How to know if you SPD is working?

How to know if you SPD is working?

Why is a hot site a problem

SPD (surge protection devices) are almost a prerequisite for every electrical and lightning protection system. So, how do you know if your SPD is working? Usually, we’re forced to physically open up live panels to check if the plethora of SPDs is still functioning; very often, this task is made even more complicated on the data side of things, because there is no visual indication at all!

So, knowing electronic equipment is getting ever more critical to our ‘smart’ lives at home and in the workplace, it makes sense to know if your SPD is working.


After this piece, you will learn if you need to test your SPD and why you should or shouldn’t…

Here’s a transcript and audio podcast of the webinar by Sean Passant. You can also visit our academy site where you can view the full webinar on video.

Sean Passant  01:11

Thanks for the introduction. My name is Sean Passant, I’m technical manager of Dean UK. I’ve got quite an extensive history in lightning protection, surge protection, I’ve been involved in industry for about 38 years.

I’m currently the president of Atlas, the UK trade association for lightning protection. And as Ian said, I sit on the GEL61 committee. I’m also a volunteer for IET, and also for CIBSE. And I’m also a visiting lecturer at the CITB National Construction College. So, I get around quite a lot and talking about this subject quite a lot.

How do I know if my SPD is working?

It’s one thing to actually have the SPD in the first place. But we need to know as well, if it’s still working. And we need to know about proving if it’s working or showing it’s working and evidencing that it’s working. And, of course, the best way of doing that?

So a few of the questions we’ll go through today is the basic one.

Do I know if it’s working or not? Should I test my SPD? Is it a good idea and I should I be looking to do on a regular basis? Would a visual inspection, adequate? Is that going to satisfy any kind of regulations that might be there? Could I damage my SPD? Some things don’t always react very well to being tested. So is that something that could happen? And is there ultimately a long term solution? Where are we moving to?

What we what we’re going to be looking at in a few years time when it comes to maintaining our SPD’s or maintaining these protective systems that we have in place.

BS EN 62305

So, a little bit of history on on surge protection in the UK. In August 2006, we adopted a new standard for lightning protection, which was BS EN 62305. And in part three, section 6.2, it became mandatory for you to have type one lightning arrestor SPD’s that’s what they should really be called type one devices on all of your conducts services that came in from lightning protection zone A. So if they appeared in electricians zone A and then entered the building, you have to have a type one device on if you wanted to say that your system was compliant.

Of course 62305 is not a mandatory compliance standard – it’s approved code of practice. But if you want to meet that, you have to have these these type one SPDs in place.

Regulations 443 & 534

Then if we fast forward to January of 2019, the 18th edition wiring regulations comes out. And in there, if you look into regulation, 443 and 534. Type two transient overvoltage SPD’s they become mandatory for a large number of structures, not all structures, but there are four mandatory categories. If your building or project falls into any one of those categories, then you need to have a type one and type two SPD, the origin of your LV distribution system. Even beyond that, you still have to carry out a risk assessment. It’s known as the CRL, the calculated risk level to establish whether you need an SPD or not.


Okay, so generally speaking, it means that across those two different pieces of standards and approvals we’re looking at, over the last 15 years or so, SPD’s have become much, much more common, much more prevalent. Okay, and we’re starting to see them now on almost every project that we look at, really, there’s a surprisingly limited number of buildings now, being built where an SPD won’t be required.

Generally speaking, if you take lightning protection into account that’s going to cover an awful lot of the larger kind of industrial commercial buildings and if you look At what’s in the wiring regulations, then there’s an awful lot of structures that are going to be covered. And generally speaking, is only really domestic housing stock that’s now excluded.

Let’s fine that we all know that we need these. There’s lots of training courses out there available. And of course, people like myself are doing lots of presentations, telling everybody how they need these devices. But there’s still a lot of people within the electrical community, who are a bit kind of in the dark about exactly how to go about dealing with them, after they’ve been installed, what do we have to do. And I think that people are sometimes a little bit uncomfortable with the advice they get.

