in this video we are going to carry out the continuity of CPC and polarity tests for a
lighting circuit i'm going to perform it on the first lighting circuit we carry out in the
workshop which is a one way lighting circuit i'm also going to introduce the R1R2 link
which i've reviewed on the channel before to see if it can make this test easier in that college
setting and maybe if you're not in a college setting you can leave some comments below whether
you believe it would work well in industry we'll also sign post the pages in the On-Site Guide that
can also be used to help you carry out this test so some of the things i've performed off camera
is i've isolated the consumer unit's main switch and i've proved it's dead in here i've shown that
many times on the channel before and i will leave a link to that video as well the lock is in place
the sign is here and i've got the key inside of my pocket out of the way and i'm ready to perform
this dead test if i look in the On-Site Guide i'm looking in Section 10 of the On-Site Guide
for testing and as i turn over the page hopefully you're familiar with these first tests here ones
that are carried out dead and the first test says continuity of protective conductors including
main and supplementary bonding i said i would also include test number four the polarity test and it
says here by continuity method so you can include this in stage one testing and we will if we look
across at the page here you've got a pictorial clue on how to carry out the test so we can read
the description above and we can see there is a temporary link from the top of the circuit being
tested to the earth bar where the CPC is connected and that's what we're going to use with our R1R2
link we're going to make that temporary link shown in this one here and we'll include that polarity
test at the same time so i've got my Megger 1711 multi function tester one i've used many times on
the channel before i've put my leads into the top of the instrument and i'm using the red and green
section and as always we've used the red and green lead but remember we don't have to they could be
different colours but as always we like to keep them the same we turn it back over we're going to
need to set it to ohms in order to measure the resistance of the cable because the continuity
test is measuring the resistance of the conductors so we're going to flick that round to the omega
symbol our instrument comes on and now we've got to remember the fact that our leads are obviously
got copper cables within them copper conductors so we need to remove the resistance of those
as well as our link our R1R2 link will also need its resistance removing so i'm going to link them
together so crocodile clip on one and crocodile clip on the other you see straight away without
even touching the machine that we've now got a reading on it it is saying zero so that's a little
bit of luck to start with if it was flashing zero we know it's below zero so it's saying that we've
removed the resistance of those leads but let's show you how we would remove those resistance
we press the test button we've pressed it once you can see we have a reading i press it again
and i'm looking for a stationary zero zero zero so that is not flashing therefore i've removed
the resistance of both the link and the leads so i can perform this continuity test where i'm
measuring the resistance of conductors so the circuit under test is this one here this B6 amp
circuit breaker so six amps type B circuit breaker and i'm gonna need to link together the line
and CPC and on the On-Site Guide it shows a link between the two doesn't show you disconnecting
any other elements of the circuit so we're going to link from here to here normally i would have
undone this and put either a crocodile clip onto the conductor over to here or would have taken
this conductor out and screwed into the earth bar to link these two together but with this R1R2 link
it removes the need to do that so from a college point of view it means we aren't undoing screws
more often than we need to especially when testing so i'm going to drop this one in which has got a
magnetic tip on it so i drop that into there to link onto my line conductor and that's held in
place i can't pull that away that's held and i'll just put my clip across to here to link together
my line conductor to my CPC and we're going to measure the resistance of those two
and when we open and close the switch we will be able to prove our polarity that our switch
is operating in that line conductor we've only got one lighting point on the circuit so we're only
going to need to test it to here in the real world if there is 10 lighting points on the circuit so
maybe four bedrooms a landing area an upstairs bathroom etcetera you'd need to do this test at
every single lighting point and switch but in a college setting this time around we've only got
one lighting point and one switch so we need to prove the CPC gets to here and the CPC gets to
the switching circuit but if there was more than one you'd have to continue on the test for all of
the points on the circuit and record the highest reading so if we undo here and we open it up we
can see we've got our connections here hopefully we're familiar with the three plate method from
many videos i've done and time training in college so we've got our circuit protective conductor here
and we're going to be going on to our switching line conductor so we can prove that the switch
will operate in the line conductor it's not a neutral it's got brown sleeving on it is a
switching line and we've covered that many times on the channel so i'm going to measure between
here and here i'm going to look at the reading i'm going to operate the switch to hopefully see
full scale deflection and when i see that full scale deflection i know that switch is operating
so and we come with our connections so we're going to connect onto the protective conductor
we're going to connect onto the switch in line now you may have heard a little click noise
so if we go back to our instrument we can see we've got a reading
and it's going to jump around a little bit let's see what we get 0.09 have a reading therefore we
have continuity is jumping around a little bit so what in other words if we just pull back slightly
we've got a cable from here so the CPC from here comes to here and by connecting
gets all the way back so we have a completed circuit so it will come CPC in down to the switch
