so in this video presentation we're going to go back and look at the three plate loop in
method and the connections in the ceiling rose and the consumer units and one way switches
Joe so we've pulled the camera in and we're looking at the consumer unit first the circuit
we've wired or mimicked is three batten lamp holders one way controlled by three switches
can you just go through the connections for me please i see we're using a miniature RCBO 6 amps
type B and rated at 30 milliamps this is just an ordinary 100 amp main switch what we've then got
here the RCBO now you'll notice in the top of the RCBO there's two connections one for the line and
one for the neutral remember an RCD operates by monitoring the current flowing through the line
and back down the neutral again if that current is the same then the RCD is happy if it starts
to see that there is less current in the neutral than there is in the line conductor for example
it knows that current is leaking somewhere either through an earth conductor or through a person
and it knows that it's time to trip so you can see from the top there there's our line connection
there's our neutral connection and then right tucked at the back here there's a neutral
connection coming out and that goes from the RCBO and onto the neutral bar we can also see there's
an A type RCD and we've identified the circuits with number one on the line neutral and circuit
protective conductor for ease of installation and ease of identification during say fault
finding or removal of circuits we now know all domestic lighting circuits regardless of how the
wiring system has been installed needs additional protection by an RCD rated at 30 milliamps or less
can you just explain what we're trying to mimic here as a circuit yeah so what we're looking at
here is this might be a typical domestic lighting circuit let's say it's the upstairs lighting on a
domestic property so what we've got although the cable runs are a lot shorter than they would be
in the real world all of the connections and all of the principles remain exactly the same
so first of all what we're doing is we're taking a one millimeter squared conductor
and that is coming from our consumer unit to our first lighting point so let's call
this bedroom one okay within this conductor we've got a line conductor and a neutral and
that comes up to here those are permanently live cables so there's no switching taking place yet
from this point we then continue with a permanent line in neutral to the light in bedroom two and
then to the light in say bedroom three from each lighting point we then drop down to the switch
and we drop down with a twin brown in this case now it is possible to do this with a brown
and blue conductor however that blue conductor must have some brown sleeving on it to indicate
that it is a line conductor and not a neutral so this picks up the permanent line from inside the
light fitting it goes down to the switch the switch then makes or breaks the line conductor
onto the switching line which then comes back up and into the switch line terminal
inside the light fitting therefore this switch will then operate the lighting circuit if we
look inside the back of the ceiling rose where the batten lamp holder is connected we can see
this is our incoming cable Joe coming up to the first floor into light one saying bedroom number
one so we're bringing in a neutral conductor and a permanent line conductor the trick now
is that the permanent line conductor in this case from the consumer unit goes in a terminal marked
loop our neutral conductor goes in the terminals marked N and then we've got to look at bringing a
second cable down here which is going to come down to our switch this is the twin brown you discussed
earlier so the twin brown will take a permanent line out of loop and a returning switching line
which goes in L okay it's a bit confusing L is really a switching line conductor in order to
turn on the light fitting itself we can now see the lamp has connected to one side of it
a neutral and the other side of it a controlled switching line allowing us from the one way
switch below to turn on and off the lighting point in order to make the circuit safe
we have a circuit protective conductor connected in the terminal marked with a
earth symbol where they're all housed together so all the CPCs are in one terminal
this doesn't require a CPC as it's made of plastic but could be later to turn for an exposed
conductive part such as a metallic light fitting the other neutral the other line in the loop
and the other CPC is the continuation of a permanent line from loop the neutral and
circuit protective conductor on the outgoing cable in this case we're mimicking it going to
another bedroom so that would take a permanent line and neutral and CPC and we repeat the process
of what we've done inside here as we've previously discussed in the classroom these type of bayonet
cap lamp holders have no polarity so as we look at the two pins in there it doesn't matter which one
is connected to line and which one's connected to neutral and we've discussed in the classroom about
Edison screw and the polarity on those the cable is now dropped down from the ceiling rose above
and this is the twin brown and CPC cable that we discussed so one of these conductors here
of the twin brown will be in the common and bringing down the permanent line connection
and one of them will be the returning switching line conductor which we're connecting in the L
section of the batten lamp holder and ceiling rose remember that l is for really switching
line we've secured a CPC into the back of the box again because it's fully insulated the CPC is not
required but is there in case we change it for an exposed conductive part the cable size is one
millimeter squared for all conductors including the CPC in this cable the switch itself is a one
gang one way so as we look at it here on the other switch we can see one gang for one switch on the
front and as we turn it over we can see we've got a connection between common and now one making it
a one gang one way switch i've moved across to lighting point two we discussed just a moment
ago this cable here bringing in our permanent line connection which is connected in loop
our neutral connection connected into the neutral and our CPC connected here with the other circuit
protective conductors again the conductors are all one millimeter squared and we repeat the
process again so one of these brown conductors will be coming down to the switch one of them
will be coming back from the switch and connected in what's called L but which is a switching line
and we repeat the process again going out with a neutral and permanent line remember
all those cables also have a circuit protective conductor and the process repeats itself again
we're at the last point on our lighting circuit but i can see some subtle differences here can you
tell me what's going on so here you can see we've brought our cable from the previous light fitting
into this light fitting but inside here you'll notice that we seem to be missing some conductors
now the reason for this is we've technically reached the end of the circuit so what's
happened here we've brought our permanent live in and that's going into the loop terminal
we've brought our neutral in and that goes into the neutral terminal but we're not wiring another
light fitting off this one and therefore there's no need to take another permanent line neutral and
CPC out of the circuit the other key point that you may notice in here is this conductor here so
here we've got a blue conductor so our brain would normally go that's a neutral but you'll notice
that it's got some brown sleeving on it now that brown sleeving indicates that this what would be
classed as a neutral conductor is actually acting as a line conductor now so this is designed to act
as a line now the reason for that this is just to illustrate a point that it is both possible
and permissible to use a brown and blue conductor as our switch drop running down to our switch here
however if a brown and blue conductor is used then it's very important that this blue conductor
has brown sleeving over it to show anybody who comes back to this installation
that this conductor is actually acting as a line conductor and not a neutral so that brown sleeving
is very very important other than that this cable is just acting purely like a twin brown is picking
up the permanent line it's taking it down to the switch where the switch will then make or break
the conductor onto the switching line conductor which in this case is the blue over-sleeved with
brown which goes into our live terminal and we'll operate the lamp so we're down at that
final light switch and we can clearly see now the blue conductor has been over sleeved with brown
in order to identify it as a switching line conductor and we can see the brown conductor
coming into the common as well so we can see how twin and CPC cable can be used at switch drops
and commonly is in industry at college we tend to use twin brown but be aware that in industry
the likelihood is that you'll be using twinning CPC at switches and identifying it both ends
with brown sleeving please note as well the top of the electric enclosure has had its IP rating
confirmed back to IP4X so object exceeding one mill cannot enter in other words dust and debris
can't fall in and that's the same for all of them as we go along often at college we can't do that
because obviously these boxes are temporarily installed marked and the installation removed