Should you test an SPD?

With the increase in the application of surge protection devices to our electrical installations, we have seen an increase in testers being marketed as able to test an SPD.

This raises the question: Should we test SPDs?

The simple answer is no. Any test on an SPD will involve passing voltage though the device to ensure activation, this passing of the voltage will degrade the components within the SPD and therefore shorten the lifespan of the device. The SPD does not know the difference between voltage for test purposes and a surge which it is designed to remove from circuits.

SPDs have certificates of conformity to demonstrate that they are built to the relevant part of the BS EN 61643 series for that type of device. If the SPD is unable to provide protection, weather this is due to a fault within the device itself or that the device has come to the end of its life span, the indication on the device will show the failure.

Realistically, any simple tester that can apply voltage will demonstrate that the SPD will activate when required, just because you can do something, does not necessarily mean that you should.

If you require any assistance on surge protection, please feel free to contact me.

Kirsty Johnson MIET

Site Survey’s for Surge Protection

As a company we have always offered site surveys for complex electrical installations, but during the pandemic, when we couldn’t travel, we also found that we can offer an excellent service remotely, which helps us get to site faster. There as some situations, where an in-person site visit is still recommended, but for the majority of sites, a remote site visit is preferable.

  1. What type of situation would you recommend a company requests a site visit?


We can specify the surge protection required for the majority of sites with a simple phone call to our office, but sometimes site visits are recommended for complex electrical installations, usually where there will be multiple incomers, external lightning protection systems and installations where surge protection is being installed due to large amounts of previous damage.


  1. Where would you suggest using an on-site visit, rather than a remote assessment?


In person on-site visits would be recommended for very complex electrical installations, installations where internet connectivity may be an issue and also installations where data protection and safe guarding mean that video calling is prohibited.


  1. How does a site visit generally work?


Before arranging the appointment, whether in person or online, we will usually have an in-depth conversation with the electrician in charge, many sites we can specify without the need to actually come to site, so this is where we will usually establish the need for the site visit. Once the need has been established, we will work with the electrician to work out which method of survey will be the most beneficial.


Once on site, either in person or remotely, we will usually start the survey at the main incomer (or each main incomer individually, if it is a very large site) and assess the needs, while having discussions with the electrician regarding installation and location of devices. We will then proceed to look at sub distribution boards and finally specific equipment which may require individual protection. At this point we will have a discussion with the electrician to assess whether there are any additional things to consider for the installation, such as PV systems and EV chargers.


At the end of the visit, we will go away and produce a report with our findings and recommendations according to the latest regulations, which will be sent to the electrician as soon as possible.



  1. What tends to be the most common misunderstandings around the requirements of surge protection that you generally come across?


One of the most common misunderstandings is that surge protection can be installed at the main incomer to protect the entire installation, surge protection needs to be considered for the main incomer and then every distribution board over 10 meters from the incomer, to provide protection for the installation. If there is an external lightning protection system installed, this is even more important. This will mean that every cable that enters or leaves the installation requires a type 1 SPD installed to meet the requirements outlines in BS EN 62305.


  1. Are you finding there are common themes with the types of recommendations you are making (more surge protection required, for example)


I am finding that more thought is now being given to the protection of specific equipment pieces, such as fire alarms and data racks within installations. This is usually the sensitive equipment that is vital to the installation, in terms of safety and reliability.



  1. Give us an example of a recent/interesting visit you’ve made and how that went for all parties


My only in person site survey in recent times, was an extremely complex site, with multiple incomers, back up generators and external lightning protection systems.

The client had got in contact with us due to issues with an BMS panel that had been upgraded, due to the majority of the electrical services being underground, a remote session was not possible.

On visiting the site, it was quickly established that there were multiple external lightning protection systems, without adequate surge protection installed, but this was not what was causing the issues with the BMS systems.

On further discussions with the site engineers, I was told about the generator testing that happens regularly. It was my opinion that this was what was causing the damage to the BMS controls. It was discovered that the BMS systems had recently been upgraded, there were historically no issues with the old panels, but the generator testing did align with the damage that was seen on the newer panels.

As the newer controls were more sensitive, the same overvoltage was now causing damage. A plan for the rollout of site wide surge protection was then put in to place to help overcome any future issues with upgrading technology.

If you have any further questions, or would like to discuss a potential site visit, please do not hesitate to get in touch.

Kirsty Johnson MIET

01484 851 747

Surge Protection – FAQ’s

Since the release of the 18th edition there has been an increase in the use of surge protection devices, this is only growing with the additional requirements in amendment 2. As always, with a new subject matter, there is a few frequently asked questions that hopefully I have covered below:

Question Answer

Will an SPD need replacing after every surge?