Should I test my SPD?

There is this general perception that an SPD must be tested, you have to be able to prove it. And it’s something that I certainly hear very, very common. People say to me, “Well, if I can’t test it, I can’t prove it’s working. And then I can’t do my EICR and I can’t sign that off because I don’t know that it’s working and I need to prove that it’s working”. So really want to talk about a little bit about that and establish what it is that you really need to do. And the requirements that are there to be able to say that everything’s okay.

The first thing you should do really is have a look at an SPD. And see what information is on that so that we can then establish what we might want to do.

Here we have a combined type one, type two and type three SPD, it’s a three phase or neutral device. And this particular device is suitable for a TT earthing system. So that’s the kind of device that we’ve got. And we’ve got quite a lot of information here on the SPD. And that required information will change slightly from manufacturer to manufacturer. But generally speaking, because of the standards, governing SPD’s, a lot of it is fairly common. So although this is a Dehn device, we’re going to look broadly going to be the same for any other manufacturer.

Incoming Terminals

So we’ve got our incoming terminals, L1, L2, L3 and neutral, those are the terminals there. You’ll notice that the writing is both ways round. So you can have the device installed wither way. SPD’s have no spatial awareness, so you don’t know if they’re upside down. And it’s only really us as human beings that determine whether something is upside down or not. So it could be installed either way around and therefore different incoming terminals.

Vital Technical Data

Then we’ve got an awful lot of technical data. That’s going to be specific to the device. So we have a part description on there. We have a part number on there, those are unique to the manufacturer. But then we go into a whole series of pieces of information that’s gonna be really important for you to look at, and check and make sure that it’s appropriate for the system you’ve got.

We’ve got Un, that is the nominal voltage for the SPD. In this case, 230 volt 50 hertz, you then have Uc that’s the maximum continuous operating voltage, in this case, 255 volts. We’ve got by Imp, that is the impulse current. And it’s very specific to the type one characteristic of this device. So, it is specific to its ability to deal with lightning energy, and in this case is 25k per phase.

And because there are three phase and neutral as 100k. Then we’ve got ‘In’  and that is the normal impulse current. Again, that’s very specific to the type two characteristic. And here again, 25k per phase, 100k overall, because we’ve got three phases and neutral. Then we’ve got OUC, which is the open circuit voltage. And again, that’s very specific, it’s specific to the type three characteristic of the device. And in this case, it’s been tested at six kV.

Voltage Protection Level

Then finally, we have ‘Up’ which is the voltage protection level. Now voltage protection level can be read and understood if you prefer. It’s easier to understand as the trigger point, the point it will start to do some work when the SPD has got to start having an effect. So here we have equal to or less than 1.5 kV. So what you can broadly say is that any kind of overvoltage event up to 1499 volts is not going to have any reaction from the SPD. The SPD is not going to do anything. It is going to start working once we get up to that 1.5 kV range.

That is broadly speaking because within the wiring regulations for 44.3 there is a requirement for a built in withstand for equipment, and the very lowest category of that the most sensitive equipment has to be able to cope with 1.5 kV anyway. So, your SPD is there to start protecting at that level that’s fairly normal.

Status Indication Window

We then have this status indication window, we’ll come back to that in a minute. But as you can see, it’s nice and clear at the moment is green. And that’s obviously telling us that devices is operating.

Earth & PE Terminals

Now we’ve got our Earth PE terminals, and you can see there are two of them. In this case they’re common inside one marked with the earth symbol one mark is PE and finally we’ve got our volt three contacts here. They are to be attached to some kind of form of remote monitoring. So again, a form of indication knowledge about your SPD and what’s going on with your SPD without having to Test.

They can be connected to a building management system that could be connected to a lamp or a buzzer. So, if this SPD was tucked away in the depths of a big form four main incoming panel, and you couldn’t easily see it and couldn’t easily see that visual indication window, you could use those remote contacts to go to a lamp or a buzzer. If anybody who happens to be passing by and saw that, they’d be able to know that there’s something wrong with the SPD and the device is not working.

