- In this testing video,
we're gonna carry out the continuity of CPC
and polarity check for a radial socket circuit
wired from this distribution board here,
to six twin-socket outlets within this workshop.
In order to carry out the test,
I'm gonna use the Metrel MI 3125BT
Multifunction Tester I have here.
But why are we carrying out that continuity check?
We're trying to prove that the green and yellow conductor,
the CPC, sometimes called on-site the earth,
is continuous, in other words not broken,
from leaving the distribution board
to getting to each point in the circuit.
We're also gonna include the polarity check
at the same time.
Now you can do this visually,
I'd love your comments below
if you're the sort of person
that does a visual polarity check.
However for me, I'm going to use the instrument
and prove that all three pin positions
on the front of those socket outlets
are in the correct rotation.
So we have the earth pin,
the line and neutral connections,
and we're also gonna prove that the switch operates.
But before I can start this test,
I need to catch up and see where Rick is.
Before Rick starts that testing process,
I'm gonna take a moment just to contemplate
what we're gonna actually carry out
and think about those parallel earth paths.
- But before then,
let's have a look what today's biscuit is.
So we have here, a Fox's Fabulous Half-Coated
Milk Chocolate Cookies.
- Sounds fabulous.
- All the best.
- Before it we can undertake the test
we need to do the safe isolation procedure.
However, I don't like to turn off
distribution boards on full load current,
so I'm gonna knock off their over current protection devices
but leave the lighting circuit on in the area.
So when I find the MCB that feeds this distribution board
and when I turn it off I'll have a visual clue
that I've chosen the right MCB
'cause the lights in that area will go off.
Now we've done the safe isolation
in two free training packages,
and I'll leave a link for those in the description.
And they also go towards your annual CPD
rather than running through that full process here.
Even though I've seen the lighting circuit go off
I'm still gonna presume that this distribution board
still could be live,
so I'm gonna knock off the lights and the main switch.
So in the event of taking this cover off
and it still being live,
it will only be the terminals in the bottom
of that main switch that actually would be live
and that's the point of which you would start
to look to prove your safe isolation procedure.
Remember those links are in the description.
So once the cover is off, another top tip for you,
with those screws, especially in a college setting
is to return them back into the place
where you took them out of it
so you don't lose them in the future
and find it very difficult at the end of maybe a lesson
in order to put your consumer unit
or distribution board cover back on.
The circuit is protected by a 20 amp, type B, RCBO
with a 30 mA rating,
so you can see I delta N there, is 30 mAs
and it's also an A type RCD for this circuit.
In order to carry out the test
I'm gonna disconnect all of my conductors
from the distribution board for that radial socket circuit.
I known the onsite guide and guidance notes three
often shows a permanent link
between the line connection disconnected to the earth bar
where your CPC would be connected.
I'm gonna disconnect all of mine
in order to carry out the continuity of CPC
and polarity check on our radial socket circuit.
Next up we're gonna remove the parallel earth paths
created by the metal trunking and metal conduit
'cause for the continuity test
we wanna prove that that conductor
is continuous from the distribution board
to each of the outlets in circuit.
By removing the socket outlet,
which is also made of metal, from the trunking
we'll remove the parallel earth path of the metal trunk
in which will be earthed to the metal front of the socket.
So therefore when we carry out the test
with it disconnected off the actual trunking,
we'll be proving the conductor behind it
is continuous and not the fact that we're connected
to the trunking in front of here.
You must make sure when doing the test
also the socket doesn't touch the trunking.
Now other parts of the circuit are slightly different
because now we've got some couplers
and we've got the earth fly lead.
By removing the socket previously
we disconnected it from the earth created by the trunking.
This time we're gonna have to take the socket fronts off,
keep 'em away from the boxes during the testing process
but also disconnect the fly lead
that goes from the socket front to the socket back
in order that we can prove during the continuity test
it's the actual conductors that are continuous
and not the metal work of the trunking and conduits.
As we said, we're gonna include the clarity test
at the same time but I'm required to link
the neutral and the line conductor together
in the distribution board as part of that test.
Now we need to set up our Metrel tester.
We've got the MI 3125BT, we've powered it up
and we're ready now to put our lead in.
I'm not gonna use a set of probes
so I'm actually gonna use the plug-in lead
that comes with the tester.
So once that's in, I now need to find the actual test
I want to carry out.
Remember, we linked together line and neutral.
So we're looking at R1 plus RN,
there's R1 plus R2, which we're very familiar with.
So we need to scroll through
until we find the appropriate one.
So R2, and there we have it
and we can see we've got the R1 plus RN
and we've identified there
that we're testing between those two points.
We now need to remove the resistance of our lead,
so that means we need to bridge out the line and neutral
and I often do this using a coin.
So if I bring a coin in and bridge out
my pins for line and neutral
and then I'm gonna do a continuity test on them
to check I've connected between them
by pressing the test button.
And you see we get a reading there of 0.02 ohs
and if I press the Help button under it
you can see, Cal, this will calibrate it
and it'll remove the resistance
offered up between those two points.
