so we've completed our steel war armored sub main circuit where we have a 60 amp switch fuse feeding
a consumer unit we're trying to simulate perhaps a block of flats where there's several 60 amp switch
fuses in the basement and steel armored cables go up to each floor in turn to feed the consumer unit
within each of the flats we're going to carry out our continuity of CPC and polarity test
and followed by our insulation resistance test in this presentation so i'm getting set up to do my
continuity of CPC and polarity test i've linked together at the tails the line conductor and the
earthing conductor so my circuit passes therefore through my 60 amp switch views and comes all the
way to the furthest point of the radial which is the top connection here of the RCCB for the line
and into the earth bar we're going to also need to confirm that i'm actually using the correct
conductor for my CPC i've used black at this end and hopefully i've used black at that end we've
had issues before where students have got it in reverse at one end they've used black as a circuit
protective conductor and at the other end they've misplaced it and used the grey as a circuit
protective conductor we didn't pick this up when we tested between it connected to the earth bar
and line during the continuity test because we have a parallel path between the two points
the steel wire armour itself also passes a circuit protective conductor from the isolator
to the consumer unit in order to prove polarity i'm asking my learners to disconnect
in this case the black conductor removing the parallel path set up by the armoring
in order that we can also prove polarity so we're going to disconnect the black conductor
from the disconnected black conductor which is our CPC connect our tester between
there and line we've got our tails linked together and we're going to take a reading
we then operate the switch and remove the fuse in order to prove polarity we're then going to
replace the black CPC conductor identified green and yellow sleeving and repeat the test again with
the parallel path of the armouring in we should see the second test as a slightly lower reading
than the first so i've disconnected the circuit protective conductor within the steel wire armour
the core which is black identified with green and yellow sleeving i'm going to test between
the disconnected conductor and the line conductor which is connected in the top of the RCCB by
removing the CPC from the earth bar we removed the parallel path created by the steel wire armored
which can give us a confusing reading for polarity in other words if i'd use the black conductor this
end as my CPC but i'd use the grey conductor at this end we will have created a path between here
and the earth bar if this was connected that would give us a reading for R1 plus R2 so in
order to prove polarity i've disconnected the conductor used for the CPC and we test between
the disconnected conductor and line in order to achieve my R1 plus R2 reader so let's connect onto
the circuit protective conductor and the top of the RCCB i get a reading of 0.05
it settles down 0.05 ohms in order to prove polarity i need to operate the switch
we see the circuit now go off and then hopefully comes back on through full
scale deflection however as this is a double pole switch operating both live conductors
i need to pull the fuse and see the circuit go open again and close in order to prove polarity
polarity proving that we switch and fuse in the line conductor i'm now going to reconnect my black
conductor identified with green and yellow sleeve in as my CPC into my earth bar and repeat the test
again with the parallel path in possibly won't see a smaller reading because the job is very
tiny in length but we should therefore see maybe a change in the reading as we reconnect it in and
we have both the copper conductor and the steel armor in as our circuit protective conductors
let's do that in the next part of the presentation so i've reconnected my black
conductor identified with green and yellow sleeving within the steel wire armour construction
which is now meant that it's gone back into the earth bar which is also picked up through the
fly lead the armoring between both locations as a parallel earth path we should potentially see a
lower reading now for R1 plus R2 our continuity of CPC reading because we've got the copper conductor
and the steel wire armour now as part of the earth path let's connect on and see what we get
i've got a reading of 0.03 again i can prove polarity by operating the switch
when we see the circuit goes off but stated previously we know it's a double pole switch so
it's line and neutral being operated we pull the fuse circuit goes off and reconnect the circuit
so by doing the test in two ways with the disconnected conductor for a first stage R1 plus
R2 continuity of CPC and polarity part of the test we're helping to prove polarity that we haven't
got conductors mixed up one end uses black one end uses grey we've proved that we then reconnected it
into the earth bar to have the parallel path created by the armour armoring and we saw we
had a lower reading for our continuity of CPC we will record the highest reading of 0.06 we suffice
polarity by operating the switch pulling the fuse and confirming the conductor in this case black is
the circuit protective conductor we're now ready to move on to insulation resistance test so this
time we're going to carry out the insulation resistance test from the tails themselves
my students are aware that the earthen conductor needs connecting to the supply authority's earth
and isn't for this test but we're going to go through the sequence of tests anyhow we're going
to connect together in any order we like so we do live conductors first testing at 500 volts DC
we got a reading greater than the machine can read so we went off the scale at 999 megohms
move it around we're going to do line conductor to earthing conductor and we've got the same
reading greater than the machine can read and finally between the earthen conductor and neutral
once again greater than the machine can read we've got the switch
here in the on position we've got the fusing circuit and the RCCB is in the off position
because the electronic components within it and the insulation resistance test has been
completed however the eagle-eyed people amongst you will be stating in the comments to me
why are we earthing the tray when it doesn't need earthing it's neither an exposed nor extraneous
conductive part me and my students have had that conversation and they're fully aware of that
the tray itself does not induce a potential from outside therefore it doesn't require connecting to
earth however the awarding body we're currently working for requires it to be earthed in their
marking criteria hence that they have earthed it they are fully aware that they didn't need to