You’ve got two things here already the status indication window and the volt, three contacts, they’re going to tell you about your SPD without necessarily having to resort to getting out our tests.

Broadly speaking, SPD’s, have to have some kind of indication on them. Again, that’s part of the testing and development standard recipe days, that’s BS EN 61643 here in the UK. And broadly speaking, they fall into two categories. It’s either an LED, which is going to operate from a battery or a power source of some sort. Or more often than not, they’re going to be some kind of flag system that’s certainly what we have here. This will be the same for a number of manufacturers will have this type of system.

Thermodynamic Control

Now, it’s very, kind of given the flashy title, the very grand name of thermodynamic control. In actual fact is very simply a piece of soft solder. When the SPD does work, it will get warm. When it does a lot of work to the point where it may fail, the soft solder will melt. And you will see that there’s a spring action that we show here. The green flag will spring out of the way and it will leave a red flag behind and if any one of those indications on this SPD, you’ve got one per phase. If any one of them was to go red, you would know there was a problem with your SPD.

The other thing to bear in mind as well, of course, is that type ones and type two SPD’s are installed in parallel. Because they’re in parallel, they’re unusually there’s no load going through them. When the thermodynamic control kicks in, is going to stop the SPD working and it’s going to put it in a really safe open circuit condition whilst installed in parallel, so it’s not really going to be a problem for us. It’s going to tell us that it is not working because it’s going to turn red. Broadly speaking, it could be like that for a while until somebody notices it and it’s not going to cause any problems.


It’s also worth noting as well, what your SPD is rated to all SPD’s have a built in withstand capability. Okay, so it doesn’t actually mean there’s a fuse in it. But there is a withstand capability built into SPD in case the one you’re looking at on the screen. So 125 amps, and they vary some 167, 250 and lots of others. If your rating of your SPD is equal to or less than your supply current, then you don’t need any overcurrent devices. You don’t need any OCPDs, so, no MCB, no fuse. None of those things are required and the SPD is going to be safe dealing with that amount of energy.

What the status indication window gives you is a basic ability to understand and know that the SPD is functioning within its basic parameters. So that is basically proving to us that normal voltage is okay. Otherwise it will turn red is basically proving to us that the nominal discharge current ‘In’ is okay. Otherwise it would turn red. And it would also be telling us that that voltage protection that will be ‘Up’ or the trigger value is okay. And that’s trigger circuit is operational. All of those things are really being proven by the fact that it’s remaining red, because if any of them failed. It would be enough to trigger the thermodynamic control and to change it to red status. And you would know then that there was something wrong.

Do we really need to be doing testing?

So if we’ve got all that information, we haven’t had to get our test meter out, then we have to start asking the question is, do we really need to be doing the testing?

Because SPD is becoming much more common. You can understand Of course, that the manufacturers of multifunction test devices want to give some kind of offer to that. They think that there is a need to test these. So there’s an awful lot of the moment of new devices coming onto the marketplace and a lot of manufacturers saying that their new device has the ability to test an SPD.

Nominal & Maximum Voltages

But you have to have a really good look at that and question them a little bit more. Because all they’re really doing his industry circuit and checking the nominal voltage. If you use most of these meters and put them onto your SPD. What it’s going to tell you is you’re going to see that nominal voltage trigger coming up so you will or that maximum continuous operating voltage is what’s going to come up that’s what you’re going to kind of see you’re not going to say anything else is not really going to be telling you much more.

What it absolutely doesn’t do the modern day multimeter. It doesn’t test the true dynamic function of the SPD is not a thing. Depending on what type of SPD you’ve got either the spark gap, the gas discharge tube, or the metal oxide varistor is not testing that is not testing and proving that dynamic function and then it does a lot of things. So it’s not a bespoke tool, okay. It’s not a dedicated tool for the job. Really, they are aimed at domestic electricians and house bashers. And that is largely because domestic electricians feel that they need to test things. They believe they need to be able to test something to prove it.

