why ed from pegasus electrical's just making those final connections to liven up our schneider
acti 9 isobar p distribution board i thought i'd jump in and do the external earth
fault loop impedance of a three-phase supply now this might be something that's very useful for
apprentice electricians doing am2 am2s or am2e and also it's got a slightly different met main earthing
terminal so we get a chance to have a look at that as well so we can do some testing with ed
if this is going to help with am2 obviously we're going to have to have a look at the
arrangement we've got here we're going to carry out that external fault loop impedance test but
we've actually got the main switch here four poles switch for our three-phase distribution board but
in our system we've also got an external isolating switch where we're going to carry out our test
if for some reason you don't have one of these at your am2 am2s ram 2e assessment everything
we do down here would actually be carried out at the bottom of this switch here which you can see
is in the off position for your am2 obviously we're going to have to isolate the distribution
board before starting the test and we're going to do it from the bottom of the switch or in
our case from this switch over here because we're going to remove the earthing conductor
obviously the installation will have no connection to earth therefore ads wouldn't be in place so
all of the devices within the distribution board have been isolated we've isolated down here and
it could be that the bottom of the switch is live for testing purposes but on ours we're going to
test it down here in order we can carry out that external fault loop impedance test so that's the
first maybe subtle difference between yours and your am2 rig and the other thing i want to show
you down here is our main earth in terminal which you're likely to have at your am2 but we're going
to disconnect in a slightly different way so we're going to bring eddie and we'll talk about removing
those parallel earth paths can you just set your instrument up for us and then we'll go through the
test and we'll talk through what we're going to be doing eddie so what you're going to set it to
for me i'll reset it to the zed z4 what that's for the impedance okay so we're carrying out a
live test we're measuring the external impedance offered by the supply authority's cable feeding
the installation this earthing arrangement can you just remind me what it is this is a tncs
and what's the maximum z-e available for a tnc s 0.35 of an home that's right so we'd
expect this reading to be considerably less than that of course but that is the maximum however
we've got all these parallel earth paths here one of these green and yellow conductors coming out
and up is actually for the board itself so that's the earthing conductor coming in just there
the other one however goes off to something else what does that go off to that goes up
to the structure of steering of the building which is buried to the greater mass of earth
so that becomes a parallel earth path so all parallel earth paths need to be removed
on am2 m2s and m2e that might be the case that you've got a couple of green and yellow conductors
going off to maybe the gas and water so in order to remove those parallel earth parts we normally
just take out the conductor which is there which is our earthing conductor from the met but with
this system we don't have to do we what are we going to do in order to remove that parallel path
on this system gary we've got a link which we can remove okay so when we take that out
effectively the installation has no connection to earth well we've turned everything off up there
and we've removed the parallel earth path in this case created by the structural steel work because
there is no bonding to water here because it's got a plastic incoming water pipe so that's now
got the external earth source we could connect to there and the bottom of our switch in order
to do the test and that's probably what you might do on am 2 am2s and n2e but we're going to connect
between our disconnected earthen conductor and our lines of the three readings we get now eddie which
one will we record we'll be recording the highest one gallery okay so you're going to probe one in
the safest possible manner so i'll take it we're going to clip onto our earthing conductor first
we're currently off because obviously the isolating switch is off
so earthing conductor and then our machine needs to be turned on yes on this meter we go to
lpa first for the lighter earth so that's line to protective earth
and you're going to measure between l1 first uh yes we will go yeah okay so l1
you need to have it on well we knew it was off so that's good so we've got a voltage
you've got it set to three lead low oh yes we have here okay so there's your first one
so we're going to connect it to you're going to go two lead high yep the reason we can do a high test
is because there is no rcds is there no okay so again i don't know on your am2 and 2s and
m2 e rig whether there is a an rcd but your instructor will tell you so we're two lead high
right so that's considerably less than the maximum just remind what the maximum was 0.35 so that says
finish the test agreed yes oh we've got to do the other two lines do the other two lines now
okay so we don't we can't just take that first reading we've got to do all three so this is l2
okay and of all the readings you get which one we record eddie we'll be recording the highest
one okay i know some people record all three but the paperwork will require the highest one to be
recorded so is that the highest one that's the lowest one okay so 0.22 we'll be recording for
this so that's the external earth fault loop impedance the z e of the installation agreed
correct so it's not a ze test it's the external fault loop impedance that we just measured we know
the earthing arrangement is tncs and we know the maximum was 0.35 and we got it under the maximum
we're going to record the highest of the three readings that we got you happy with that test
yes