heater or an immersion heater tank the actual properties
of the flex need to be slightly different to deal with that temperature and the On-Site Guide
is a great point of reference for that in our next video we're going to want to make the terminations
into a plug top i've got two different styles of plug top i've got one with a screw where we simply
open up and go into the terminal and one where it needs to be wrapped around which is a little bit
more complicated i'll use it as a stretching exercise with my students at Tresham college