so in this presentation we look at the requirements for ADS automatic disconnection
of supply it is not acceptable to have a fault in circuit that remains there for an extended period
of time as there is a rise of risk of electric shock fire and explosions in the event of a
fault we expect the circuit with the fault in it to automatically disconnect leaving all of
the circuits are healthy obviously energized and still working in order for this to happen
ADS has to be in place and we're going to look at the requirements for ADS on this rig this
really simulated an earthing arrangement which is TN-C-S and we're going to look at the conductors
and how they are connected in order to comply with a ADS we will also add in the IP ratings
of electrical enclosures and talk about expose the extraneous parts in order for ADS to apply
we're going to look at the mains end so we've simulated here our mains end and we've got our
double insulated meter tails coming in from our cutout I've cut out in this case there's
a hundred amp fuse in it that could be 60 or 80 so the supply authorities have provided us
this time with a hundred amp single-phase cut out the 25 millimetre square tails are in place is a
TN-C-S earthing arrangements of the tails are 25 millimetre a coming in from the supply authority
and the double insulated meter tails coming out from the meter are also 25 millimetre squared an
entire consumer unit we have the green and yellow conductor from the supply authority this one here
is the earthing conductor and is 16 millimetre squared the 16 mm2 when earthing conductor goes
into in this case our main earth terminal MET some installations don't have an MET and the 16 mm2
earthing conductor would come from the supply of authorities directly into our consumer unit earth
in this instance and a lot of awarding bodies such as City and Guilds and EAL would love to
have an external MET main earth terminal so our 16 mm earthing conductor comes in is terminated into
our main earthing terminal we go out into our consumer unit again with an earthing conductor
size 16 millimetre square so this conductor for all intents and purposes the same conductor is an
earthing conductor in this installation from the MET we've got our protective bonding conductors
which would go off around the installation to connect to gas water and oil in this case we've
simulated termination at a metallic water pipe and a metallic gas pipe the protective bonding
conductors are 10 millimetre squared in size as a rule of thumb in a domestic dwelling this one
likely never to be bigger than 10 millimetre squared and we size it off our incoming tails
that it's worth bearing in mind if in a domestic dwelling the gas water oil etc is more than 27
meters away from the this case main earthing terminal needs to be increased in size very
few domestic dwellings would have a water gas or oil pipe considerably a long distance away such
as greater than 27 meters our default position at college is that we have obviously 25 millimetres
squared double insulated meter tails and domestic dwelling our earthing conductor is 16 millimetres
squared and I'm protecting bonding conductor is 10 millimetres squared as we move into industry and
the income in supply cable is far greater these conductors increased dramatically in size this
is a hundred amp domestic dwelling that we're simulating to our conductor sizes up 25 16 and
10 millimetres squared the protective bonding conductors in this case we're simulating going
to gas and water are terminated is difficult to see on here they have to be terminated with
the clamp that says on their safety electrical connection do not remove has to be terminated
within 600 millimetres of the incoming point so in other words consumers side after a water
stop tap after the gas meter within 600 mm of entering that installation however if there is
a tee piece and they call it a branch in the Regulations if there is a tee piece in either
gas or water pipe the clamp must be made before that if it is obviously under six hundred mm so
it's within 600 mm or before the first branch in order that we make these two connections or oil
obviously same principle applies so protective bonding conductor a 10 millimetre square goes
often connects to a gas and water pipes which are metallic in this case within 600 mil consumers
side in the installation in the event of them in a fault to the metallic water pipe or metallic gas
pipe we expect the circuit to disconnect we do not expect the voltage between bonded metalwork
to rise above 50 volts AC we expect automatic disconnection to occur as we rise up to that 50
volt value 50 volts is the touch voltage AC the point of which he starts to feel as a human being
starts become uncomfortable we wouldn't want to voltage to appear in our pipe work so therefore
once we are approaching that value we expect the circuit to automatically disconnect what we
also wouldn't want to do is if we had adjacent pipe were next to each other one of them being
at zero volts potential and one of them being at say 30 or 40 volts potential if the pipe work was
close enough together you create is a arc between the two pipe works and that arc if it was coming
from the water pipe to the gas pipe could burn or mark away at the pipe causing it to eventually to
rupture obviously the arc would then create a fire and also an explosion against the gas so
remember ADS is trying to reduce the risk of three things shock fire and explosions so we bond our
metal pipe work in order to we keep at the same potential we wouldn't want that potential to rise
above 50 volts AC so let's clarify that if this point here had a voltage in it say up to 50 volts
and this pipe here was at zero volts potential and they were a very close together there is a
great chance that the voltage that appears here in the water pipe would make its way jump across
through an arc onto the gas pipe eventually that art could burn its way through the copper and then
eventually ignite the gas within it so therefore not only when there's a voltage appears in the
pipe there's a risk of electric shock if we could write an arc you know I can cause a fire and if
the arc goes to something that's highly flammable but it is gas it burns its way through officers a
massive risk of explosions so in order to reduce the risk of shock fire and explosions we must make
sure that all bonded metalwork is at the same potential in order for ADS to apply we need