from the switch back and round as a complete loop and we've measured that resistance as 0.09
we would record the highest value of reading so we need to remember that one but i said we were going
to perform the polarity check at the same time so we come to the switch i'll operate the switch
i've operated it and we can see now it's an infinite reading it's gone off the scale we have
a lack of continuity so we've broken a conductor naturally we break the line conductor here at
the switch so we open the circuit so if we do the switch again so if i go to that position i've got
a closed circuit i've got a reading now of 0.1 of an ohm so it's there it's jumping around a little
bit so we're back to our original reading of open and close that switch let's do that once more
so we've opened and closed that switch and we look at the instrument deflecting
and we can prove that that switch is operational as part of our polarity check
and i'll read and settle down we need to leave it in the on position for tests that are carried
out in the future we're not going to carry out them in this video but the insulation resistance
test requires all circuits to be left on but we're going to leave it on and we're next going to check
the CPC makes its way down to the switch we also need to prove the CPC gets down to here we can see
it's a fully insulated box and switch so therefore it hasn't got any metallic parts that would make
it an exposed conductive part so this CPC is down here waiting in case maybe the switch has changed
from metallic one and then that would be required to be connected to the CPC but we need to prove it
gets down here because there's nothing suggesting that the minute we've left our installation
that these switches are changed so we need to prove the CPC gets to here so if we clip onto
the connection there in the back of the box and we come into and i'm going to go into the top where
the common is it wouldn't matter because i've left it on which one i go in but i'm into the
top position i'm on to the CPC and i go back and look at my reading i've got a lesser reading here
of 0.06 i do not need to operate the switch there's no operating switch here we operated
the switch to prove it turned the light on and off we don't need to prove the switch comes on and off
we've already done that and the CPC is connected to here and we've got a complete path between the
line and CPC back to our linked position within the consumer unit so we've proved its continuity
we've operated the switch so we've proved polarity we need to record the highest reading
of 0.09 in our box heading R1 plus R2 we've operated the switch and see the circuit open and
close therefore we can tick the polarity box and for us that's it completed for our continuity of
CPC and polarity test for our one way lighting circuit so i'm sure someone's already thought
Gaz that switch is further away from the consumer unit than that lighting point however the highest
reading was here and we know resistance is based around length so longer conductors
have a higher resistance and shorter conductors of the same cross-sectional area so this is a one
millimetre squared cable that went through my light and to my switch so why was the reading
higher at the lighting point than it was at the switch well let's think about the circuit that
we've just measured its resistance for the line connection here comes from the breaker it comes
into the loop in terminal in here and we've looked at that before in the channel it comes into loop
it goes down to the switch and then comes back on the blue conductor identified with brown sleeving
which is my switching line back to here where we measured its resistance when we're at the
lighting point so we measured from the switching line to CPC here with that full length of run in
and achieved our reading so it came line conductor through down and back for measured point to here
when we were measuring the CPC and line connection in the switch down here
we had the line conductor from here so the line conductor came from the consumer unit
it came into the loop terminal and down to that position there and we measured between the common
and our CPC connection so when we did the lighting point we actually had an additional piece of cable
being our switching line conductor back which meant the resistance was higher at the lighting
point because more cable was in circuit than it was at the switch however in your own mind you're
thinking that this switch is further away from the consumer unit than the lighting point which is
true but the amount of cabling circuit is longer when we measured it at the lighting point however
i said to you at the start whichever reading you get which is the highest is the one you recorded
okay we've used logic here to get our highest reading here when you're in a full installation
you're going round it's that highest reading achieved wherever it is that we would record
so hopefully that's give you a guide on how to carry out that first test that you're
probably going to carry out in any electrical workshop up and down the country on the first
circuit that you install which usually is a one way lighting circuit i've used my R1R2 link and
i think i've confirmed from my point of view that this is a must for college settings it meant that
i didn't have to unscrew any additional terminals within my consumer unit that obviously can become
damaged and it's quite expensive for colleges to start replacing items within consumer units
hopefully you've also seen the fact that even though we thought the highest reading may have
come at the switch because it looks further away from the consumer unit then we can see
the length of the conductors at the lighting point testing between the switching line and CPC
has more copper cable in circuit and therefore a higher resistance we know that R1 stands for
the resistance of the line conductor R2 stands for the resistance of the circuit protective conductor
so when we inserted the reading of 0.09 into our paperwork we saw the box heading R1 plus R2
the resistance of the line added to the resistance of the CPC which we achieved by linking them
together within the consumer unit with the R1 plus R2 link we operated the switch to see the
lighting point come on and off with linked between the line conductor and the protective conductor
in the consumer unit and polarity proves that we switch and fuse within that line conductor and we
prove that so we can give that box a tick but as always i just hope this video has been some help
you