a distribution board or maybe called a fuse box for those people in their early stages of study
so we're gonna have a look at the basic principles of what the main switch is doing the overcurrent
protection and the earth fault protection is doing within the distribution board itself so we go to
the mains end position in any domestic dwelling and we find the consumer unit in this case this is
a 17th edition amendment 3 distribution board and is made completely of metal it also has a lid that
closes down so it falls into a closed position as we look at the outside of it I believe at least
one sticker is missing we haven't got the one for the periodic inspection so telling me the
date of when it was inspected and the data when it should be re inspected and I'll find one of
those in a moment a domestic dwelling requires re inspecting no greater than 10 years between
the inspections we have got one sticker on the consumer unit front this is the one telling the
customer you need to test their RCD by pressing the test button seeing it go from the on position
to the off and reset it that should be carried out quarterly or every three months something
that's often missed in domestic dwellings that customers don't go to their consumer unit and an
test quarterly their RCD when we open up the flap we can see some of our over current protection
devices our RCCB and our main switch so let's have a look at the functions of those them so
every distribution board or consumer unit or fuse box so everyone would like to call it's called a
distribution board should have means of isolation in this case on the right hand side for me we've
got the double pole or linked main switch this can appear on the other side depending on the
design of the consumer unit and this switch here can be used for two purposes it can be use for
mechanical maintenance so we can isolate and work on the electrical system or it can be used as an
emergency isolation for mechanical maintenance I would expect us to turn off the overcurrent
protection devices within the installation and then turn off offload the main switch and we
can see now it's gone to green at the top green to suggest it is off and when we're in the on
position that switch blades are red at the top so for danger so if we're going to use this from the
maintenance I expect the distribution board to be isolated and the main switch to be turned off load
however the same switch can be used for emergency isolation so in other words we can use as a onload
isolating switch so the installation is completely on and for some reason the electrical current
needs to be turned off in a rush so you can turn it off on full load as an emergency isolation
switch as well this is double pole it will turn off both live conductors both live conductors
being line and neutral and it turns them off simultaneously so together it will turn off both
line and neutral this is often called a double pole switch but also in the regulations can be
called a linked main switch or distribution boards need to offer over current and short-circuit
protection and that's in the form of a fuse in this case that has been offered by a circuit
breaker and we've got circuit breakers throughout the distribution board here so they're offering
overcurrent in other words you have a healthy circuit saying this one rated the first one of 20
amps a healthy circuit rate of 20 amps is asked to draw say 30 amps over a period of time then
we expect over a period of time that overcurrent protection device to operate that will not operate
necessarily within the maximum given time for an overload in other words circuits up to including
32 amps must currently under the 17th edition wiring regulations disconnect within point four
of a second but for an overload fault this could be many minutes or many hours before operation
occurs this will be explained in the classroom when we look at fusing factors the amount of
current required to operate a device so it might be rated the first device at 20 amps that doesn't
mean it will operate when he gets over 20 amps so for overload the disconnection time in this case
of point 4 is not applicable the disconnection times are applicable when we look at short circuit
in other words line and neutral have come together or a live conductor and Earth have come together
causing rapid disconnection of the supply so it may have a fault of a negligible impedance in
circuit and we expect that huge fault current to be cleared very quickly and as we just said the
first device being rated at 20 amps under those conditions would disconnect in point for a second
or less as we move down we've got a 32 6 32 and a 20 these are all type B circuit breakers these
are used in domestic dwelling where there are few surging loads so we haven't got many loads that
can draw massive inrush currents when we move into industry and looking distribution boards we often
see C type boards sorry C type breakers within the distribution board or d type so where we
have huge in rush currents on things like welding equipment and some air conditioning units you may
have a D type breaker and where you have lots of 4 fluorescent lighting circuits been switched
on in one go you tend to have C type breakers and again will cover that in the classroom so as well
as having the linked main switch and overcurrent and short-circuit protection offered by circuit
breakers this distribution board as many do now in industry have residual-current devices in two
positions here protecting the outgoing for neural circuits these RCD's are rated at 30 milliamps or
less and offer additional protection we will go through additional protection in the classroom
and we have done in some of my other video presentations the RCD will clear earth faults
so a live conductor either line or neutral to earth fault will cause the RCD to operate and
if we press the test button we can see that the RCD will trip into the off position and require
once the fault has been cleared we energizing ok pushing back to the on position we can have
circuits that aren't additionally protected as we have here with a sub main circuit we'll go into
that into the classroom how we can get around some circuits not being additionally protected
by an RCD but generally is in industry you will have either RCBO's or our RCCB's protecting the
circuits within a domestic dwelling so we've got several circuits this side of the RCD and several
circuits on this side of the RCD even we split them across more than one so we've got two in this
case RCCB's is that we can have discrimination so in other words if one side was to trip off
where on earth fault will only lose 50% in this case of the installation and best practice is to
split light in circuits and socket circuits oppositely over the actual to RCCB's so the
word if we had the downstairs sockets and upstairs lights this side would have the downstairs lights
to an upstairs sockets on this side so in the event of losing one half of the installation you
still may have residual light offered by TVs and table lamps if you've lost the lights as you're
obviously therefore working your way down to the consumer unit or to wherever it is positioned
in order to reset the RCD often consumers can be fooled by the fact they believe their circuits are