No, an SPD is deigned to take multiple surges and internally reset after each over voltage. An SPD will only need changing at the end of its life (the warranty is manufacturer dependent) and this will be shown in the status indication on the front of the unit.
When do I need to use a type 1? With the increase in availability of consumer units with the SPD already installed, it is becoming more of a consideration as to if this is the correct device. A type 1 will be needed in a domestic installation, if the property is supplied via an overhead cable. Outside of domestic installations, a type 1 device will also be required if the structure has an external lightning protection system.
Why do some manufacturers need an MCB before the SPD? According to BS7671, all SPDs shall be protected from overcurrent, this can be done with an MCB or an internal fuse. As a company we specify the use of MCBs with all of our devices. The MCB will provide a back up in case of a failure within the SPD, while also protecting the cable and giving a point of isolation for the SPD.
How do I measure the cable lengths to ensure I meet the BS7671 requirements? If the SPD is installed within the consumer unit, cable lengths will automatically be suitable. When installing outside of a consumer unit, you must ensure that all cables combined are less than 1M in length. Length A will be from where you take your live supply to the MCB (this is 0 if the MCB is on the busbar), Length B is from the MCB to the SPD and Length C is from the SPD to the closest earth point (not the MET). For a more detailed explanation of this, please look at our installation guide available on our website.
Will an SPD installed in the consumer unit protect the whole domestic property? An SPD in the consumer unit will massively reduce the risk of any internal damage within the electrical installation from overvoltage coming from the mains supply. Obviously, there are other routes of entry in to the electrical system, via aerials, telephone lines or any external cables, but there is no requirement in BS7671 to protect these routes.
Do I need to install type 3 devices in a domestic installation? There is no requirement to use type 3 devices. The type 2 on the consumer unit provides an enhanced level of voltage protection for the installation. Type 3 devices would only be used in specific specialist circumstances.


I hope that has answered some of your questions, if you have any questions I haven’t covered, or would like any specific help with an project or installation, please feel free to contact me directly at and for more information, please visit our website:

Electric Vehicles and Surge Protection

By their very nature, EV chargers are both sensitive (limited impulse withstand capacity) and exposed to overvoltage. In fact, quite a few EV charger manufacturers will specify that an SPD should be installable or mention surge protection in the warranty details.

So where is the risk of damage?

EV chargers are installed outside; therefore, they are liable to experience the effects of nearby lightning strikes. There is an increased risk of the charger being damaged from the effects of lightning, if the installation has an external lighting protection system, or if the EV unit is supplied directly from the main incomer of a building fed by an overhead supply.

Damage could also come from the installation, in the form of switching overvoltages. Overvoltages could also come from the supply network, or be created by equipment within the electrical installation. This form of repetitive overvoltage could damage the sensitive components used in EV chargers.

Also, EV chargers can cause issues with the electrical installation. We have to consider that any cable that enters an installation can bring with it the risk of overvoltage, as mentioned previously, the effects of nearby lightning strikes, are a risk to the electrical installation, along with the EV charger unit. Inverter technology can produce overvoltages, which can potentially cause damage to sensitive equipment inside the installation.

So, our risks are:

  • Damage to the EV charger
  • Damage to the car
  • Damage to the electrical installation

Using section 443 in BS 7671:2018 amendment 2 we can consider the requirements of SPD’s. Just as a reminder, 443.4 states that:

Protection against overvoltages shall be provided where the consequences caused by over voltage could:

  1. result in serious injury to, or loss of, human life
  2. result in damage to a safety service (deleted by corrigendum May 2023)
  • result in significant financial or data loss

For all other cases an SPD shall be installed, unless the owner accepts the risk of damage.

The obvious starting place would be to consider the result in significant financial loss. EV technology is expensive to install, not just from a charger perspective but also for the car itself. We also have to consider the implications involved, if a charger was damaged and the user could not charge their vehicle.

There is also the risk to life implication that must be considered if loss of neutral technology is used. These devices are designed for use in installations where there is a PME earthing arrangement. When the PEN conductor is broken, the neutral voltage can rise with respect to true earth and the normal protective earth forms the return path for any current that could flow. This could cause a car plugged in to charge to become live, if contact was then made with the car there is a danger of electric shock. Most EV charger units now rely on this technology to disconnect the supply to the charger in the event of a fault.  If this technology is damaged however, such as by the effects of lightning or some other form of overvoltage, this disconnection will not happen. Meaning that in the event of a fault, an electric shock could occur.

