in this video we're going to look at the conductors that need to be present
and connected before we can carry out our insulation resistance test yes that's correct
there are certain conductors that need to be there and terminated before we can carry out our test
often at college we're working on small wooden boards and the precautions with
insulation resistance is that we're thinking about maybe removing all loads so in other words
disconnecting our lamps our neon's and unplugging things from socket outlets
making sure all our covers are on screwed back and our switches are left in the on position before
we start our installation resistance test but when we step back from that and look at our rig
actually the conductors that should be connected during this test on our small wooden boards won't
be present as we move through our level one two three and onto our apprenticeships it's important
that we understand there are certain elements that need to be in place before carrying out this test
in order to help us we'll look in the On-Site Guide as well as using this test rig
so we can see the conductors that actually need to be in place before carrying out the test
i've got one of my test rigs here and i've disconnected the six mil cable that i've
maybe tested for continuity CPC and polarity and it might be a case now i'm thinking what i
can do now is carry out the insulation resistance test with it disconnected from the consumer unit
and i might want to do that because some other things in here that raise concerns when carrying
out the test if you look in the On-Site Guide it says about making sure your SPD's are disconnected
when carrying out your insulation resistance test as well as RCD's because they contain electronic
components so if we look here we've got a row of RCBO's which will obviously have electronic
components in the circuit i've disconnected also has a ton of electronics in it because this is an
AFDD so effectively it's got a mini computer inside here and the last thing i'd want to do
is pass 500 volts through it and potentially damage it so i'm thinking i'll just leave
it disconnected i'll carry out my insulation resistance test and then i'll reconnect it and
torque up the settings accordingly well that could be the case and you can do that but one of the
conductors will need to be in place so you should look at the consumer unit you can see i've got no
supply coming into here there's no feed in exactly the same as the images shown in the On-Site Guide
and i've got all three conductors disconnected but one of these conductors needs to be in place and
that one being the circuit protective conductor needs connecting to my earth bar and my earth bar
needs connecting to my external earth source so i've got in this case my 16 mil earthing conductor
that will go down maybe to pick up my combined neutral earth on a TN-C-S earthing arrangement
or onto the sheath of the cable on a TN-S earthing arrangement so that must be in place
as well as any protective bonding well there's no protective bonding in here to gas and water but it
could be that this earthing conductor goes down to an MET and the MET has more bonding in place
so i must connect this conductor to the earth bar which is connected to the source earth as well as
any protective bonding before carrying out my insulation resistance test i can then carry
out my insulation resistance test with these conductors disconnected removing anything that
i'm worried about down here SPD's AFDD's RCBO's etcetera in order that i can carry out that test
but it's vitally important that this conductor is in place and connected to the earth source
so let's see what that is said in BS7671 On-Site Guide the first book i get all my learners to buy
is the On-Site Guide remember when you're watching this video it may have changed edition to make
sure you get the latest edition currently this is 2018 and it's blue it may have changed but we're
still going to be looking inside our On-Site Guide at the latest edition i'm going to turn to section
10 which is guidance on testing our installations i've blown up the pages i want to show you
i want to show you the pictures and how they lead to a story about our insulation resistance testing
so we've got here first of all a list that we need to come very familiar with is our test sequence
list starting with a continuity of our protective conductors including the main and protective bond
in other words the continuity of green and yellow conductors continuity of ring final circuits
including the protective conductors insulation resistance polarity and they're the four tests
that we concentrate on our early studies on and we're going to be looking obviously at
this third test insulation resistance but let's just go through pictorially what the On-Site
Guide shows us for the previous tests first so down here we've got our continuity method
there's two different ways in which we can do it we can see we've got a temporary link and
we're measuring our continuity very similar to what we do in the workshop and obviously
we operate switches for polarity but polarity is actually that fourth test and we know that
from the classroom but when we look inside that consumer unit there's very little stuff installed
so it's really just that outgoing circuit there's no earthing conductor and no tails in this picture
so let's go and look at the next page in the On-Site Guide it shows us a different method
this time with a long lead in order to prove our continuity of our protective conductors it's
another method and again i consumer units only got that outgoing circuit so it's give you two
methods of doing our continuity testing before we move on to the next test in our sequence which is
