so return to the same cubicle we're back with the same lighting circuit last time when we did which
test last time so last time we were doing the continuity of CPC test and we did that using the
long lead method to measure the R2 value of the CPC but we're going to use a different method this
time guys yeah that's not the most common method of actually measuring the continuity of the CPC
in say a lighting circuit so we're going to go on and do the combined continuity of CPC and polarity
tests which we didn't include last time so we didn't include the polarity test last time we're
going to include it this time this means we'll be able to achieve a figure that we'll record in
our test paperwork as yeah we'll record that as R1 plus R2 R1 being the resistance of the line
conductor R2 being the resistance of the CPC we record that in ohms goes in our test paperwork and
then we'll also be able to record the fact that we've done the polarity and what are we putting
the polarity box uh we simply put a tick to prove that polarity is correct so bring the camera in
close we'll set up our Megger mft and we'll get ready for that test okay then guys so before we
carry out the test that we've just spoken about we need to get the meter set up correctly so what
are we going to be thinking about doing here so we've got our Megger mft our multi-functional
tester and as was measuring the continuity of the CPC in this case we're doing R1 plus R2
continuity means we're measuring the resistance of the conductor so we're going to flick it round to
the scale here for ohms and we're going to need to remove the resistance offered up by
the leads themselves and the crocodile clip so if we link those two together with the crocodile clip
so it's important at this stage to make sure that those clips are actually touching the
metal probe at the end of the instrument at the end of the lead so we're reading 0.01 of an ohm
so that looks like it's already zeroed it is it's already zeroed so we give it a quick double check
yep so you press test button once and you see we have a reading press the test button again
and we've actually got zero so we've actually removed the resistance offered up by the leads
and the link before starting the test so now when we carry out the test whatever reading we get on
the screen we know is the actual reading of the conductors and of all the rings we get which one
will record Joe well of course we'll record the highest value for this test let's get on
with the test so we're at the consumer unit end now joe what are we up to in here so what we're
going to do now is we're going to set up the start of the circuit so when we go out to the
rest of the circuit to test our continuity of CPC we're going to make sure that we can get a reading
so what we're going to do is we're going to take our line conductor and we're going to connect it
to the CPC now in this style of consumer unit the Crabtree Starbreaker there's nowhere that i
can actually clip onto the line connection in the circuit breaker so what i've done is i've removed
the line conductor from the circuit breaker and i'm going to connect from there directly
onto the earth bar so by connecting directly onto the earth bar
we've now got a link between the line conductor and the CPC now if this lighting
circuit was installed in earth metallic conduit or something similar we'd have to make sure that we
disconnected the CPC from the earth bar in here so that we didn't get any parallel earth paths going
on with our circuit we'll cover that in much more detail in a later video but at this stage because
there's no chance of parallel earth paths with this circuit we can simply connect it straight
onto the earth bar so with that connection made we're ready to start carrying out our tests and
by linking the line conductor to the CPC we get R1 being the line conductor and R2 being the CPC when
we measure their continuity or resistance of those conductors absolutely spot on so joe we're at
one of the lighting points on the radial lighting circuit and what you're going to carry out for me
so what we're going to do first of all is we're going to carry out the continuity of CPC test
we're going to basically prove that we've got the CPC is continuous to this point in the circuit now
at the minute you can see this is a plastic switch so actually there's no requirement for this to
be connected to the main earthing terminal however down the line it may well be that a homeowner
or a less professional person than ourselves might come along and replace this with a metallic switch
so we want to make sure that we've got that CPC connected all the way through to the circuit
to every switch so all i'm going to do here is test from the CPC terminal to
the line connection at the top of the switch there and then just make a mental note of that reading
so i've got 0.19 of an ohm so now i'm happy that i've got a continuity of CPC reading to
this point in the circuit so we can now move on and test our next point so inside this light
fitting we're going to test between line and CPC just like we did down at the switch but what we've
got to think about here is we've actually got two different kinds of line connection
so here we've got our permanent line connection so those are all permanently live when we turn the
circuit breaker onto this circuit and in the back here we've got the switching line connection now
that's the one that we're going to test on because that will give us a slightly higher reading after
the because we're also measuring the resistance of the conductor all the way down to the switch
and all the way back again so we'll get a slightly higher reading and we're looking for the highest
value of R1 plus R2 on this circuit also by using the switching line which other tests will
be incorporated during the continuity one joe uh we'll also be incorporating polarity into our test
which is obviously an important requirement of the regulations the switch will be left in which
position once you've completed the continuity of CPC and polarity at this lighting point
once the test has been completed we will leave the switch in the on position because that's going to
massively help us with our insulation resistance testing later so what we're up to here so again
we're just going to do the same thing we're proving that we've got a CPC connection up to this
point however there's a couple of things to think about as you say so first of all we want to make
sure not just that we've got the CPC continuous to the earth terminal in the back of this fitting
but we want to make sure that the CPC is also actually connected physically to the metal body