If the installation has an external lightning protection system, we also have to consider the requirements in BS EN 62305. Any cable that crosses the lightning protection zone 0 to zone 1, requires a type 1 SPD to be installed, to protect the installation. If, therefore, you are installing an EV charger (or bank of EV chargers) on an installation with an external lightning protection system, the DB supplying the external circuit will require a type 1 SPD to protect the installation, and another type 1 device in the feeder pillar supplying the chargers to protect the chargers from lightning effects on the external cable.

With all EV installations, I would recommend an SPD, this is to protect the car charger, itself, along with the installation.

I hope this article has provided some guidance on the requirements from BS 7671:2018 amendment 2, if you have any further questions, or would like to participate in any of our free CPD sessions, please do not hesitate to get in touch.

Kirsty Johnson MIET

01484 851 747

SPD Training Academy

I am proud to announce that the team at Surge Protection Devices Ltd are launching an SPD Training Academy.

What is the SPD Training Academy?

The SPD Training Academy is a new addition to our website offering. We aim to provide attendees with up to date information regarding surge protection through our range of webinar sessions.

All of our webinars are completely free and we are CPD certified, so every attendee will receive a CPD certificate. All webinars are given by Kirsty Johnson, our technical sales director. Kirsty sits on the JPEL panel to assist with the wiring regulations, so is well placed to give training on Surge Protection to the latest regulations.








What topics are covered in the webinars?

SPD Ltd currently has the following courses available for immediate sign up:

Basics and the 18th Edition: This session is aimed at electrical contractors who may have limited or no experience with surge protection to give a basic understanding of what surge protection is and why we use it, through to how it works and where it needs to be installed. We will then cover the 18th edition guidance to finish off the session.

Apprentice: Introduction to SPD’s: This session is an apprentice only session where we will cover the fundamentals of surge protection to prepare apprentices to do the full basics and the 18th edition webinar (above).

Focus Training: Surge Protection Devices: These sessions are bespoke sessions for Focus Training learners, please contact your lecturer for further information.





Lightning and Surge protection in Commercial and Industrial installations…

Lightning and Surge protection in commercial and industrial installations









Following on from my previous post on 21st November about Lightning protection in domestic installations we move on today to discuss lightning and surge protection in commercial and industrial installations.

BS7671 states that Surge Protection Devices (SPD’s) must be installed where the consequence of an over-voltage could result in an interruption of commercial and industrial activity, which in most commercial / industrial installations will be the majority of distribution boards.

When considering which device to install, we need to look at where on the electrical supply you are working. If you are working on a main incoming panel, you will need to assess whether the building needs a combined lightning and surge device (Type 1+2+3) to protect against direct lightning strikes. As discussed in the previous article, only buildings which are either fed by an overhead power line or have an external Lightning Protection System (LPS) will need a Type 1+2+3 device, otherwise a Type 2 device is sufficient. If you are working on a sub distribution board that doesn’t feed any external circuits, the device you will need is a Type 2, which will protect against any transient over-voltages.

If you were looking at protecting a whole commercial or industrial installation, rather than just the board you are working on, firstly a device will need to be installed on the main incomer, then any sub distribution boards more than 10 meters away will need their own protection. Unfortunately, surge protection has a limited range of protection, which is limited after a 10 meter radius, and as surges are most often caused inside the electrical installation rather than transmitted from the main incomer, it is important to ensure that the devices are installed as close to the equipment you wish to protect as possible.

If you want to discuss this any further please call our specialist surge team on 01484 851 747.

The Importance of CPD Post-Pandemic

The industry view of Continuing Professional Development (CPD) has really shifted during the pandemic. Electricians having more free time on their hands, turned to upskilling themselves, but I think this has really highlighted how little training and further learning was being undertaken by the industry pre-COVID. Competence scheme providers have long been advocates of CPD, along with industry groups, such as the E5 group regularly encouraging contractors to ‘level up’ by increasing their knowledge.

As a manufacturer in quite a specialised area, I have always seen CPD as an extremely important area of the industry. With new technology emerging so fast, electricians run the risk of being left behind if regular CPD is not completed.

Working for a company that specialises in surge protection, my career has always has always centred around training and CPD. Before the 18th edition, surge devices were not widely used within most sectors of the industry, so my job entailed lots of educational talks, seminars, CPD events, appearing on industry podcasts and writing magazine articles. In fact, pre pandemic, I was driving up to 1000 miles a week covering the UK and Ireland covering these events! So, in March of last year, when I was grounded, like most people, for the first few days I didn’t know what to do with myself. After discussions with colleagues and friends, I realised that I could carry on delivering quality training on a virtual basis and that led to launching the SPD Training Academy.