our continuity of ring final circuits and we know we do that as an end to end test on our conductors
and then we go through the process of making some calculations and testing every socket outlet
so we move it onto our next page we can see again this figure of eight comes into play and we start
following the On Site Guide and carrying out that test and through we go to this image here
and then we should be completing that test no consumer unit it showed in these images
but next we're going to be doing the insulation resistance test so let's move on to that one next
so insulation resistance test picture image here is completely different okay so all of
a sudden now from the previous drawing we've actually added some stuff in we've added in our
earth in conductor so often we talk about that being 16 millimetres square don't we
in a domestic dwelling but it can be other sizes so that's our earth in conductor
and we've got a protective bonding conductor coming down to say metallic water pipe okay so
both of those are now pictorially been installed you'll notice still there's no supply cable so in
order to carry out our insulation resistance test we're going to need to make sure our source earth
is in place as well as any protective bonding that's a subtle difference between the drawings
one thing that also cracks me up though is the covers are off on the lighting points my students
would always say to me Gary you told me we have to have all covers on in order to do our insulation
resistance test and yeah that is correct but it's often missed isn't it you can see there
that that's been installed and has to be in place during the test we come on to the next page you
can see some bits in here i get to highlight with my students i get to do the circuits of 400 and
230 volts are tested at 500 volts DC minimum insulation resistance test of 1 one megaohm
further investigation at two making sure SPD's and RCD's are taken into consideration disconnected
okay and we highlight these bits within our work and we come down and we look here
our insulation resistance test carries on again we're testing between different conductors now
but when you do read the text within here it talks about connecting live conductors together
and testing them to our protective conductor and i've done a separate video on how to link
together live conductors live conductors remember being line and neutral together and testing
them to our protective conductor and it will discuss that in here when you read through it
and we look here we've tested again but look we're doing now just our neutral to our protective
conductor yet when you read the text in here it suggests that you should be testing live
conductors to here to the protective conductor so in other words it should be line and neutral i'd
love your thoughts on that and like i said i'll leave a link to the video that i've made on it
and if we look here this is the killer this is the bit here we've got a couple of footnotes here
the earthing and bonding connections are in place the earthing conductor must be connected to the
main earth terminal and means of earthing whilst testing and that's the one thing we probably don't
do at college doing we don't have it connected to our external earth source and protective bonding
when we're working on small wooden boards so if we wanted to carry our insulation resistance test
with our conductors disconnected because we're worried about something in here we can do it as
long as the disconnected conductors are only our live conductors and this is line and neutral link
them together and i'm going to be testing to the earth bar where my CPC is connected
as well as the external earth source and any protective bonding now i can carry out the
insulation resistance test i can press and hold my button and i've got a reading greater than the
machine can read greater than 999 megaohms if i want to do it between live conductors that's fine
just disconnect those and we can test between our live conductors line and neutral again and we
record our reading again greater than the machine can read the important bit there was the fact that
my circuit protective conductor was connected to my external earth source and protective
bonding during the insulation resistance test it didn't matter that these were disconnected
if i was worried about some devices that were installed in here maybe the AFDD's or the surge
protection device i could have connected them and i could have just probed into the top as
well and carried out my insulation resistance test as long as i had these in the off position
but i know people get a little bit nervous with the amount of electronics now in circuit and how
complicated consumer units are becoming that maybe moving forward people were going to decide maybe
to disconnect their live conductors and carry out their insulation resistance test or they're
doing it as part of the installation process of the consumer unit so when you've got your
cables coming through here and you're stripping them you're thinking well i'll do my insulation
resistance test at that stage before i connect it to my devices which you still can do as long
as the earth bar has the appropriate connections in it that we've discussed in this video in order
that you can carry it out correctly hopefully now whilst you're training you can stop and step back
and reflect at the job you're installing maybe on a small wooden board turn to your instructor and
say i know in the real world that i would have to have my earthing conductor connected within
my consumer unit and connected to the external earth source in order that i'm carrying out my
insulation resistance test correctly but as always i hope this video has been some help