- This video is one of a series that we've made
on the subject of circuit protection
in association with Schneider Electric.
They can be viewed individually,
or you can click the link in the description below
to view them as part of a free online training package
to help you with your CPD,
and receive a certificate
to prove you've completed the course.
If you're already watching this
as part of the CPD package, then we'll crack on.
In this video, we turn our attention
to what is probably the newest device in this series,
at least to viewers in the UK,
the arc fault detection device, or AFDD.
So what is an AFDD and what does it do?
Well, to answer that question,
we need to think about the kind of fault
that it's protecting against.
We've covered most major fault types
when discussing MCBs, RCDs, and SPDs.
However, there's one more fault that can causes problems,
and that's an arc fault.
This type of fault can occur
when a loose connection starts to cause carbonization
of the insulation surrounding the conductor.
If the combination of circumstances is correct,
or incorrect, depending on your point of view
the loose conductor and the carbonized insulation
can lead to electricity jumping the gap
in the loose terminal in the form of an arc.
This arc is another way that an electrical connection
can lead to a fire, causing severe damage.
Because the ARC is not causing
a large amount of current flow for a long time,
and isn't leaking to earth
or causing a surge in the electrical supply,
none of the protective devices
that we've mentioned so far will detect
or disconnect the circuit with the arc fault on it.
So to prevent this type of fault
from becoming a huge problem
and leading to fires breaking out,
we turn to the AFDD.
Now, this technology has been around for some time
in the form of the arc fault circuit interrupter or AFCI.
But in the Second Amendment to the 18th edition of BS 7671,
it finally became a requirement to install them
in certain situations in UK installation work.
So what are they doing to offer protection
against arc faults?
Well, the protective component
in an AFDD is a little different
to previously considered types of protective device.
When an arc fault occurs, it creates an instability
in the current wave form of the circuit,
and turns it from looking all nice and smooth
into a jagged mess,
as the current shoots up and down
to create and maintain the arc.
Now, while this messy waveform may look totally random,
it actually forms a fairly predictable shape
like a signature in the flow of current,
that can be identified by software
as the creation of an arc in a circuit.
And that really is the key to how an AFDD works.
Inside the device there, there is a circuit board
that is loaded with software
that monitors how the shape of the current waveform
is behaving.
Then, when it sees a distorted waveform
that matches the known signature of an arc being formed,
it sends a signal to the mechanical tripping system
inside the device to disconnect the circuit.
Now, if you've been around electrical installation
for some time,
you'll know that some pieces of kit
will generate a tiny spark when operated.
Maybe a light switch feeding an old inductive load
or the brushes on a motor as it spins round.
So will these sparks cause the AFDDs to trip?
Well, no, because in these and other examples,
we're seeing the generation of naturally occurring sparks,
not arcs.
And the monitoring software
inside the AFDD is programmed to recognize this
and not respond incorrectly
by operating when these sparks appear.
So far, so very clever.
But you may be wondering
how many protective devices you'll need
protecting a single circuit.
For instance, an MCB for over current protection,
an RCD for additional protection,
and now in some cases an AFDD for arc fault protection.
Well, the definition of an AFDD helps us
to understand our options here.
In BS 7671, it's described as,
"A device intended to mitigate the effect of arcing faults
by disconnecting the circuit when an arc fault is detected."
So that's stating the obvious that we already know.
But it then goes on to say in the note that,
"Such devices include:
one, a single device having opening means able
to open the protected circuit in specified conditions.
Or two, a single device
with an integrated protective device,
or three, a separate unit assembled on-site
with a declared protective device.
So indent two there,
seems to be hinting at the fact
that you could get a device
offering more than just arc fault protection by itself,
and this is borne out in the rest of the note.
"The integrated protective device two,
or the declared protective device three,
for assembly on-site is either a circuit breaker
in accordance with BS EN 60898-1 98,
or an RCD in accordance with BS EN 61008-1,
BS EN 61009-1, or BS EN 62423."
Now, an RCD that complies
with BS EN 61009-1 is actually an RCO,
and therefore includes over current protection
as well as residual current detection.
So this definition is suggesting
that if you can find a device
that combines all three of these protections
into one product, then it can be used.
And the good news is that they do indeed exist
in various guises.
For example, this one here from Schneider Electric
is a combined MCB, RCD, and AFDD, all in one unit.
So where should we be installing these?
While regulation 421.1.7 states that,
"Arc fault detection devices AFDD conforming to BS EN 62606
shall be provided for single phase AC final circuits
supplying socket outlets with a rated current
not exceeding 32 amps in, higher risk residential buildings,
houses of multiple occupation,
purpose-built student accommodation, and care homes."
So if you are installing circuit protection
to these types of properties,
then you must provide AFDD protection
to any single phase circuits supplying socket outlets up to
and including 32 amps in value.
So because the standard BS 1363 socket outlet
is rated at 13 amps,
then the circuits feeding them must have AFDD protection
in those environments.
So do socket circuits in other environments need AFDDs?
Well the regulation continues,
"For all of the premises, the use of AFDDs
conforming to BS EN 62606 is recommended
for single phase AC final circuits
supplying socket outlets not exceeding 32 amps."
Now that word recommended
isn't like recommending a film to a friend.
According to the guidance
on the language used within BS 7671
found on page 18 of that book,
recommended means that you should do it.
And goes on to state
that the word recommend is an,
"Expression in the content of a document
conveying that amongst several possibilities,
one is recommended as particularly suitable
without mentioning or excluding others."
So you have to do something to mitigate
against the hazard of arc faults,
and the writers of BS 7671 say that this is the best option.
So you're putting yourself in a tricky situation
if you don't use AFDDs on socket circuits.
So there we go,
over the course of this series
we've considered the four main types
of circuit protection found in electrical installations
in the UK,
namely miniature circuit breakers or MCBS,
residual current devices or RCDs,
surge protection devices or SPDs,
and arc fault detection devices or AFDDs.
If you're watching on YouTube,
you're probably wondering
why we've got these double stacked consumer units.
For the answer, watch this video right here.
And if you're watching as part of a free training package,
then to complete this CPD module
and receive your certificate,
please continue on to answer the multiple-choice questions.
All that remains in this video is
to say thank you very much for watching.