at last back into a cubicle a lighting circuit has been installed and what i'm going to carry
out today joe so today we're going to carry out the first of the dead tests
and according to BS 7671 that is the continuity of CPC yeah there are two methods that we could
use and in this video we're going to consider the R2 method not the most commonly used method
for lighting circuits guys what what's the rt method normally used for yeah the continuity of
the protective conductor's been the first test we carry now and the R2 method is generally the one
used when we're trying to measure the resistance of the protective bonding to gas to water and oil
okay so that's when we use that in this case we're doing test one continuity but we're not going to
include test four what's test four so test four is polarity now if we were to use the other
continuity of CPC test method commonly known as R1 plus R2 which we will review in another video
when you do the R1 plus R2 method you do you can prove polarity at the same time as doing that test
but with the R2 method that we're going to look at in this video we're not going to be able to
prove that so we would need to go back at some point and do that polarity test okay so we're
going to use our long wandering lead we're going to need to remove the resistance of that lead and
we're going to take our probe and go to the CPC which is connected in every light switch and that
every light fit in however there's some extra considerations of the fluorescent light fitting
Joe what are they yeah so this light fitting this fluorescent has a metal body and because it's made
out of metal that means it's not double insulated in this case so that means that this metal
body is an exposed conductive part so what we're going to do is we're going to prove that the CPC
is continuous not just to the terminal inside there but also to the actual metal work and that
way we can be sure that this is connected to earth yeah and that's deadly important in it there's no
point proving the CPC only gets the connector block within the fitting itself we've actually
made sure it gets to the exposed conductive part as well during this test so we're going to remove
the resistance of the lead we're going to bring the camera in and look at carrying on that test
okay then Gary so we've got a couple of bits and bobs here so we've got our
long wandering lead over here and we've got our multi-function tester over here so what are we
going to do before we actually start doing the test so we set our probes up i've disconnected
the probe from the Megger MFT and inserted into the side of the long wandering lead
i've unraveled my lead however i'm going to need to remove the resistance of this
50 meter long wandering lead and the leads that come with the mega MFT i need to set it to ohms
for the instrument to come on and we're going to do as we always do is link the two together
and press nice and firm into place and we need to remove the resistance of those leads
just press it once press it twice and we've got zero now so what we've done is remove the
resistance of the long wandering lead and our test leads and we're now ready to carry out that test
so any test that we do now it won't take into account the that measurement there it'll just
be the true measurement of the resistance of the CPC it will and therefore we can record
that as R2 in our test paperwork measured in homes fantastic right let's do the test
so then guys we've got the meter all set up ready to test so talk us through the R2 test method so
we've got the CPC here connected into our earthing terminal within a consumer's unit we're going to
take one of our leads and use the green one with a crocodile clip on and clip it onto the actual
earth bar where the CPC is connected i'm now going to take my other probe out into circuit
and i'm going to probe onto the CPC's wherever we find them and at the first switch we can see
the CPC is connected into the back of the box and we're going to probe onto the CPC just here
we get a reading of 0.12 ohms so 0.12 ohms goes so we've got an R2 reading should we just record that
in our test schedule and move on to the next test now we need to test at all points in this case
in the radial circuit so we're going to test at every lighting point and every light switch point
in order to prove the CPC is at those locations recording the highest reading wherever we find it
fantastic key point that recording the highest reading we need to remember that moving forward
and that will be recorded in the test paperwork under the box heading R2
lovely right so we'll move on to the next test point so what we're up to now joe so what we're
going to do now is we're going to head out into our installation we're going to start doing some
testing at other points we're going to leave our croc clip on the main earth bar within our
consumer unit we've uh just plonked the long test lead onto the floor there that can just stay there
while we take the other end of that out into the installation and we've got our test meter
which we'd take with us so that we can see the readings so we'll come to our first light
fitting that we're going to test from now as we said in our introductory part of the video this
is a fluorescent light fitting it's got a metal clad body which means that this body in this case
is forming an exposed conductive part so we've got to prove that we're getting continuity to
the metal work on the box as well as to the terminal so let's prove that we've got it to
the terminal first of all so i'll just plonk the other end of my test probe onto there and on the
meter we get a reading of 0.03 of an ohm so we've got a nice low reading there not 0.03 of known
but there could be a situation inside an item such as this where the on the inside of the fitting
the CPC connection could be lost here it's a it's a metal tag that the CPC terminal screws onto
but of course that could well become disconnected at some point we just want to make absolutely
sure that we get a reading so we've got a little bit of metal here where we can test to
so if i put my probe onto the actual body work of the fluorescent fitting you can see that we're
still getting our naught point not three reading which is really nice so that means now we can be
confident not only does the CPC uh continue all the way through the circuit to the light fitting
but also the actual metal work of the black box is also connected uh via the CPC to earth so we've
approved the exposed conductive part is connected to us absolutely so joe in real terms we've moved
to a different room in the installation and we're going to carry out the test again at this point
that's correct this light fitting is all plastic so there's no metal body work to test to at any
point so we're just going to test to the actual earth terminal and make sure the CPC is continuous
to that point so i'll put my probe on there we should get a reading on the meter now what reading
is that guys got a reading of 0.09 of a gnome okay so we've taken three different readings so far
and we need to bear in mind that whatever reading is the highest is the reading that we record so
we've proved that the CPC is continuous to these fittings and to the switch but so far the highest
reading is 0.13 of an ohm so unless we get anything higher that'll be the one we record
let's check the other switches now so guys we've tested at three different points so far so what
are we going to do next we're at one of the last three points that we've got to test so we've got
three switches left to test in circuit they're fully insulated the CPC is connected to the earth
terminal at the back so i'm going to probe on to that and i've in this case got a reading of 0.1
ohms i'm going to move to the next switch again onto the earth terminal in the back of the box
and i've got a reading of 0.17 of an o and then to the final point that i
need to test that let's see what reading we get there get a reading of 0.25 of an ohm
so when we did that test we got a number of different readings Gaz which one of those readings
are we going to record in our test paperwork we always look to record the highest reading for
our continuity test the highest reading being 0.25 of the ohm and we need to make sure we record it
in the right place in the paperwork what part of the paperwork can we record it under so we
would record it as a box marked continuity of CPC and under that there is a split into two columns
and we would record it under the column marked R2 we would write 0.25 for this particular lighting
circuit that's because we've measured just the resistance of the circuit protective conductor
hence we've recorded under the r2 box we haven't included any of the tests nope so we are at some
point on this particular test method we're going to have to go back when we get to step
four in the testing procedure and carry out our polarity test we haven't proved polarity on this
circuit just yet no we haven't we're going to do another video where we do a combined
test for continuity CPC and polarity but today we wanted to prove that you could measure just
the continuity of CPC using the long wandering lead and really using the R2 method which they
call it in industry don't they absolutely so we hope this video has been some help