so at the final stage of our basic lighting circuits we've extended it from one way
onto two way and now finally onto two way and intermediate and as before we're going
to carry out the continuity of CPC test and polarity we're going to follow it off by the
insulation resistance and then our circuit is going to go live and we can do some basic
live testing recheck polarity does it work and functional testing do the switches open
and close the circuit so before we start we'll do the continuity CPC test set the instrument
up as we've stated previously so i've set it on to the ohm scale which on the megger mft
is in the orange scale and we're going to need to remove the resistance of our link
so we've stated this in previous video presentations i'm going to link together
the crocodile clips which are in the red and green sections in the top of the instrument we've talked
about before the instrument automatically starts so we're reading an ohm reading now
press the test button so we're reading press test button again and we've now gone to zero remember
if it's flashing zero it's below zero it needs to press the test button at least one more time so
we're going to link together now in the consumer unit the line conductor and the earth bar to pick
up the CPC so we're linking together the line and the earth bar and we're going to go and test that
the furthest point on circuit which believe it or not is the lighting point just to remind you
the line conductor comes through into the loop comes down on our twin brown and then works its
way through the switching line conductors depending on which configuration we're in
until it returns back to the lighting point making the maximum amount of cable being at the lighting
point and it is the furthest point on circuit however we record the highest reading wherever
we achieve it and we should see when testing at the lighting point that our reading will change
depending on how much of the switching circuit we have in so we only need to make a mental
note of the highest reading at that lighting point before we drop down to do continuity at the switch
middle switch and last switch so we're gonna do the continuity cpc at the light fitting as usual
checking polarity at the same time does it come on and off remember the highest reading drop down
to each switch in turn again remember the highest reading and record whichever reading that is under
our box heading R1 plus R2 R1 representing the resistance of the line conductor R2 representing
the resistance of the CPC if it does come on and off as we go through the switching sequence we can
also tick the polarity box and then we can move on to our insulation resistance test once the
covers have been reinstalled so let's get on with the continuity of CPC and polarity combined test
next so we're going to connect on to our earth terminal which is securing into position our
circuit protective conductors and we are going on to the switching line within the actual batten
lamp holder we discussed previously why we're not coming in here we've only been here seven weeks
so i'm on to my switching line within my batten lamp holder i'm currently in the on position with
a reading of 0.54 of an ohm i hopefully can turn it off now so i'm gone greater than the scales
we've got full scale deflection hopefully turn it back on i've now got slightly less at 0.51 back on
now we've got 0.55 and then off again so i've run through from first switch through and then
back again i don't operate each switch in turn you turn one off or on whichever way it is and go to
the next switch to the next switch and back again i need to leave the circuit in the on position so
let's turn it on at any switch and our reading is the highest one we've achieved of zero point
five seven five six and we've proved that these switches turn on and off the light fitting itself
so therefore we've proved polarity but we've still got to prove continuity of CPC at each individual
switch and whichever reading we get wherever it is we will record the highest one so we've got
about 0.55 of an ohm as our highest reading let's do it at each switch in turn next so drop down to
my first switch and i just need to pick up a line conductor and the earth terminal where the CPC is
connected and i've got a reading of 0.29 of an ohm which is lower than the reading i achieved above
so we now move to the second switch so we come to the second switch which is our intermediate switch
we're going to pick up the line connection and a connection for the CPC and we've got to reading of
settles down 0.23 of an ohm which is lower than the reading we achieved at the lighting point
we move to the last switch which is a two way switch again we pick up a line in the CPC and
we get a reading of 0.27 of an ohm so we have achieved the highest reading in circuit at the
lighting point we've proved polarity by operating the switches and leaving them in the on position
we're now ready to move on to our insulation resistance test once we've put all the covers
back on and ensure that all loads are removed so let's do that next so we've completed our
continuity of CPC and polarity test we're ready to move on now to do our insulation resistance test
as stated before we need to turn our instrument into the mega ohm scale and set it to 500 volts
DC we've also inserted as before our leads into the green and red sections of our megger MFT
