so in this video presentation we'll look at measuring the resistance of the protective
bonding conductor this is the conductor we're simulating the domestic dwelling
that's usually size 10 millimetre squared and goes off to make connections to the metallic water pipe
and the metallic gas pipe but also can go off to the metallic oil pipe metallic structure of
a building we've got metal frame building we see it's here it's terminated within an MET
so we've got a gas which isn't present in this location it's somewhere else and one for water
often the MET is not present in installation and these connections are made within the consumer
unit itself however city and guilds and EAL always instruct us as colleges to have a separate MET
however we can't just pull out the gas bonded in this case or the water bonding those protective
bonding conductors cannot be removed with the supply still energized so let's think about why
the thinking is behind that so if i was to pull out in this case the water bond so the protective
bonding conductor to the water was taken out with the installation still live and there was an earth
fault somewhere in the installation we know from studying in the classroom that under earth fault
conditions all earth metal work becomes live so in this case metal clad socket which is earth metal
clad consumer unit etc within the installation under earth fault conditions goes live if we've
disconnected the protective bonding conductor to the water under earth fault conditions that
wouldn't go live if i was able to touch adjacent metal work so for instance the water pipe and the
metal clad socket that will clay consumer unit or some earth metal work in the installation
i would be at a differing potential no volts would appear in the disconnected water because the
protective bonding conductor would be out however the metal clad socket consumer unit etcetera
would have a voltage appearing in it we always discuss that to be up to 50 volts AC
i touch the pipe at zero volts and the metal clad socket at 50 volts difference in potential by
receiving electric shock therefore this test must be carried out with the supply isolated
i've isolated in the double pole switch or linked main switch in the tails i've expressed how to do
that in previous video presentations equally you could make the isolation within the consumer unit
itself and again i've shown that in a previous presentation supply is isolated before we start
the test we've isolated the supply here i've shown you in a previous video presentation let's get set
up now to measure the resistance of the protective bonding conductor in this insulation to a water
pipe and to a gas pipe which is elsewhere within the installation so see how we're going to do that
so i've isolated the supply in this case at the linked main switch or double pole switch
in the tails i've proved the whole installation has been isolated so i'm now able to disconnect
the protective bonding conductor from the MET which is remote from the consumer unit remember
often these protective bonding conductors will be connected within the consumer unit itself so i'm
going to disconnect the one that's labelled with a W hoping it's simulating the one for the water
the water pipe being simulated here the second one has G on it and the gas pipe is elsewhere
in the installation we'll look for that in a few moments so let's disconnect it from the MET
and now we can make a connection with our ohm meter from the disconnected protective bonding
conductor onto the front of the clamp and then onto the pipe work to prove it is continuous
we expect the reading to be less than 0.05 of an ohm which is approximately 27 meters
of 10 millimetre squared cable with simulating domestic dwelling if for some reason you're in
a domestic dwelling and your water or gas pipe etc are further away than that you'll find you'll need
to increase the size to 16 millimetres squared let's see how we're going to carry out the test
so we're also now ready to measure the continuity of the protective bonding conductor
as stated in previous presentations i've set it into the orange scale for measuring resistance
in ohms and i'm using the red and green sections within the top of the megger mft
crocodile clip onto the disconnected water protective bonding conductor
and i'm now going to take a measurement on the front of the clamp and i've got 0.01 ohms
i'm also going to make a connection onto the pipe work itself and i've got a reading of 0.02 ohms
it's all well and good proving that the protective bonding conductor makes the front of the clamp
but the earth has got to travel through the clamp and make the pipe work behind i recommend if it
is tarnished or covered in paint that we use some wire wall in order to brighten up the connection
so we can prove that the protective bonding conductor actually is earth in the metal work
and not just earth in the clamp our reading of 0.02 is less than the maximum which is 0.05
we've proved it is continuous from here one end disconnected from the MET to both the clamp and
pipe work we just need to repeat the same process now for the gas which is not in this
location therefore we need a longer wandering lead in order to get out to the gas itself
let's see how we're going to set that up before moving on to the gas i've ensured i've reconnected
my protective bonding conductor for my water i also confirmed that the clamp is secured against
the pipe as well as the cable secured within the clamp itself i can now move on to the gas
as my gas pipe is some distance away from the MET i'm going to need to use a wandering lead this is
a 20 meter long wandering lead and i will need to remove the resistance of that lead so we're going
to insert it into the machine so we're going to take one end and probe it into the machine
the other end is going to have a crocodile clip on it take a normal lead insert in the
other half and now remove the resistance of this long 20 meter wandering lead exactly the same as
we would on normal leads itself so move it onto ohms as we usually do and let's see what we get
got a read in in this case flashing less than zero i press the test button once
i have a reading of 0.69 i press it again i now have a reading of zero so what's happened now
is i've removed the resistance of what now is a 20 meter lead rather than just the normal short leads
that we have on the instrument i can now unwind my wandering lead connecting it onto one end of the
protective bonding conductor disconnected and make my connection to the clamp and to the gas pipe
let's see how we're going to do that one end of my wandering lead has been connected to the gas i've
unravelled my lead and i'm now walking down to where the other end is connected to the gas pipe
so i've come out to where the gas pipe has its connection to the protective bonding conductor
i'm going to confirm the clamp is secure and so is the conductor i've also brightened up
the pipe work to prove continuity goes from the conductor on the clamp through to the pipe and i
expect a reading no greater than 0.05 of an ohm make my connection and i've got on the
actual connection to the clamp 0.03 ohms i made my next connection onto the actual pipe work itself
and i've got a reading of 0.03 ohms the readings are below the maximum allowed which is 0.05
i've proved the continuity of the protective bonding conductor
however before i turn the installation back on i must confirm i've reconnected both the water
and gas protective bonding conductors i hope this video has been some help