so in this video presentation look at the first live test that we're going to carry out
the first live test being rechecked supply polarity so we need to prove that we've got
the correct priority within the consumer unit it could be a case that the supply authorities have
made an error in the tails or in a joint in the road and actually we've got incorrect polarity
coming into our distribution board therefore we might have for instance line and neutral around
the wrong way it's important this test is done first and that we don't go skipping off around the
installation doing her fault loop impedance tests finding then that we're not going a supply saying
the line conductor which is a simple case of a reverse polarity on the supply authority's side
stripping circuits down and start testing them so we've got to do the test in the correct sequence
our first live test is recheck polarity we're going to need to take the consuming cover off
in order to do that i'm going to isolate it at the switch within the tails 100 amp switch
within the towels so that's a double pole or linked main switch take my consumer unit off and
then re-energize it to prove the polarity of the supply we also need to take our approved voltage
indicator and our proving unit and prove that this is in good working order before we use it
if this switch is located in an outside meter cupboard or away from the distribution board
i don't recommend that we use it to turn off the distribution board at this stage problem being if
you turn it off there take off the cover obviously then you've got to go outside and turn it back on
again you've left the consumer unit with the cover off and that's not acceptable so we can do it by
turning off the main switch and this stage but i'm going to turn it off at the linked main or
double pulse which is inserted within the tails before i do the test so let's get the consuming
cover off then so before we do the test to prove the supply polarity is correct we must take our
approved voltage indicator and check it on a known supply or a proving unit the best thing to check
it on is a proving unit so i'm going to check that my approved voltage indicator is working correctly
push it firmly into both holes and we should see that all the lights in this case illuminate
therefore it's correct and working now we can go about proving the supply polarity is correct
so as i just suggested i'm going to turn off the double pole or linked main switch in the tails
but before i do that again i shouldn't turn that off on full load i should look inside
the distribution board and limit the amount of current that that switch is switching off
so in which case i'm going to turn off my circuit breakers and rcd circuit breakers and rcd circuit
breaker and then finally the main switched off and then i'm not turning this switch off on full load
so distribution board now should be isolated and i can remove the cover as i said before if this
switch is located outside you'll be turning off just simply the switch within the distribution
board so you never leave the consume unit with the cover off so i'm ready to carry out the test now
so i'm going to test first of all between line and neutral i'm going to position my
probes onto the least dangerous conductor first being the neutral and then my second probe onto
the line and remove the line first and then the neutral hopefully i'll keep myself out of the way
so you can actually see the instrument when it illuminates so let's try that so neutral first
nice and firm on and then onto the line and we can see that that is illuminated
off the line and off the neutral second test i'm going to do between the neutral and the earth bar
again going on to the least dangerous first which is the earth bar and onto the neutral and we can
see the instrument isn't illuminated and then we come off the neutral and off the earth bar
finally we're going to test between the earth bar and line again going on to the least dangerous
first which is the earth bar we're going to go on to the line and we can see it's illuminated
and take it off the line and off the earth bar with all three stages complete we can now say the
supply authority has given us the correct polarity of supply so our first live test is complete to
prove the polarity of the supply we still need to go back and prove our voltage indicator so
i'll go back in a moment and plug that into our proving unit to prove that this is correct even
though it illuminated didn't illuminate and then illuminated which for me is self-checking anyhow
once we've done that we'll be ready to obviously energize the circuits and complete the rest of the
live test in the sequence laid out by bs7671 so i'm happy the supply polarity is correct
i'm also happy it self-checked the instrument going from illuminated
and illuminated to illuminated but often the inspector will still expect you to
come back and prove your tester one final time on completion so we will here too
pushing firmly into the probes we can see once again that all the lamps illuminate
so please my students especially when they're coming out to visit you on site