so carrying on from the last video where we was talking about earth fault loop impedance and
three lead low two lead high and two lead low um we obviously seen a measurement of
3 lead low and two lead low we couldn't do the two lead high however because we know now that
that will actually cause an RCBO or an RCD to disconnect so this video is following on from
that and basically we're going to now use the two lead high setting okay which i've got on
my tester here as you can see it's set to the L-PE and the impedance values on the tester
and is set to two lead heights what we are going do now is we're actually going to measure
our external earth fault loop impedance our Ze now because there isn't an RCD down
circuit um because this effectively coming straight into the the income out et cetera
it shouldn't cause an issue and we should be able to get a reading okay so i'm gonna connect onto
my earthing conductor which you notice i've actually disconnected so the whole idea is
we actually want to make sure that the earthing conductor and the supply authorities means of
earth in there provided us is actually what is giving us our path to earth okay so if i would
have left it connected maybe there might have been a gas pipe water pipe etcetera if that other thing
conductor was broken we actually left it connected into the MET in this skeleton board here okay
then we might actually get an acceptable reading however that could actually mean that affectively
we're using our incoming services such as gas and water as our means of earthing which would not be
a good idea okay so i've actually disconnected it notice that the whole board is turned off okay now
again disconnected our earthing conductor so this is our means of earthing into the installation
if something if i was to leave this live and then there was a problem let's say the metal face plate
then that could cause issues and danger to the customer or people in the area okay so because
i've disconnected the earthing conductor i've obviously now turned the whole installation off
okay so onto the earthen conductor and then i'm just going to come on to my incoming line
and that has given me a reading again as you can see quite a lot quicker than when we did the three
lead low of 0.23 ohms okay now what we're going to do is we're going to follow on while we're doing
the this test we're actually going to perform our perspective fault current so now we're moving on
to our perspective fault current again and as before we can carry on from this when we're
doing our external fault loop impedance the only difference now is i've reconnected the earthen
conductor into the MET and the board and this is to make sure all parallel earth paths are in place
okay so what i'm going to do is i've connected to the MET i'm just going to go on the incoming line
conductor and it gives me the voltage and then rather than looking at the the impedance value
now we're actually focusing on the number above it which has given me 799 amps so that is actually
my perspective earth fault current okay the test isn't quite finished there we need to then do our
prospective short circuit current and whichever one is the highest will actually become our Ipf
or our prospective fault current as such and then we can have a look at the braking capacity on the
side of our overcurrent protective devices and make sure they are adequate for the installation
so now we've done our prospective earth fault current we're going to move on to our perspective
short circuit current as we spoke about now this is between line and neutral so i've got the tester
here set to line and neutral loop and in the back all i've had to do is swap the test lead terminal
from the protective earth to the neutral terminal so all i'm going to do is probe onto the incoming
neutral and incoming line terminals it's going to give me the voltage on the two lead high and then
you can see the results so we don't actually need to massively worry about this okay we just need to
focus on the perspective short circuit current it's given us which is 759 amps so now we have
to look at the two okay the perspective earth fault current and the perspective short circuit
current whichever is the highest actually becomes our perspective fault current now we then need to
check them on the side of our overcurrent protective devices in this installation
the overcurrent protection devices are rated at 6000 amps okay so they're acceptable so the
braking capacity must on the side of the devices we have must be higher than our prospective fault
current okay which they are in this installation as always we hope this video has been some help