the appropriate fuses in the appropriate places we've already suggested that the fuse here in
the incoming cut out a hundred amps it could be 80 or it could be 60 we've got a hundred don't
cutout fuse 25 mm tails 16 mm earthing conductor entering our consumer unit before entering our
consumer unit I want to confirm the IP rating IP stands for index of protection or international
protection both of those can come up in our exam both for IP and what it stands for so we want the
IP rating of this electrical enclosure and all electrical enclosures to follow the following
rules the top surface of any electrical enclosure consumer unit cooker switch socket outlet it
must be IP4X in other words objects exceeding 1 millimetres cannot enter the top of any electrical
enclosure what we're trying to do is prevent dust fall into the top of an electrical enclosure and
then building up so the IP rating at the top of all electrical enclosures must be might be IP4X
the remainder so the sides and bottom and sides and bottom of an electric enclosure must be IP2X
objects exceeding 12 millimetres cannot enter that electrical enclosure what it's really suggesting
for IP2X is that we cannot stick our index finger into the electrical enclosure includes the front
surface as well so as we open up our consumer unit we can see that the blanks are in place meaning
that I cannot push my finger into any part of this in electrical enclosure meaning the front surface
also is IP2X will expand this knowledge as we move forward and we start calling IPXXB or distinguish
the length of the finger and the width to be 80 mm long and 12 mm wide that can also not enter the
electric enclosure but a time being where we are on our studies I just remember that IP index of
protection or international protection top surface is IP4X objects exceeding one mm diameter and I'll
enter the sides bottom and front our IP2X so in order we apply to ADS all the circuits within the
installation must also automatically disconnect in the event of a fault so when we open up our
consumer unit we can see we've got individual overcurrent protection devices in this case in
the form of circuit breakers the main switch hear is a linked main switch or a double pole switch
will simultaneously turn off both live conductors when we operate the main switch it will turn off
both the line and neutral simultaneously at the same time to isolate the distribution board our
individual overcurrent protection devices go off to feed cooker sockets lights and that the
installation and need to be sized correctly often the a lighting circuit is fused at 6 amps a ring
final circuit of 32 a cooker circular 32 these overcurrent protection devices also have maximum
disconnection times in the event of a fault the rule currently is circuits up to including 32 amps
must disconnect within 0.4 of a second circuits over 32 amps have a maximum disconnection time
of 5 seconds so we've looked at the earthing conductor a protective bonding conductor also
remember part of the earth family for ADS will be the individual circuit protective conductors cpc's
that will go around the circuit to each individual accessory so they've got the CPC's in place as
well so in the event that they've been a fault in the circuit potentially the CPC could become live
another to disconnect the circuit and we expect or disconnection times to fall within either 0.4
or 5 seconds depending on the size of the actual device itself as we look at our lighting circuit
we can see that our switches and in this case battery lamp holders are all insulated so they're
all plastic so in this case of CPC is actually connected within they're not serving any purpose
moment so I've got a CPC connect in hidden here but it's not serving any purpose however this
can be changed or the switch can be changed for a metal one that is an exposed conductive part
all exposed conductive parts need connecting to the CPC in the event of an exposed conductive
part becoming live we expect the circuit to automatically disconnect in order to reduce
the three things I stated earlier shock fire and explosions so there is a CPC inside the switch
as a CPC inside my batten lamp holder they're waiting for the fact that it could be changed
for an exposed conductive part the socket outlet on this part of the circuit is metallic so they
are exposed conductive parts so as well as being terminated into the actual termination in the
socket outlet back so the pin here at the front can be an earth pin that also is earthing the back
box and the front plate because these are exposed conductive parts in the event of this socket
outlet becoming live it would be unreasonable for somebody to walk up and touch it receive electric
shock we expect the circuit to automatically disconnect before that happens under ADS it would
so the event of this exposure to conductive part becoming live it would automatically disconnect
the overcurrent protection device within the consumer unit within the specified time or
a socket circuits on ring final circuit fused at 32 amps then we'll disconnect within a maximum of
0.4 seconds in order to reduce the risk of three things shock fire and explosions so with ADS in
place in other words we've got the appropriate sized fuse coming in of the incoming point and
appropriate size fuses within the consumer unit we've got our earthing conductor in place and
sized correctly our protective bonding conductors if required off to a gas water or oil etc and
we've got our circuit protective conductor coming around most of ADS now is in place however we can
use additional protection on top of that so ADS is in place but we can additionally protect the
circuits and that's commonplace now in domestic dwellings is that additional protection will be
offered by an RCD a residual current device rated at 30 milliamps or less so we can see inside of a
consumer unit that we have an RCD here and an RCD here and that's a split board so this RCD here
rated 30 milliamps protects a number of circuits going this way and this RCD here protects a number
of circuits going that way so they have additional protection the RCD rated at 30 milliamps offers
additional protection additional protection is required for socket outlets so these socket
outlets are rated up to 20 amps these are 13 amp socket outlets and currently in the regulations it
says all circuits up to 20 amps of socket outlets require additional protection this may be tweaked
