different installation and as before we need to work out the earthing arrangement this one
has its origin so we're going to go and find the metering position this time is an outside there
is no meter cupboard this time so we're gonna have to go and investigate where the meter is
and the consumer unit and see if we can work out which earthing arrangement we have this
time so this time we're under the stairs with the mains intake position okay and we're going
to look and see which earthing arrangement we have this time could be the same as our last
video at our last video we identified a TN-C-S earthing arrangement we're gonna have a look and
see what we've got this time so as before we've got a kilowatt hour meter we've got our cutout
section here including our cutout fuse which this time is rated at 60 amps remember it can
either be rated at sixty eighty or hundred amps for a single phase domestic dwelling we've got
our tails attached to our consumer unit here as before sized at twenty five millimeters
squared and our earthing conductor is sized at sixteen millimeter squared please know in this
installation the supplier authorities side of the meter the tails are sixteen millimeter squared
and not twenty five millimeters squared this installation unlike the previous one we looked
at for the TN-C-S earthing arrangement has no double pole switch inserted in the tails so in
these tails here we cannot isolate the consumer unit itself isolation for the distribution
board has to occur within the distribution board itself so in the event of you required to change
the distribution board you would need to pull out the in this case the 60 amp fuse which is
sealed by the supply authorities and you would require permission before breaking those seals
so to work out the earthing arrangement we have this time we look at the supplier for its cable
incoming into the bottom of the cutout which is here we can see it's considerably larger in size
physical size that is than the one we had on our previous earthing arrangement and we can quickly
identify here this braided section of the sheath of the incoming supply cable then terminate into
our MET our main earthing terminal and those off in a 16 mil earthing conductor to our consumer
unit so we've got a slightly different arrangement here we haven't got it coming out of our cutout
as we did on our TN-C-S earthing arrangement where the earthing conductor and neutral were
together within the cutout with actually got it separated off the sheath of the incoming supply
cable we see the connection from the sheath of the incoming supply cable has been labeled with
safety electrical connection do not remove if this was to be disconnected from the installation the
whole installation would lose its incoming earth so we are look at the supply Authority's cable
incoming to work out the earthing arrangement we've got we can see this time we have this
steel outer sheath being taken from the outside of the supply Authority's cable into the MET the
main earthing terminal and not in our previous earthing arrangement TN-C-S coming out the same
termination point as the neutral so therefore this earthing arrangement must be different than
the one we previously looked at in our video so we're now looking at a earthing arrangement where
it comes off the outer sheath of the supply Authority's cable so we're looking at a TN at
terror neutral and then S for separate in other words the supply authorities will bring in a line
conductor a neutral conductor and a separate earthing conductor into the installation two
common materials used for this separate earthing conductor coming into this installation are either
lead of the sheath of the cable or steel of the sheath of the cable in this instance were coming
off with a connection to a steel sheath cable if it was a lead sheet cable care must be taken
to check the clamp around the lead is correct sometimes they turn use bonding clamps which
works really like holding putty or playdough the more you squeezes the more the lead will move away
and be less tight you normally have to sweat on to a lead sheath cable in order to connect your
earthing conductor so to recap then the supply authorities are brought in a cable containing
three conductors line in neutral conductors terminating within our cutout separated for
a neutral and the line going through in this case the 60 amp incoming fuse we're using the outside
sheath of the cable to provide us with our earth connection okay so goes into our MET and then
goes out into our 60 mil earthing conductor the incoming supply Authority's cable often had lead
or steal sheath for that protective conductor in this case we're connecting to one which is made of
steel we see later on in our learning at college that the TN-S the terror neutral the earth and
neutral a separate TN-S earthing arrangement has a maximum external earth volt loop impedance of 0.8