Skip to main content
Peter E
Super User
Peter ESuper User
Super User
September 10, 2026

Protecting an EV and Charge Point with an Surge Protection Device (SPD)

  • September 10, 2026
  • 4 replies
  • 27 views

Outside your house you have an EV and a Charge Point connected to the mains. These items have a considerable value but are subject to mains voltage spikes from time to time. Most of the time the voltage spikes can be handled by the equipment as they have their own limited protection but, just occasionally, you will get the odd damaging spike caused by lightning or a power supply event (outage/restoration).

 

In order to protect your EV/CP and also other equipment in your house you can fit a Surge Protection Device with a current capability of 40kA (40,000A). For most of the time it doesn’t do anything but it is capable of significantly reducing anomalous power spikes that occur from time to time. There would be a cost to having one of these fitted but consider it as an insurance policy. You might not ever need it but it could prevent a lot of damage to expensive equipment if you did get a large voltage spike for some reason.

 

 

This shows a typical arrangement of an SPD within a consumer unit (not mine). The incoming mains isolation switch is on the right followed by an MCB (1) and then the SPD (2). There is some discussion about whether you need to fit an MCB before the SPD but the consensus is that if your incoming DNO fuse is 80 or 100A then an MCB is required. If you are on a looped supply, or otherwise, and your fuse is 60A then not fitting an MCB is considered to be OK.

 

You might think the MCB would ‘pop’ (go open circuit) when a surge is clamped but it doesn’t as the event happens so quickly it doesn’t have enough time to react. However, if the SPD clamps a surge bigger than it is capable of surviving, and it goes short circuit as a result, then the MCB will open the circuit quicker than an 80/100A fuse would blow. However, it’s considered that a 60A fuse would blow quicker than the MCB would react so the MCB is not needed for that size of fuse. I have a 60A fuse so my SPD doesn’t have the MCB protection which is why I’ve not shown it. If the SPD has clamped more spikes beyond its rating then the green window on the device turns to red and it needs to be replaced. It’s also showing that it’s doing its job.

 

For EICR checks you can’t have an SPD in circuit and it would have to be temporarily disconnected for the insulation check.

 

A Youtube video from eFixx

https://www.youtube.com/watch?v=L29mgEw02NY&t=390s

 

    4 replies

    Chris_OVO
    Community Manager
    Chris_OVO
    Community Manager
    September 10, 2026

    Hey ​@Peter E,

     

    I really appreciate you sharing this! It's not something I would have thought of on my own and i’m sure others will find it helpful.

     

    Thank you!

    Renewable energy jokes never get old.
      Peter E
      Super User
      Peter ESuper UserAuthor
      Super User
      September 10, 2026

      Hi ​@Chris_OVO 

       

      It's one of those ‘hidden’ items that never get talked about because they do nothing most of the time and nothing happens (fortunately) if you do get a damaging power spike. I looked for the subject on here and found that there was no mention of it so ‘put pen to paper’ so to speak.

       

      A long time ago as an electronics design engineer I was tasked to produce a design modification for a flap controller on an aircraft to make it proof against lightning strikes. I did that and it passed all the tests first time (because I followed all the design rules) so lightning protection became one of my skills. I also used a similar method on the railway and that was very successful as well. This is a similar subject and an SPD works in the same way. Time to publish!

       

       

      Reducing my yearly fossil fuel usage with an EV (-900 litres petrol saving about £950/year), A2AHP (-8,700 kWh gas, cost neutral) and Timed Immersion heater (-1,500 kWh gas, £20/year more expensive but reducing as the gas price goes up)
        BPLightlog
        Super User
        BPLightlogSuper User
        Super User
        September 10, 2026

        I was offered an SPD on my recent EV charge point install - I actually declined.

        SPD’s have been used in several countries for a while but are fairly recent introductions to the UK.

        Most electrical and electronic devices have to have a level of protection built into their supply circuitry as part of International (& British) standards but an additional layer of protection can be desirable of course and - as you mention ​@Peter E - can be thought of as insurance.

        As part of my former role in the test & measurement industry, one thing I was less sure about was the inability to test/check an SPD as you can with an RCD/RCBO or MCB. Some do now offer a device to perform a test but as many have mentioned, any test on an SPD involves a voltage injected into the device which can in fact derate its capabilities, which of course is not useful.

        Bring me Sunshine ~ E&E {Solar PV, Battery Storage, Hybrid EV, ASHP and Home Assistant automation}
          Rank 6
          Nealeb
          Rank 6
          September 10, 2026

          When my EV charger was installed, it included an SPD and MCB in the meter cupboard - the feed comes directly off the meter. I hadn’t heard of them in this context either and I wasn’t asked if I wanted it. But as it was part of the standard install, I wouldn’t have refused anyway!

            Terms & ConditionsAccessibility statement

            OVO Energy Ltd, Floor 5, Crescent, Temple Back, Redcliffe, BS1 6EZ, (Company no. 06890795) registered in England and Wales.

            OVO (S) Gas Limited is registered in England and Wales (Company No. 02716495) at Floor 5, Crescent, Temple Back, Redcliffe, BS1 6EZ.

            OVO (S) Gas Limited is part of OVO Group Ltd