once again we could have used the blue lead but we've chosen to use the red and green lead
we're going to short the leads together to ensure that we have continuity of
those leads so we should get a dead short on the insulation resistance test we have
proving that the leads themselves i said they they can can snap here without actually seeing them
physically snap they can come disconnected there so we've proved we have continuity of our leads
by shorten them together and we're ready almost to start our insulation resistance test
we must ensure that our switches have been left on we did during the continuity test and we've got in
this case they're all down that doesn't need to be for two way intermediate the down throw to be
on that could be in any combination of up and down but we've left them on during the continuity test
we must remove all loads so the lamp itself needs to be removed before we start the test
and also any sensitive electronic devices in this case we've got the RCCB we must ensure that that
is in the off position and we must ensure the circuit breaker is also off because we said
before the test doesn't need to go out and do the circuit and actually pass it back through
the circuit breaker and across the bottom of the RCCB so the supply is isolated we're ready to do
the insulation resistance test so let's move on to that test so there's no particular order in which
we did the test so i'm going to clip on first of all onto my earth bar and i'll test between that
and the top of the circuit breaker trying to keep my arms out of the way and press the test button
and we've got a reading of greater than 999 mega ohms so off the scale of the machine
i'm going to go across and do between the earth and neutral bars press and test and hold it
on greater than 999 mega ohms now i'm going to go between my neutral and my top of my circuit
breaker for the light so neutral and line once again i've got a reading greater than 999 mega
ohms we expect the overall insulation resistance of our consumer unit that's all the circuits
to give us a reading greater than one mega ohm further investigation is required where the
reading falls below two brand new installation with only one circuit we expect it to have a
fantastic reading for insulation resistance we don't expect the insulation to have deteriorated
through time through age through sunlight so UV degradation and perhaps it's been in connected to
something very hot we don't expect to have broken down over time we've got a brand new installation
our insulation resistance should be fantastically high somewhere in the hundreds of mega ohms
however the test is not complete because our installation has two way and two way intermediate
switching so we've got to walk back into the installation now and throw once again both
two way switches into the opposite on position in order that we test the other part of the strapper
so let's do that next so we're not quite complete our insulation resistance tests yet we need to
walk into the installation and find our two way switches and throw them back into the opposite
on position in order that we get the other strap in circuit and then do the installation resistance
test for that circuit again so as we come into our installation we've got a two way switch
intermediate and a two way switch it is only the two way switches that need to be thrown into the
opposite on position it wouldn't matter how many intermediate switches i had we'd leave those alone
we just throw the two two way so if i turn it off here and back on here and now i can go back
to my consumer unit and for that circuit repeat the insulation resistance test again so we come
back to the consumer unit after throwing our two way switches into the other on position
visiting the strap in circuit and again i'll go into the earth bar on top of the line press and
hold my instrument reading greater than 999 mega ohms onto my neutral bar so earth and neutral bar
press and hold the test button a reading greater than 999 mega ohms then move across
i'll do between the neutral and line press and hold i've got a reading greater than 999 mega
ohms i've now completed the insulation resistance test because i've done it in both on positions
if i had 10 20 100 intermediate switches it's still just the two way switches that are thrown
into the opposite on position in order that we get the other strap in circuit and complete
the insulation resistance test so now we've completed the continuity CPC and polarity test
we've done the insulation resistance test twice did it in the first on position we walked out into
the installation through both two way switches and then repeated the insulation resistance test again
we're now at the point where we're going to go live we only do very basic live testing
we check it works again and we're calling that rechecking polarity does the light come on and
off i'll show that in another video presentation and prove the functionality of the switches do
these switches actually turn on and off the light fitting and have we got the ability that the
glorified switch which is the RCBO operates from on to off and our circuit breaker also will open
and close the circuit itself seeing it go on and off so they're glorified switches in the consumer
unit and we'll pick that up on functional testing i hope this video has been some help
you