I think what we’ve shown already is there’s lots of information and things you can do where you don’t need to. And it’s also worth bearing in mind, of course, it’s not possible to test a type one device. You can’t actually test and prove a type one device. And I’ll give you an example, why.

Lightning impulse generating equipment

This is the lightning impulse generating equipment, let’s get our lab in Bavaria. Okay, now lab overall is about 1000 metre square, this is the 10 350. That’s the wave shape we use for testing type devices. This is the lightning impulse generator that creates that 10 350 for us. As you can see, there, we’ve got a double crowbar system with lots of lots of capacitor banks in there. Okay, it’s quite big, it needs a lot of energy. And it’s simply not possible to fit that in the back of electricians van.

So the only way to test a type one device really is to make a trigger. So it’s to expose it to that high level of 10 to 15 lightning energy. And what we’re seeing here is that’s just not possible you couldn’t carry that around with you.

Bespoke test devices

It’s not to say it’s actually impossible to test an SPD, it’s not. But usually, there’s only going to be the type twos and type threes. And you should really be using a bespoke test device.

Here we have an example of one of those. This device only test SPD’s, and it is specifically for testing that dynamic function is going to test improve the the discrete component within the SPD that offers you that protection is actually doing its job.

Additional Adapters

As we say, for type two and type three, you can get additional adapters for these devices for your data. So if you want to test the data SPD, that’s fine, but you should also be aware that for the most part, these days, a lot of data SPD’s frequently have some kind of self-testing function, or they have some kind of warning built in and are able to tell you that they failed.

Now, some of those are very, very simplistic, they will quite simply interrupt your supply. So they will, they will basically stop you from receiving that data. That is the way they are telling you there’s something wrong. Some of them are a bit more advanced than that. They have other means in terms of having LEDs to warn you remotely, they can also have RFID. There’s a number of other ways that these these SPD’s can communicate with you. And the reason for data SPD is having that is by the very nature, they are controlling communication. So it makes it easier for them to communicate with you rather than it is with the LV devices which are not typically communicating.

BS EN 61643

Is there actually a requirement to test and should you be doing it? Well, SPDs these are tested and developed in the first instance to the international standard is IEC 61643. And we have a UK specific version of BS EN 61643. And that is for the development of low voltage surge protection equipment.

Type 1

For you to be able to say that your type one device works that meets that standard, it has to be tested to 20 exposures of 10 350 microsecond lightning energy. We show an example of that, and the red on the graph at the bottom there, so it’s 20 exposures.

Type 2

A type two device, same thing. Again, it’s 20 exposures, but this time it’s to the 820 microsecond wave shape. We show an example of that in green on the graph at the bottom.

Combined devices

So a phrase that we hear quite a lot in search protection is people saying that they are voltage fuses, and quite a common phrase that we hear from people in North America is one and done. And there’s this kind of mistaken idea that as soon as SPD sees some of that voltage that is going to deal with it, but then it’s also going to fail. SB is actually not voltage fuses. They’re not designed to fail, they’re designed to give you a lifetime of use. And as you can see, the testing standard alone requires that device to be able to deal with at least 20 exposures to the wave shape that is supposed to be protecting.

If you’ve got a combined device like a combined type one or type two, which is quite frequently quite common these days, it has to be tested to both of those protocols. So the device in testing is effectively exposed to 40 different events 20 of the lightning way shape and 20 out the transient wave shape. So really is quite a lot of exposure. The devices are not designed to fail they will really give you a long, long, long lifespan.

So when I first came in to the lightning protection industry in the working at height industry, you won’t be surprised in a presentation about surge protection to suddenly see a harness and lanyard there.

Testing Safety

When I first came into the industry, in the 80s testing safety harnesses was big business and companies would send their harnesses away to be tested. And I think was because they didn’t understand. In fact, I know they didn’t understand what was actually happening to that harness. So the harnesses were sent away and it was a 15 kilonewton tensile load was applied upwards at a 10 kilonewton tensile load was applied downwards. And the same is true of the land yard as well. So the harness and the landing are being stressed and weakened by that testing process.

