so i have managed to get out on site and this video will link nicely to videos i have made
recently on the insulation resistance test in BS7671 On-Site Guide it shows you doing
the insulation resistance test with all the circuits at the same time which is almost
impossible when RCDs are inside of the consumer unit in this consumer unit we don't have any
so we can do all the insulation resistance tests from the outgoing side isolated there
the supply has been isolated the outgoing side of that main switch we can do all the
line and neutrals together all the lines and CPC's and all the neutral's CPC's there's
a one test and to help me do that test i've been joined by Marcus today and you're gonna
set up your instrument first for me yes yeah so i've got the Megger 1711 here um we're
going to set it to the insulation resistance setting and we're going to do it on 250 volts
DC first i know it's normally 500 volts but we believe we've took out every appliance
took out every lamp in all of the circuits so but just to be sure we're going to test
it at 250 just to make sure we don't damage anything um if there is something still in
circuit so you're trusting the fact that i've turned the boiler off yes okay so first of
all i'm just going to test my leads together so you linked your leads together so if you
look back here if your leads are together and you've got a dead short which is accepted
yeah because that way i know my leads are not damaged so if they were broken you'd have
an infinite reading yeah exactly yeah so this is all the circuits can you remind me of the
smallest amount of insulation resistance that we can get before further investigations required
so before further investigation required it can't be lower than two megaohms and that's
the whole installation it is yes okay and when we say the minimum accepted is is one
megaohm okay so you're going to first of all connect all the neutrals together and which
conductor you can do it first so i'm going to go between line and neutral at first okay
so that's on to the line connection which is on the outgoing side of the main switch
which is isolated yeah i'm just going to do it 250 volts DC first and again it's creeping
up now um it's gone way over the accepted value so it's looking around 56 57 megaohms
okay and that is on 250 though so now i'm comfortable there's nothing in circuit that
i can damage i'm going to test it at 500 volts okay brilliant DC and again that has gone
to an acceptable value um looking around 57 megaohms i do have to change this consuming
it over so i like to do these pre-tests beforehand to make sure when we're adding new devices
in especially when we go between CPC's and lines CPC's and neutrals the RCBO's we're
going to install are not going to um what conductors are going to test between next
markers so now we're going to go on to the earth bar in the consumer unit and test between
the earth bar and the line conductor we're going to keep it on 500 volts because we're
not worried about anything being in circuit now between we've already tested between the
live conductors okay so what's going to be connected to the earth bar for the insulation
resistance test something i've covered in other videos just remind me what's got to
be connected yeah so we've actually left the earthen conductor in we've left all the bonding
conductors in and all the CPC's we know that we should test our insulator resistance with
all of the protective conductors connected together to the the main distributors facility
yeah brilliant yeah okay so this is now line to the protective conductor if i just come
around and have a look okay good reading and again yeah way way above what we need it to
be again we're looking at sort of 56 57 megaohms for that i'm sure the keen eyed amongst you
have noticed the leads a bit of a mix and match remember this is the real world so we're
now between the earth bar and neutral you've left that to last any reason behind that one
well it always worries me doing earth and neutral just because especially on the old
3036 boards here um it's not going to disconnect any of the the actual fuses themselves so
if there's going to be a fault for me it's generally on this one so i like the good news
of having the high readings first or the acceptable reasons first and then the bad news if it
comes that makes sense so the customer hasn't said the fuses have been blown at any point
so if it is a neutral and earth fault it wouldn't blow a fuse and if you look straight away
we've got a dead shot 0.00 megaohms so i think our next point of call now because we've tested
it as a whole installation we're going to have to sort of break the circuits down and
try and identify which circuit if it's just one it could be multiple have this issue on
so a little bit of fault finding now you've got to identify first of all the circuit we
believe the fault is if it's one like you said yeah are we going to do that in what
way how are you going to find the circuit because it's not between a line conductor
so there's no point pulling out a breaker what you're going to have to do so i'm going
to stay connected and keep all the CPC's in together because again we know we should do
installation resistance with the more connected so i'm just going to individually take out
a neutral conductor one by one starting probably from the right hand side okay and then i'll
test the neutral bar to see if the fault was cleared and that should give me an idea whether
the um which circuit it will be okay so in practice you're taking out circuit number
one so it's gonna be the fourth one isn't it probably whichever order you do what i
always say it's always the last one you test which is the problem okay yeah if you test
it first it's not that one so this will take this neutral out and you'll go back to neutral
bar to earth and hopefully if this is the fault we'll see obviously a higher reading
on our instrument so outcomes that neutral is pretty difficult for c so there we go so
it's disconnected and neutral yeah it's terminated great isn't it okay so repeat the test now
between the earth bar and neutral bar yep and our reading is still zero point zero zero
megaohms wow so what i'm going to do quickly just while i'm here just to prove it's not
multiple circuits is test to this one and i've got a value of greater than 999 on this
circuit so i'm sort of eliminating that one from being the problem because we could find
it put that one back in and still got a dead shot so basically we know this one isn't a
problem so we can just carry on with the rest so the next circuit is a lighting circuit
and we know when we've been walking around we've seen a very old outside light we've
seen a joint box on the outside of the building as well yeah if you were a betting man would
you suggest it could be this one yeah but as you uh you've told me numerous times it's
always the last one of the fourth circuit so second number two is the lights yeah so
disconnecting the neutral i'm going to repeat the test we know the circuit that's already
out is great so we don't have to put that one back in with insulation resistance tested
on its own so by removing the lights and going back to the neutral bar we will be able to
prove whether it's that circuit or not i'm hoping it is my arms are aching now so that
neutral for the light and circuit has been disconnected yeah and we're going to test
between the earth and neutral bars so we're connected between the earth and neutral bars
and we have a reading of greater than 100 megaohms so definitely more than acceptable
and it is creeping up okay for those who don't speak screwdriver that was yeah a little bit
more than a yeah that's a that's that's a great room so yeah what's that suggestion
to you so that's suggesting to me that this lighting circuit is one with the issue we're
just going to confirm that if i just probe onto the end of that i have a dead short of
0.0 megaohms so yeah it is the lighting circuit that is causing the issue so we'll have to
do some further investigation on that circuit to sort of see what the issue is really so
before we go off looking for this lighting circuit's fault um any other considerations
to do with the insulator resistance that's when we're thinking about line circuits yeah
so naturally there's two-way switching here um so we're gonna have to operate both two-way
switches and re-perform the insulation resistance test to check the strappers in them switches
so yeah okay it's not our problem at the minute because we've got to find the fault yeah yeah
yeah that's that's the the first problem we've got to look at i'm sure somebody's going to
point it out if we don't mention it so we'll have a look at these outside lights but as
far as i'm concerned that's it for this video we've managed to find an issue we've managed
to do the installation resistance test from inside of the consumer unit doing all the
circuits at once and me and Marcus will now nip off and find the fault but as always i'm
sure we'd like to say the following what we'd like to say we hope this video has been some
help