one of my previous presentations we used this rig to confirm that the exposed conductive part was
connected to the CPC and therefore connected to earth so we confirmed things like the metal light
switches and the metallic light fittings had a connection to the CPC we carried out continuity
CPC and polarity we left the circuit in the on position and now we're almost ready to carry out
insulation resistance testing we need to remove all loads there is no lamp in the bulkhead fitting
no lamp here but at the moment i've still got the cover off on the fluorescent light fin
itself we know for insulation resistance test all covers must be on we also know
that the earthen conductor in the tails needs to connect into the external earth source which it is
so i've left the cover off on the flesh and light fin because not all loads are removed
we've got to look in there and see what part of the circuit is still connected
and that is also vulnerable for the test because it's going to be tested at 500 volts DC
and it will need to be removed before starting the insulation resistance test itself so let's
have a look inside that two foot fluorescent light fitting and see what's causing us all the issues
as we look inside our fresh light fitting we can see the connections here for switching line the
circuit protective conductor and the neutral however on the back side of these connections
we've got the cables coming up into here which is our electronic ballast therefore when we
pass our 500 volts through the circuit we'll actually pass it through this bit of kit here
obviously we don't want to do that for a number of reasons obviously it could damage the piece
of equipment also it will give us a false reading for insulation resistance so we're going to need
to either take out it doesn't matter which one we choose the two conductors here for switching
line or the two in here for neutral effectively then removing this part of the circuit here so
the electronic ballast becomes out of circuit i'm going to put those into a connection before
putting the cover on let's do that in the next stage as i just said it wouldn't matter which i
took out so i took out the two neutrals i've put them in an in-short way go make the same style
connect a maintenance-free connector so now we've disconnected the electronic components
from the fitting itself somebody out there is going to say to me well why not take one
of these white uh connecting leads out the back which i can do however my students remove those
several times they're quite fragile they break and then i've got an issue of trying
to replace this leg here so i personally prefer especially my colleagues to remove the conductors
in circuit and put them in this case an inshore maintenance free connector block what i'm going
to do now is obviously pop this back inside and put the cover back on and then we're going to
carry out our insulation resistance test with the electronic components within the fitting removed
so let's summarize what we're up to before carrying out the insulation resistance test we did
our continuity CPC in polarity left the switches in the on position we've removed all loads no
lamps are in circuit however we had an additional loading effect which was the electronic ballast
within our two fluorescent light fitting in order to remove that we could have taken out either the
switching line or the neutrals within there we decided to take out the two neutrals we put in a
maintenance free inshore connector and we popped the cover back on the fluorescent light fitting
itself our external earth source is connected we're ready to carry out the insulation resistance
test within the consumer's unit we must remember however during this test that we have two-way in
this case two-way intermediate switching so we've got a two-way switch intermediate switch and
a two-way switch controlling all three lights so therefore we must remember the trick about
throwing our two two-way switches in order to complete the installation resistance test
let's set up our Megger MFT and let's carry out that test we've carried out insulation resistance
tests many times on this channel but however we still need to check our instrument setup
correctly we're using the red and the green sections in the top of the instrument and we
need to confirm that our leads haven't broken or become damaged so i like to short them together
so we're carrying that insulation resistance test which is in the red scale for mega ohms it's a
230 volt lighting circuit so the test voltage is 500 volts DC so rotate it around to 500 volts and
i'm going to short my leads together to prove that they have continuity so we should get a dead short
and we've effectively got zero zero zero which is a dead short so our instrument's
ready to carry out the insulation resistance test so let's do that next
so let's recap then the Megger MFT has been set to 500 volts in the scale four megaohms
we're carrying that insulation resistance test our consumer unit is isolated also the tails
are isolated they're not actually connected to the supply but we do have to ensure for an insulation
resistance test our earthing conductor is connected to the supply authority's earth
we've got no RCD protection in this circuit we don't need any additional protection for
an RCD because it's not a domestic dwelling and our surface wiring system in plastic conduit
and lights is one that we're suggesting is in a commercial or industrial environment so no RCD
protections we've got any electronic devices from our RCD however main switch and circuit breaker
off doing the outgoing circuit and we're going to test between line and neutral neutral and our CPC
and our CPC in our line in any order that we like so if i click on first of all to the neutral bar
and then i'm going to clip onto the top of the circuit breaker press and hold my tester
i've got a reading greater than 999 megohms i'm now going to test between
neutral and my earth bar press and hold my tester
and now i'm going to test between the earth bar and neutral
and for the third time i get a reading greater than 999 megohms we know the smallest acceptable
value of insulation resistance is one mega ohm or one million ohms we know further investigation is
required when it falls to a level of two mega ohms and below brand new installation we expect the
insulation material around the conductors to be in fantastic condition and have a very high reading
of which we achieved during the test however it isn't complete because in this installation
we have two-way switching in this case two-way intermediate switching so we have to walk back
into the installation throw both two-way switches into the opposite on position and return to the
consumer unit so let's do that next so we carried out the insulation resistance test on the lighting
circuit however it isn't complete because we have two-way and in this case two-way intermediate
switching we must walk back into the installation and go to the two-way switches and throw them
into the opposite on position and then repeat the installation resistance test so we've got
all parts of the circuit tested during insulation resistance if we didn't we would only have picked
up part of the switching circuit by the strappers on the first stage only and we won't have
completed that until we've thrown the two two-way switches into the opposite on position however
we can't walk away from a consumers unit that is potentially live in other words the point at the
top of the double pole switch the tails may well be live we couldn't walk away without returning
the cover so we must put the consuming cover back on if the consumer unit has any live parts in it
i consuming it doesn't we have got the tails connected but the supply authorities haven't
connected the supply to the meter and equipment at the moment so we're okay to walk away from it but
just bear in mind as we move through our studies through level one level two and level three
that no point can you walk away from a consumer's unit that is live with the cover off
so we walk into the installation for ours we go to the two way switch we turn it off we go to
the second two-way switch we turn it back on we walk back to the consumer's unit and repeat the
installation resistance test again and therefore confirming that we've tested all parts of the
lighting circuit for an insulation resistance test and only at that stage can we record the results
for that part of the circuit let's go back to the consumers unit and do that so we've gone out into
the installation we've thrown the two two-way switches back into the opposite on position
meaning the other part the strapper circuit is now in and requires insulation resistance testing
so we're back into consume unit as before we'll go between the neutral bar top of the breaker first
got a reading greater than 999 megohms
between the CPC and line greater than 999 megohms and then finally between the
neutral bar and the earth bar and we've got a reading greater than 999 mega ohms
we now can confirm that the insulation resistance testers have been completed due to the fact that
we have carried out the insulation resistance test in both on positions for the two way switching
we've discussed it many times in other presentations but it's still good to run over it
again so we've finished the insulation resistance test we've ensured the electronic components
in the two-foot fluorescent light fitting were removed the electronic ballast was disconnected
when we removed the two neutrals in the first part of the presentation we did the insulation
resistance test twice we did it on in the first position we threw both two-way switches to get
it on in a second position so all parts of the circuit were insulation resistance tested before
moving now on to another test we must ensure in this case the two neutrals are reconnected in
the fluorescent light fitting and then we can move on i hope this video has been some help