energized but they have no power to things such as lights TVs and cookers because when they get here
all their circuit breakers are in the up and on position but what it has potentially happened is
that maybe one of the RCCB's is tripped out with an earth fault and they've come along and looked
to see that the breakers are all up and they're now wondering why half their installation has
no electricity this is where electrician can be called and comes out and simply clears the
earth fault and resets the RCCB and the circuit therefore re-energizes so just be careful when
you're out there in industry that we look not just at the circuit breakers if there's been a
fault and one of those is potentially tripped off it's easy to see that that circuit therefore is
only off when more than one circuit has gone off the chances are that one of your RCDs is operated
causing potentially half the installation to go off simply clear the earth fault whatever caused
the issue before resetting the RCD likewise when we have a fault on a circuit breaker that's caused
it to trip into the off position we must clear the fault first before we re energize the circuit
breaker itself we don't clear the fault it won't allow it to reset it will keep tripping back out
all the overcurrent protection devices in this installation are B type circuit breakers domestic
dwellings have B type circuit breakers where there is few surging currents in a domestic dwelling
however as we move into industry you may see C types perhaps where there's a lot of fluorescent
Lighting being turned on and D types where there's large compressor units air-conditioning units or
welding equipment where there's huge in rush currents when the item is turned on again we'll
cover that in another presentation on overcurrent protection devices and in the classroom but these
are all B types of B 20 B 32 B 6 B 32 and a B 20 often we see the correct sized fuse and sticker
here suggesting what it is so we've got a socket circuit here picture and we've got a B 32 so we're
thinking that's an A1 ring final circuit I've got a picture of a light here and a B 6 and that
suggests obviously it's a lighting circuit moving down here we've got a picture of a a cooker and
a B 32 so that makes sense as well and then the final one is a socket but this time it's a B 20
perhaps adjusting that's an A3 radial circuit our sub main garage feed is in on a B 20 so we've got
B C's and D type breakers and we need to look in a domestic dwelling that they are all B types we
wouldn't want them all to be D or C types and we will go into that into the classroom so I'm gonna
have a look inside this distribution board and we cannot take the cover off with it's still in
the on position and as we said before if this is for maintenance purposes we should turn off the
overcurrent protection devices or we could have turned off the RCCB's and then we're going to
actually turn off the main switch so we're now in the off position and we're gonna do these
screws fortunately in this installation I've also got a link to main switch in the tails so I could
have isolated there they're not as common as they should be so for this installation and for this
video I've just turned off the main switch after turning off the overcurrent protection devices
and now I'm gonna take the consumer unit front off so we can see the consumer unit cover is now
off so our main switches off we're taking off the consumer unit cover and we're potentially
looking to prove isolation before we work in here so we've proven at the bottom of the main switch
that the board is isolated before doing any work and I'll show that in another presentation how to
secure isolation and prove the bottom of the main switch is isolated I've done that off-camera and
now we're looking at the basic layout within a consumer unit in this case a split board so
we've got in this case three neutral bars okay we've got one for the dedicated circuit that is
not on the RCD which is our sub main circuit going off to a garage in steel wire armored cables got
an earth metallic sheath and doesn't require RCD protecting and then we've got the two our RCDs
neutral bars so you can be careful to make sure you what what which neutral follows on to which
bar when positioning the line conductors this side with the appropriate neutral from the RCD
of which you've got the line from so then equally this side the line bar here at the bottom okay is
for this board and then we come across this RCD here I don't like the fact that we've left these
bare have left and bear for this presentation to show you what happens in industry we have
no IP rating protection all these well we have everywhere else I cannot touch any of the live
parts here or here but I can touch them on the top of that bus bar which is not good practice
they should be insulated with a little plastic seal over the top which I showed in one of our
previous presentations I've shown it like this because this is often what we see in industry
about the bar should been cut off all together so it's only been used for the circuit breakers that
side of the RCD and that side of the RCD so we'd get rid of the problem that way it's imperative
that you get the appropriate neutral from our RCDs and lines into the appropriate neutrals
here in the event of you having a neutral in the wrong side of the RCD you create an out
of balance which will cause you when you go to energize the circuit for the RCD just to keep
dropping out we have only one earth bar of which they all go into so we've terminated not only the
the main earthing conductor but also the circuit protective conductors into that earth bar we can
also see in this installation how we've identified L&N on the tails as well as number identification
on the conductors or such as your neutrals and CPCs and the event of me wanting to disconnect
the circuit focus to pull out line conductor three I'm looking for neutral three and CPC
three in order to remove that circuit from the distribution board and then take it out perhaps
it's being replaced or removed so to recap them linked main switch double pole can be used for
maintenance or emergency we prefer to turn this switch off with no loading circuit it turns off
both line and neutral simultaneously or together and we can see those two conductors coming to the
top of it we cannot touch any other live parts therefore even inside the consumer unit we've
got IP2X however we fail here for IP2X on both sides because we haven't cut or insulated the
rest of the busbar we identify the conductors with tags such as L and and then number identification
for each individual circuit in the event of you needing to remove a circuit we should be
able to see the number on the tag on the line conductor same on the neutral and same on the
circuit protective conductor in order to remove it so that concludes some of the basic principles of
what's happening within our distribution board consumer unit or fuse box whatever we are going
to call it this stage looking at isolation overcome protection and a fault protection
remember you can follow my group on Facebook if you want if you look into the description of any
of my videos you'll see a link to my Facebook page and you can see what's going on within my
classroom and some of the things I post on there to help them hope this video has been some help