- 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 that you've completed the course.
If you're already watching this as part of the CPD package,
we'll crack on.
Now, our next type of protective device
is a little bit different to the ones that have gone before,
because both of those kept circuits safe
by disconnecting them when faults occur.
However, a surge protection device, or SPD,
will quietly and consistently monitor
and keep your installation and connected equipment safe
until it quietly slips away into non-functionality
and requires replacement.
So, what is it, and what does it do?
Well, most electricity distribution systems
around the world use alternating current, or AC,
to transmit electricity from the places that it's generated
and get it to the places that it's needed.
Now, we'd like to think of this AC supplier
as being a beautifully consistent and curvy sine wave,
and for the most part, it is.
However, there are things that can happen
along the supply network and even in properties
that can cause it to become a bit distorted and spiky,
giving us really brief
but potentially damaging spikes in our supply.
These spikes can cause serious damage to our installations,
and especially, the equipment that's connected to them.
And this can get pretty costly.
If you think about how much your TV costs
or other IT equipment you've got plugged in in your home,
one surge event in the supply can completely fry them.
So what causes these costly damaging surges to occur?
Well, there's two sources.
The first is lightning strikes.
Now, you may immediately scoff at this as your house
has never been struck by lightning, and indeed,
it's very unlikely that it ever will be.
This is true.
And to be fair, if your house has the misfortune
to be struck by lightning,
then the devices that we're going to consider
will offer pretty much zero protection to your installation.
The problem for most domestic properties lies
in lightning strikes taking place near to the cables
and equipment spread across the country,
bringing the electricity to your property.
If there's a thunderstorm and lightning strikes the ground
near a supply cable, it can actually generate electricity
into the cable, and this will cause
a potentially damaging spike or surge in the supply
coming into the properties connected
to that incoming supply cable.
The other source of a surge can come
from large electrical loads switching on and off.
So if you are working on a property
near a large manufacturing plant,
it may experience surges caused by the machines
and motors in the building turning on and off.
So that's the problem and what causes it.
How do we counteract this issue?
Well, by the use of a surge protection device, or SPD.
An SPD usually contains either a gas discharge tube
or a metal oxide varistor.
Both of these devices change their resistance
depending on the voltage applied to them.
So when the voltage goes up, the resistance lowers.
So it's a bit like a pressure relief valve on a water pipe.
When the pressure in the system gets too high,
it opens and the water is safely enough to make sure pipes
or more delicate items don't burst under pressure.
An SPD is like a pressure relief valve for electricity.
When the voltage surges or spikes momentarily,
the resistance of the SPD drops momentarily,
which stabilizes the voltage
as current kind of drains away safely.
It's a very clever device that could save
electrical equipment from premature damage.
When the 18th edition of BS 7671 dropped,
surge protection was a bit of a nightmare,
as you had to do some kind of fairly bonkers calculations
to see if it is required or could be emitted.
When the second amendment came out,
it did away with all of that and made the decision
to install surge or not much easier.
Now, regulation 443.4.1,
which covers transient overvoltages
due to the effects of indirect lightning strokes,
states that, "Protection against transient overvoltages
shall be provided where the consequence caused
by the overvoltage could result in, one,
serious injury to, or loss of, human life,
two, failure of a safety service, as defined in Part 2,
three, significant financial or data loss."
So they're all pretty straightforward,
and if you are carrying out installation,
working locations where these could be consequences,
it's unlikely the owners of these properties
would quibble about the cost of an SPD.
But then, the regulation gets a bit weird
for me, personally.
It goes on.
"For all of the cases,
protection against transient overvoltages
shall be provided unless the owner of the installation
declares it is not required due to any loss or damage
being tolerable and they accept the risk of damage
to equipment and any consequential loss."
So for some reason, if you are installing
a consumer unit into a domestic property,
where none of the three indents apply,
it's now down to the installation owner
to decide if they want it or not.
That feels a little bit strange to me.
Surge in a domestic property isn't as serious a threat
as it is in large commercial or industrial installations,
but we don't leave it up to the owner
as to whether they have short circuit protection,
or additional protection in the form of an RCD.
And yet, here, we are putting
this really quite serious decision in their hands.
For me, again, personally,
I wouldn't give them the option.
I'd just install it as standard.
Let me know what your preferred option is
in the comments below if you're able to.
Now, the other thing that you need to watch out for
with SPDs is that they won't trip a circuit
when they've been activated to protect against a surge.
So you'll never have a visible sign that they've done so.
However, over time,
they do kind of wear out internally,
and eventually, they will stop working.
At this point, the SPD will be triggered to show
a different colored panel in this little window here.
So it should, at the very least,
be explained to the homeowner
that they need to check on it periodically
so that it can be replaced with a fresh one.
And it should also form part
of your periodic inspection process
if it's already been installed on the property.
The next video in the series is on AFDDs
and can be found by clicking the link right here,
or by clicking the next button below
if you're taking part in our free CPD package.
Thank you very much for watching.