I was absolutely overwhelmed with the response and one live session a week quickly became a daily event! I have now trained thousands of electricians, specifiers, electrical consultants, lecturers and apprentices throughout every level of the electrical industry, all for free, without leaving the office. I have had some lovely feedback and my sessions have been met with such gratitude, that I think it has really highlighted to me the lack of free, understandable, CPD being offered throughout the industry.

The pandemic and the following lockdowns gave people more time. It’s crazy now to think of all of the important training and CPD on vital issues, that was missed pre-COVID due to the pressures of working as an electrician within the electrical industry. CPD gets put on the back burner, especially for small contracting companies and sole traders, who have to lose income to complete valuable training. I have seen so many people on social media who have made massive accomplishments in learning and training during lockdown, that during a normal period, would have been impossible.

The availability and suitability of free CPD opportunities is something that as an industry we need to address moving forwards. From my point of view, I feel that manufacturers have an obligation to offer CPD opportunities to anybody that wants to learn. There has been a massive increase in the CPD offered during the pandemic, and I do not want to see this decrease as we move closer to a normal life.

At SPD LTD, I wanted to ensure that people could still take part in training with me, even if they are back at work. So, alongside my live sessions, I have taken the step of breaking down my training webinars in to 10–15 minute modules, which can be watched on demand. This means that contractors will have the option of partaking in a live session with me where that can ask real time questions, or if the times and dates don’t suit, they can log in and do the training session in their own time then contact me directly with any questions.

I would like to see more manufacturers offering CPD as a way to help the industry, rather than a sales exercise. I have given training to contractors and consultants that have openly told me they don’t use my company’s products. What is important to me, is that the education is there to ensure that the correct devices are selected and installed, that people understand the wiring regulations regarding surge devices and understand why they are being installed, not what brand of SPD is being used.

As much as we are all looking forward to being back to normal, I hope that as an industry going forward, we won’t forget the value of CPD and its importance to ensure that we, as an industry, stay relevant and up to date.

Lightning Protection in Domestic installations…

Lightning Protection in Domestic installations…

Following on from my post last week about surge protection in domestic installations today I want to talk to you about lightning protection in domestic installations.

Lightning Protection only needs to be installed on a domestic installation when the property is directly fed by over head power lines, or has an external lightning protection system (LPS) on the property.

Having an external LPS on a domestic property is rare, because the LPS system is designed to protect the physical building in a lightning storm. Most domestic properties are deemed not at risk from direct lightning strikes. The LPS is usually cross-bonded to the main incoming panel, so generally when an LPS is struck by lightning, 50% of the energy goes to earth through the earth rods, then 50% of the energy comes into the building via the cross-bond. Please see the photo below.








This is the same principle with overhead power lines, except as the L&N supply come directly in to your incomer, if the overhead line is stuck by lightning the whole lightning impulse is then transferred through to the domestic electrical system.

This is why you need to install a combined lightning and surge device (Type 1+2+3) on the main panel where the LPS system is cross-bonded to, or where overhead power lines are connected to the internal electrical system.

If there are any consumer units more than 10-15 metres away from the main incoming panel then a surge device (Type 2) will need to be installed. This surge device will be taking care of all the surges generated internally to the property.

Please note that a combined lightning and surge device (Type 1+2+3) will not only protect against direct lightning strikes but also internally generated surges too.

If you have any more questions please get in touch with our specialist surge team on 01484 851 747.

Why do we need to fit domestic surge arresters?

Surge protection has made it’s way into the Wiring Regulations over the past few years, which has left everybody questioning the need for surge protection devices, and quite rightly so.


Surges are temporary rises in over-voltage and can also be referred to as spikes. These spikes are happening all the time within a domestic environment, e.g. when lights are turned on, a washing machine / tumble dryer starts up and especially when the power goes off and comes back on again. Now, these short spikes in the voltage will run around the electrical system and degrade the components inside domestic appliances. This basically means that appliances are only lasting a fraction of their lifespan due to seeing surges.


We are not really experiencing any more surges than we did 30-40 years ago, the problem we are having in this day and age is our technology. TV’s in the 70’s / 80’s were huge, they had massive components inside them that could withstand surges, and ultimately they lasted a long time (I can remember my parents having the same TV for 20+ years). TV’s built today are so thin, and they enable you to do so much more than just simply watch TV. These features mean the technology inside these TV’s has to be so much more sophisticated and faster. Technology in itself though is becoming smaller and more sophisticated, and most electrical equipment nowadays has very delicate micro-processor’s inside. These micro processor’s are very sensitive, especially to over-voltages (surges). The surges prematurely degrade these components, which leads to device failure.