as we go towards the 18th and looking at socket outlets up to 32 amps it isn't the rated value
of the breaker for this ring final circuit may be rated at 32 amps if the rated value of the socket
outlet itself these are 13 amp socket outlets and socket outlets currently in the 17th edition up
to 20 amps require additional protection but again look out for it to go possibly
up to 32 as we move towards the 18th edition so all socket outlets in a domestic dwelling
are going to require additional protection by an RCD rated at 30 milliamps other additional
protection will be required where cables are running stud walls so again if you've got
lighting circuits cooker circuits etc all running stud walls with no further protection additional
protection would be required if you're not burying cables in the wall at a depth of 50 mm or greater
those circuits will need additional protection you can't get round additional protection by an RCD by
installing cable systems in a domestic dwellings such as steel wire armored mineral insulated FP
200 fire tuff in other words a wiring system with a metallic earth sheath that would mean that all
circuits would need to be wired like that rather than put in an additional protection via an RCD
industry is deemed is easier to additionally protect all circuits in a domestic dwelling on
a RCD rate of 30 milliamps or less rather than trying it round that in some instances we can't
get around it socket outlets we can't they have to be additionally protected by an RCD because
the socket outlet can be plugged inside and then the taken outside so therefore all sockets need
additional protection by an RCD also or circuits in a bathroom need additionally protected by an
RCD rate of 30 milliamps or less doesn't leave many circuits left in the house where we would
for instance wire in steel wire armoured prevent additional protection or bury those cables 50 mm
or greater in a wall the reason being we don't want someone to inadvertently screw into nail
into cables that are buried in the wall creating a fault so to overcome that we all have to have
an earth metal sheath such as a steel wired armoured or an MI cable would provide buried
at 50 mm deep so we believe that they wouldn't be damaged inadvertently by somebody hanging
that picture on the wall and hammer a nail in industry doesn't going down that route industry
goes down the route domestically of additional protection for all circuits offered by an RCD
rate of 30 milliamps or below in order to achieve discrimination between our RCDs we're going to
have more than one okay what we don't want is an RCD protecting all ten circuits in a domestic
dwelling and the event of there being an earth fault in there then we disconnect all ten circuits
in the domestic dwelling we don't want that so we've got a split board in this case where a
number of circuits are protected by one RCD so in an event of one of those circuits having an earth
fault only take half the installation would be de-energized and the other half would remain all
so in order to comply to ADS we need hear the appropriate conductors from earthing conductor
protective bonding conductor and the CPC's around the circuit to be in place we need the appropriate
over-current protection device for each circuit so in other words the fuse to be rated correctly
we may offer additional protection for circuits which is very commonplace in domestic dwellings
additional protections offered by an RCD rated at 30 milliamps or below we wouldn't want all
circuits to disconnect at the same time so we either put several RCCB's in or we use RCBO's
and we'll discuss that in a later presentation we know that exposed conductive parts such as
metalclad sockets metallic light fittings and metallic switches need to be connected to the
circuit protective conductor so in the event of have been coming live that they disconnect the
circuit within the maximum times of either point four or five seconds we've also got metallic
water and gas pipe hear which are extraneous conductive parts and again in the event of one
of these becoming alive we need to make sure the circuit disconnects we do not want the
voltage between bonded parts to rise above 50 again we're trying to reduce the risk of three
things being shock fire and explosions we will go on in the classroom to elaborate on all these
points this is a introductional recap video for my learner's with the fact that the IP rating in
the top of any electrical enclosure must be IP4X object exceeding one millimetre cannot
enter in other words dust really primarily and the rest being the side the bottom and the other
side in the front must have an IP rating of at least IP2X in real terms we cannot stick our
index finger into those electrical enclosures we look to have active discrimination which made me
change the selectivity as we move towards the 18th addition between our devices hundred amp incoming
fuse for me here the rule of thumb is that if we move further downstream that we have devices the
ratio of roughly two to one so if we've got a hundred amp fuse here in this installation
the largest fuse in here is 32 amps or 40 amps perhaps circuit breaker fitted another circuit
automatically got a ratio of two to one moving forward that's what we're gonna be looking at
in a set of notes on on fuses as well we look at the discrimination or selectivity between
devices but a good rule of thumb is two to one so as we move through so if you think that a 32
ring final circuit fuse feeds a 13 amps socket the largest fuse inside the plug top is 13 amps
again you've achieved that 2 to 1 or greater than ratio as a rule of thumb between fuses and
the event of plugging something in with a fault you should disconnect the plug top views and not
disconnect the whole circuit by disconnecting the circuit breaker that's it's an earth fault
as a good chance the RCD would have operated in that case so that's a whistle-stop tour of ADS
and we've introduced IP ratings with introduced extraneous conductive parts being non electrical
metal such as the water pipe the gas pipe and the oil pipe we've introduced exposed conductive
parts metallic electrical so motor would be an exposed conductive part the oven would be
an exposed conductive metalclad socket metal metal light fitting would be exposed conductive parts in
this presentation it will link into the classroom work that we do and hope this one's been somehow