So if you’ve had a harness for a year, and you’ve never ever had an incident. Then it’s almost apart from maybe being a little bit grubby is probably in the same conditions when you get out of the bag. If you then send it away to be tested, it’s then being put on the load, it’s been stressed, it’s been weakened, and when you get it back, it’s no longer as good as the hardest you first bought.

When people realised this, broadly speaking, most people stopped testing harnesses. They simply introduce the regime where they would buy harnesses more frequently, visually inspect them record their use, but ultimately, they would not be testing them because they put it on the load. And I think that’s what most people do these days. And as a result, of course, the cost of harnesses has come down. So because more people are buying more harnesses.

That analogy really is to explain the situation with SPD because it’s broadly speaking the same for type two and type three SPD.

Life span

So if you think about that 20 events criteria, you can consider that the device has a kind of anticipated lifespan of being able to quench 20 transient events. Quenching is the term we use in SPD’s, in terms of dealing with it, spotting it, triggering and sending it safely down to earth.

Flash density levels

If you look at the typical flash density levels in the UK, and the size of the structure in the UK, were to carry out broadly speaking a very generic risk assessment. A like commercial structure might expect to see a transient event in the UK, once every three years some much more frequently, some maybe slightly less frequency, but I’m trying to be quite general here in my description.

Physical testing regime

So generally speaking, once every three years would not be particularly surprising. If you introduce a physical testing regime, where you’re going to actually use a test metre and put a test the dynamic function of that SPD, you’re stressing the SPD’s components. So you could be shortening the lifespan of device from 50 to 60 years, to less than 15 years. Because if it sees an event every three years, and you’re testing it every year, in the course of 15 years, you could get dangerously close to that 20 events that the standard says it has to be able to deal with so you could actually be reducing the life of your SPD.

Now you’d imagine that you’ve got a particularly overanxious overzealous young apprentice, and he’s been asked to do some testing by his boss, and he wants to show to his boss that he’s very competent, and he knows what he’s doing. And he’s got everything right and everything correct. And so instead of just taking the test result, once he takes it again, and then probably a third time, and then maybe a fourth time just to check. Every single time he pushes the button, he stressed in the SPD, and in theory could potentially be reducing the life of that SPD. So don’t really want to be doing that. That’s not really the idea.

Visual inspection

There’s absolutely nothing, either in 62305, or in 7671, the wiring regulations. There’s nothing to tell us that we should do. I’m very lucky that I’ve got a colleague that sits on the wiring regs, he tells me that absolutely no plans to introduce that either. At this moment in time, the advice is a visual inspection every 12 months, or immediately after a suspected event is perfectly adequate.

So a visual inspection of that status indication window. Check the cables to make sure that they look okay, check the if you’ve got volt-free contacts, check to make sure there’s an installed, check the earth is still installed. Just check to make sure there’s nothing looking like charring or damage or cracks or anything like that. That’s all you need. Do that every 12 months, and that’s going to be absolutely fine. And you’re not going to be giving yourself any issues and you are going to be proving that your SPD is still installed and still work.

Is there a long term solution?

Well, in a word, yes. Yes, there is a long term solution. And I would say this is true of all SPD manufacturers, okay. SPD’s are getting smarter, they have to everything in our life is getting smarter. We live in a world now where our fridge can be connected to the Internet and it will tell us if we take milk out and don’t put it back in that we need to buy more milk. Okay, so SPD’s have got to follow we need to be making them smarter. Okay, so all manufacturers are working hard to develop more intelligent, more capable solutions. And one of the main things that customers want and we recognise as manufacturers is the ability for the SPD to give you more data. Tell you more things about itself and about your system.