In a domestic situation, this means expensive equipment having to be replaced more often than is necessary.


A Typical TV from the 1980’s 











Compared to a TV from 2019











Add up the value of the electrical equipment in your house and you make your own mind up if it’s worth protecting it all for about £60.


Please be aware that the SY2-D is a Surge Protection Device, not a Lightning Device. This means it will not protect your electrical equipment against direct Lightning strikes. You only need to install a combined Lightning & Surge Device if the domestic property is fed directly by overhead power lines, or it has an external lightning protection system on the building (copper tape and earth rods). To read more about Lightning Protection in Domestic installations please look out for our next article, which will be released next week.


To view the technical specifications or purchase the SY2-D please follow this link:

How to choose an SPD

Due to the changes in the 18th edition there has been the sudden appearance of many surge protection experts, so as a company with over 50 years of experience in the surge protection industry, the technical team at Surge Protection Devices Ltd would like to give you some pointers on how to choose an Surge Protection Device (SPD) for your installation.

Types of Protection

When discussing different types of surge protection, there are three main types:

Type What it does Where to use it
Type 1 Protection against direct  Lightning strikes At the mains incomer of any electrical installation where external Lightning Protection is installed, or is fed by overhead lines.
Type 2 Surge Protection At the mains incomer of any building that doesn’t need any lightning protection, and for use on any sub boards more than 10-15 meters from the main panel.
Type 3 End equipment protection On any piece of equipment where a low let through voltage is needed.

The types of surge protection are combined in most units, giving you two main types. Lightning Protection or Surge Protection.

What are we protecting against?

For the majority of installations we are protecting against surges. A surge is a voltage spike, these are very short elevations in the voltage supplying electrical equipment. Surges can be caused by quite a few different factors, such as switching events. In a domestic property this could mean switching on your washing machine, or commercially, all of the computers in an office being turned on at the same time when staff arrive for work, and industrially, generators or machinery that uses a high level of power when turning on. Nearby lightning strikes can also cause surges in the system as lightning can travel a long distance underground interfering with electrical equipment up to 2 miles away. So in most cases we are looking at a type 2 on the main incomer and type 2 on any subsequent sub boards.

What about lightning?

The only time that a direct lightning strike becomes a consideration is if the         building has either an external lightning protection system, or if the building is fed directly by over head power lines. In these two considerations both will cause a lighting strike to be transmitted directly on to the incoming panel of an installation. In these cases we would be looking at a type 1 device on the main incomer and type 2 on any subsequent sub boards.

How surge protection works

When a surge is detected by an SPD, the excess voltage is diverted to earth. The device then resets itself and is ready for the next surge. This whole process takes place in about 25 nano-seconds, so is extremely fast. The supply to the rest of the installation is never disrupted, as its only the over voltage which will be diverted to earth.

How to choose a device

Ok, so now we know what type of surge protection we need, now we need to consider which device. The most important things to consider are:

Is the device suitable for your earthing arrangement?
This is one of the most common issues with SPD installation. The most important consideration is for TT systems, where the device needs to be suitable. Surge Protection Devices LTD provide Devices suitable for every earthing arrangement, and are happy to assist in choosing the correct device for your installation

Is the device protecting both the live & neutral poles?
There are a few devices on the market with may seem inexpensive compared to other devices, but if the device is not protecting both live & neutral, surges may enter your property and bypass the SPD.

What warranty does the manufacturer provide?
This is generally a key indicator of the quality of the components used in the SPD. Surge Protection Devices LTD provide a 10 year warranty with all of our products

Do you feel confident that the manufacturer could assist with any technical information you may need?
With surge protection, you may require some additional information to complete your installation. You will need to have confidence in the manufacturer of the SPD to ensure they can help assist you. Surge Protection Devices LTD are the leading manufacturers of surge protection devices, we have been supporting customers in the U.K. market for many years. We work with leading training organisations to hold seminars around the country to expand the knowledge of surge protection and we also sit on the JPEL panel to aid in the production of the latest regulations.

Is the device from a trusted source?
Are you buying from a reputable wholesaler or distributor? Surge Protection Devices LTD have national accounts with all of the major Wholesalers in the UK, and we also work with many Independent Wholesalers to ensure you are provided with the correct information when you purchase your device.

For more information on any of the devices or would like to discuss your installation further, please give us a call in the office on 01484 851747, or visit our website