work of this light fitting it's no point just making sure that we've got a CPC connection here
if the outgoing connection to the metal work is dodgy out of this side at this point we can also
prove polarity so we can start to bring in that second test in this combine test so first of all
let's just check that we do have continuity of CPC to this point so i'm going to connect
from the CPC terminal onto the line terminal there and if you pan down and look at the
meter reading there you can see we're getting greater than 99.9 ohms so basically what that
means is that we've got an incredibly high reading because that's actually greater than 99.9 kilo
ohms so we've got a huge unacceptable reading for a CPC measurement so all we've got to do
is flip the switch and once we flip the switch as you can see now we're getting a much better
reading we're getting 0.66 of an ohm so that's what we're looking at there so we're happy that
we've proved polarity we've got the line being switched by the switch rather than the neutral
in this case and what we can now do is just prove beyond the shadow of a doubt that we've actually
got an earth connection to the metal work of the light fitting by connecting onto the back box like
that and you can see there we're getting 0.64 of an ohm 0.63 so again we'll make a mental note of
that value that we took before 0.65 we compare it to our value that we got at the first switch
0.18 and then we can just think about which one of those is now the higher one well obviously it's
0.65 so that's the one we're going to keep in mind unless we get a higher reading so let's move on
and test the next slide so joe we've tested our first lighting point any other considerations
so what we've got to think about now is having completed this first test for this light and this
switch we're going to leave this switch in the on position now the reason for that is that when
we come back to do our insulation resistance test a little bit later down the line we want to test
every scrap of cable every bit of insulation that is within this circuit so by leaving this in the
on position not only will we check the insulation on the permanent side of this switch we will also
check the insulation on the switch line side of the switch there's it's a one-way switch is it
important that we leave it in a certain position for when we screw it back actually to the box we
want to leave it in the on position so can you show us what that looks like then joe please
if the switch has been wired up correctly that should be the on position for a one-way switch
so i'm at the next lighting point in the circuit i'm now using the crocodile clip to clip onto the
earth in terminal where the CPC's are connected and my probe is on the switching line terminal
within the batten lamp holder itself if you look at the instrument we can see we have a reading
a reading of 2.25 ohms indicating the switches in this circuit have been left in the on position
we need to prove polarity so we need to turn on those switches and off those switches in turn
so i'm going to go around and now operate the three switches that control this lighting point
so we should see the instrument hopefully go off come back on must look at the reading the
readings will change depending on the amount of strappers in circuit so we've got a slightly
different reading now slightly lower go to the next switch it's gone off back round again
and then to the final switch however i've left it on off position when it needs to be left
on so therefore i must turn any of the switches in this case it's a two-way intermediate to turn
it back on i need to remember the highest reading i got the highest reading i got during the test
sequence was 2.25 ohms must be left in the on position for the insulation resistance test
that we're carrying out later on so we're down at the switches we've got three final switches
to test for continuity of CPC and a probe into the earth terminal at the back of the
box where the CPC is connected and onto a line connection and we see we have a reading of 1.67
ohms go to the next switch again the earthing terminal at the back into the intermediate switch
and i have a reading of 0.72 and then i'm on to the final two-way switch in this circuit
probing on and have a reading of 1.83 ohms so joe we've completed the continuity of CPC and
combined it with the polarity test you agree yeah absolutely we've got that spot on there and of all
the rings we got which we will record we're going to record the highest reading so for any test that
you carry out a good rule of thumb is you're always looking to record the worst case reading
and in this case the worst case reading would be the highest reading we're going to record that in
the what box headed in our test paper that's going to go under the R1 plus R2 column R1 standing for
the resistance of the line conductor and R2 standing for resistance of the CPC conductor
that leaves us another box that we can also can complete at this stage which is the polarity box
which is the blurry box we're just going to put a tick in the polarity box we don't need to record
any value for that we just put a tick to show that it's been done and verified so that's the
continuity CPC for this line circuit including the polarity test completed yeah and as we've only got
one circuit on this distribution but we don't need to go on and do further continuity test do
you agree yeah absolutely we're quite happy with this circuit on that on that front now
so it just leaves us to go on to a next test and test sequence before this will be insulation
resistance so we're going to do the insulation resistance test next so we're going to get the
covers on we're going to do that in another video presentation we're also going to look at
the possibility of what they would like to see the insulation resistance test done for AM2 and AM2S
with a lighting circuit with more than one switch control and lighting point
yeah so there'll be two slightly different methods that we look at and again we've got to bear in
mind all the time think about the circumstances that you're testing in when you're testing in
the real world you'll carry out the testing to make sure the circuit is completely safe
and that you're comfortable with that but sometimes perhaps in an exam situation
we need to do the testing the way that the examiner is expecting us to do it so
it's important just to bear that in mind moving forward so we'll look at that in the next video
so we're going to end this one year absolutely okay we hope this video has been some help