As an example here we have some data SPD’s. Typically speaking in the first instance when data SPD’s came out their way of telling you that there was something wrong with them was that you would lose supply, you would lose service, okay, they would interrupt the signal and you would then think okay, I’m not getting the signal anymore. You would go and have a look and you would see because of the visual indicator on the SPD, that there was something wrong, then we moved to using RFID. And quite a lot of data SPD’s have RFID. They are broadly speaking, able to be addressed. Then constantly every few seconds checking to make sure that they’re okay.

The problem with RFID is sometimes there’s potential for it to cause issues with other signals around and also is quite old technology, it’s quite hard to programme RFID on an SPD in itself, particular data speed is quite small. So it can be a little bit tricky. And broadly speaking, they don’t often measure and monitor a lot of SPD’s at a time, frequently, you may only be able to monitor 10 or 12, SPD’s at ago.

What’s the solution?

What we have here is a newer solution. Here we have the yellow SPD’s in the middle, and the grey, the side is the monitoring. We have a light source on one side, and a passive reflection tube on the other. And this is basically passing a beam of light through and back through and back and through and back, and so forth. And as it goes through each time, it is checking a different component. If any of the components fail, that a flag will drop down, it will cut that light beam. And it will then send you the information to let you know that the light is no longer getting through and there is a problem of your SPD. And when you come along and have a look, you’ll see again on the front rows SPD’s.

They’ve all got visual indication, and you will see which one of those has failed. Then you will then be able to take that out and swap it and you’ll then be able to go back to having full service.

So this is a much better way of monitoring. And in this scenario, because it’s light, it’s not going to interfere with anything else. And you can do up to 50 SPD’s at a time with one unit. Okay, so pretty straightforward, pretty good and a lot of data SPD’s are moving this way. And this is a system that a lot of manufacturers are adopting.

What about LV power?

LV power is a little bit different. You do have to be a bit more careful and you probably will need a more dedicated solution. Here we have an example where you can see the grade device in the in the artist’s impression attached to a red SPD next to it. This is a means of recording all of the data that’s going on in your system. And it can also monitor your SPD and tell you what’s going on in your SPD. The day record device is in effect, a permanently installed power quality monitoring device.

You can see here, it’s got some Rogowski coils, which are able to carry out some monitoring. There are some probes, temperature probes, things like that is monitoring those kind of things. And you can see that it’s also connected again via a cable back to our system and it’s giving us more and more information. And it’s deliberately intended to be paired with an SPD. So it’s telling you what’s going on with that SPD as well as everything else.

Permanently installed Power Quality Monitoring

So it’s checking all the things you’d expect from power quality monitoring, so amplitude, flicker, harmonics, dips, frequency, etc. It’s going to tell you about your voltage, current, your power and your energy. So it’s telling you what your system is doing. If you’re being efficient if you’re not being efficient, etc. You can monitor mains current over voltage and temperature. Which again is going to help us to eliminate arc fault issues because we know that some of those rises and peaks and spikes in temperature can ultimately lead to an arc fault.

Most important things instead of SPD’s is that is monitoring the impulse current for both transient and lightning events. Okay, so that’s your 820. If you’re type two, and your 10 350, that’s your type one. And it’s going to measure the duration, the rise time, the total charge and the frequency and event this is a device it’s going to tell you just how often your SPD works. It’s effectively proving that your SPD is working and operational, but it’s also showing you how often it’s triggered and what type of event has taken place. And it will give you all of that information uploaded every 10 seconds out to you can download it to your mobile device.

So you can be have one of your shift engineers sitting in the cafeteria, having a cup of coffee. He will be a text message sent to him from the cloud basically telling him you need to go and have a look at the SPD. There’s something wrong with it. All of it is downloaded as well as full colour charts so you can have a look and and see exactly and analyse that data and see what’s going.


So any questions whatsoever on what we’ve seen so far, in terms of visual inspection of SPD’s testing of SPD’s. How do we prove that SPD’s work and in terms of the future, that big data picture in terms of collecting and harnessing data so that we can use it and we can then improve what we do and we can know more about your LV distribution system effectively through our SPD.

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