So we're now ready to carry out the test
between line and neutral as part of our polarity check.
What do I like about this tester?
Well, lots of things about this tester.
However, look on the back there, there is a magnet,
and then all this metal work around me
makes it nice and easy just to put it into position
before carrying out this test between the line and neutral.
Remember, you won't be recording this reading,
it's part of the polarity check,
so as I turn it on, press the test button
I get a reading and I've got a reading of 0.08 ohms.
Operate the switch again,
as part of the polarity check you need to check
that switch does operate.
Now we're infinite or off the scale.
Onto the other side 'cause again,
the switch could have failed on this side,
we press the Test button again
and you see we get a reading considerably different,
didn't we? So, 0.02.
We operate the switch, we repeat the test.
I would suggest that's because there's maybe
a little bit of contact resistance to overcome that.
If we put the plug in and out a few times
it will clean up those connections within the socket.
Press and test again, we see a reading now
a lot closer to the 0.02 on the left hand side.
Operate the switch again just to prove it does turn it off
and we've done part of the polarity check for that socket,
we need to do all of them in circuit.
I'm not gonna show you us performing this test
at every point in the circuit
but it would be carried out at every point.
Remember, we're not recording the reading
we're just doing it as part of that polarity check.
So we're gonna do exactly the same process.
We're gonna go in, we're gonna take a reading,
we're gonna operate the switch, prove the switch works,
we're gonna see it on both sides.
Remember, you'd expect a very similar reading on both sides,
which we didn't get at the first socket outlet.
And then we are gonna go all the way now
I'm gonna show the last point.
So our readings are hopefully are getting higher
from the first one to the next one we test.
And now this is the last one
and we've got a reading there of 0.12 of an ohm.
We're checking that switch
and we'll check the other side as well.
So this is the last point on the radial circuit,
we know that 'cause there's only one line,
neutral and circuit protective conductor
in the back of the actual outlet itself
but that reading is not recorded
it's just part of the polarity check.
In order to complete the polarity of the socket outlet
I need to test now between line and CPC,
this will also generate my R1 plus R2 value
which I'll record in my test paperwork
under the box heading, Continuity.
We now need to set up Metrel MFT tester
in order to do the R1 plus R2 test
so we scroll through until we find it.
Again, we're gonna remove the resistance of the leads.
We've positioned a coin across
the appropriate pins in the plug,
we've pressed it, we've got 0.1 of an ohm,
we've pressed the calibration button,
it will remove the resistance of the lead
and we're ready therefore to carry out that R1 plus R2 test.
And you know it's on the screen,
it also shows us that we're measuring
between the line and the protective earth during this test.
Again, we're gonna start with the closest socket
to the distribution board
and we expect the readings to increase
as we move further away.
So first one is 0.03
when we're measuring between the line and the CPC.
Remember, it's disconnected from the trunking
which was a parallel earth path
and we're gonna do both sides of the socket outlet as well
'cause we need to prove that that switch will operate.
And then once we've finished the test
we do need to leave both the switches in the on position
for a test we're gonna carry out in a different video.
We continue this test on all the socket outlets
on the circuit,
remember, we're looking for the highest reading we achieve
to be recorded as our R1 plus R2 value.
We had 0.06 ohms there
because we are further away from the distribution board
therefore there is more circuit cable
and it's that circuit cable that is offering resistance,
so we expect to get our highest reading
at the furthest point of a radial circuit.
We've now worked our way to the furthest point
in a radial circuit where we expect
to get the highest reading
'cause it's the longest amount of cable
to get to that point.
However, whichever reading was the highest
would be the one that you record.
And we operate in a switch,
we're doing that polarity check.
Remember, polarity is proving the positions of those pins
by testing between the line and neutral first
and then the line and CPC second.
We've proved that all three pin positions
must be correct by proving two of three,
you actually prove all three are in the right place.
So we can now record our reading for our R1 plus R2 value,
R1 being the resistance of the line conductor,
which we measured added to the resistance of the circuit
protective conductor, which was R2 as 0.13 of an ohm
in the appropriate box in our test paperwork.
We can also tick the polarity box,
we did it through measurement, didn't we?
In order that we proved the three pin positions
were line, neutral and the protective conductor.
Remember, if you do it visually,
you must look at both the cable colors,
two browns and two blues but also the L and N
in the accessory to prove visually polarity is correct.
Just the case now getting the fly leads reconnected
and the covers back on.
Be really interested in your thoughts and comments,
do you use fly leads when you've got two fixed lugs
in electrical accessories?
Please make sure you leave those comments below as well.
- You're just saying, I did this and I did that a lot.
- Yeah, I did, didn't I? - Oh in fact,
I think I did it all, didn't I?
- We'll you did most of it.
- I'm gonna go get some biscuits.
- While Rick goes off to choose the biscuits
that we're gonna have in our next video,
a little tease for that
as I look inside the distribution board
I can see all three conductors are disconnected
on this radial socket circuit.
However, one of them needs to be connected
in order that we can carry out
the insulation resistance test.
And if you wanna find out what that is
check out the video on screen just there.