in this Q and A video we're going to answer the question do i need to bond my incoming water pipe
now this question relates to a video that Gary and Gordon made a while back on a handy
little tool from Knipex called the Bix and it's designed to cut through plastic pipes
now obviously for electricians this is intended to be used for plastic conduit
but it was originally designed for plumbers and as i'm in the middle of refurbishing my kitchen
it made me think of this incoming water pipe here now as you can see the original installer
went to the trouble of connecting bonding conductors to the pipework under the sink here
which is pretty much in line with the practice at the time that the house was built
but is it necessary well in the 18th edition of BS7671 we find regulation 411.3.1.2
under the heading protective exponential bonding we read in each installation main protective
bonding conductors complying with chapter 54 shall connect to the main earthing terminal extraneous
conductive parts including the following one water installation pipes and so on and so forth
however in that edition of the Regs we find this interesting addition metallic pipes entering the
building having an insulating section at their point of entry need not be connected to the
protective equipotential bonding so the simple answer is no this pipe does not require bonding
and when i replace this sink and adjust the pipe work i don't need to connect it back up again
but why not well the answer lies in understanding why we bond let me get out of here and i'll
explain why to understand this we need to go back to the transformer down the road
that feeds my property and what we're about to discuss is applicable to most homes in the UK
at the transformer the star point which is also the neutral connection is connected to earth
via an electrode or rod that's the literal Earth that we walk around on by the way this gives the
transformer a reference for what zero volts is and stops the output voltages going dangerously high
now this earth connection is brought by various means to the property in my case it's via a TN-C-S
supply if it was a TN-S supply then what we're about to discuss in this video is still true
but there is an additional consideration for TN-C-S which we'll discuss in a future
video now inside the house all exposed conductive parts are connected to the main earth terminal so
if a fault occurs inside a load and the metal work becomes live there's a nice low resistance earth
path back that causes a high current to flow and blows the fuse or trips the circuit breaker so far
so good however what if this piece of earth metal equipment is near a piece of metal pipe that
enters the property via the actual Earth now this piece of pipe will have what's referred to as an
earth potential which remember is zero volts just like it was at the transformer
so when this fault occurs a voltage can appear between the earth metal work of the electrical
equipment and the pipe and that can be high enough to give a person touching both at the
moment the fault occurs a severe enough shock to kill how well the answer lies in this very
low resistance path back to the transformer even though it's very low in resistance it
does have a value and if you have a resistance and you pass current through it then there must
be a voltage or potential difference between the two ends in order to push that current along and
because fault current is usually quite high the voltage pushing it along can get quite high too
so between the metal body work of the electrical equipment and the center point of the transformer
there is a voltage and if the center point of the transformer is at Earth potential or zero
volts then this pipe here must be at the same earth potential voltage of zero volts
so whatever potential exists between the earth metal work and the center point of the transformer
must also exist between the earth metal work and this pipe now at this point we could do a ton of
maths to prove this but i don't want to lose you just before the critical point maybe the
team at eFIXX let me do that another time now if we connect a bonding cable from the main earthing
terminal to this pipeline the voltage between the earth metal work and the pipe work will be
reduced as it takes a smaller voltage to push the fault current through the CPC of the circuit
and so the voltage between these two items will be lowered to a safe value because the voltage on
the pipe will actually be brought up to the same value as the main earth terminal so that's one
reason why we bond stuff now for the crucial part if we make this pipe into the property plastic
it no longer has a connection to the literal earth therefore it no longer has an earth potential at
zero volts therefore when the fault occurs there's no voltage difference between the earth metalwork
and the pipe the pipe no longer has a potential of zero it has no potential which can be a little bit
confusing so let's think of it this way the pipe is now the equivalent of the metal frame of a bed
it has no connection to the literal earth it has no earth potential it has no need to be bonded
you wouldn't bond that metal bed frame so why would you bond the pipe now at this point you're
probably thinking but i'd bond it anyway just in case a fault occurred and that pipe work became
live maybe you're thinking what if a cable came to rest on a hot water pipe and the insulation melts
and the pipe work comes into contact with the line conductor we have to ask why would
that happen other Regs would be applied that would keep cables adequately supported and at a
suitable distance from the pipework we can't apply bonding to allow for poor installation methods
elsewhere so there we go one reason for bonding is to reduce the potential difference between the
earth metalwork and electrical installation and any metal work that is connected to the literal
earth that we walk around on if an incoming pipe has that plastic insert or is entirely plastic it
doesn't require bonding but as always we want to hear from you are you convinced that this pipe in
my kitchen doesn't need bonding or if you were in my place would you bond it anyway i must be
honest because of when i did my training it will take every ounce of rational thought i possess to
stop me from reconnecting that clamp to the pipe but whatever the case please leave your thoughts
and questions in the comments section below and as always thank you very much for watching
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