Getting some CPD with the Dehn Academy

This week I popped down to West Yorkshire to get some CPD on overvoltage protection and I thought I would write this little blog to explain why I chose to go, why I chose Dehn as my provider, what I learnt, and what reflections I have made on the days training.

First of all, if you are wondering why I choose to do CPD, then check out this article

Why I chose to go?

I am not a lightning engineer, and I am rarely on the tools these days other than inspection and auditing work. But I am a consultant and I deliver electrical training so it is always important to identify weaknesses in my knowledge and/or resources that will help strengthen and improve my professional development.

The subject of overvoltage protection has in my experience often been skipped or overlooked in the training room and the introduction of new regulations making the selection of overvoltage protective devices, such as SPDs, more apparent and have confused the matter even further.

I registered on a one day course titled 'BS7671 18th Edition Wiring Regulations & the requirement for SPD’s'.

Why Dehn Academy?

Trusting Dehn for quality training wasn't something that I needed convincing to be honest. Having worked within the e5 group I have hosted podcasts with the technical team at Dehn, who sit on technical committess etc, and I knew even if the same persons weren't delivering the training, they would at least be involved in the training and quality assurance.

What did we cover?

The course went through the requirements of sections 443 and 534. I was able to ask many questions to get a deeper understanding on why certain things were written within these sections and where they originated from. This is excellent for me as I can improve my own training to candidates on the regulations training by adding this extra information and keep the training levelling up.

For example the CRL risk assessment, whilst I knew that LPAL meant overground and LPCL meant underground, I now know the 'A' means 'arial' and 'C' means 'covered'. Little things like this will get asked of me on courses all the time.

Also that the High Voltage part of the LPAL calculation uses 0.2 and 0.4 as deration factors due to the transformer between HV and LV.

We delved into the definitions of Rural and Suburban environments and identified that this factor is the greatest significance in the risk assessment outcome, and that many engineers deliberately misuse this factor to result in SPDs not being necessary.

It was also discussed that only the consumer unit in a domestic installation is likely to be LPZ1 - as it is metal and shielded.

The conneciton of CT1 is for TN systems only, whilst TT systems require CT2. The reason for this is that there is a different component in the neutral on the CT2 which prevents leakage currents and therefore avoids operating RCDs. Devices that declare themselves suitable for both earthing systems are CT2.

The restrictions for the length to be 10 m is due to addiditive inductive effect occuring within the cable with length. As the cable is acting as an indutor then the voltage will climb. Ideal solution is to consider a total Up of 2.5kV which is achieved by a 1.5kV SPD and 1kV inductive effect within the short conductors.

The differences between varistors and spark gaps, expanding on why spark gaps are most suited for type 1 SPDs.

  • Decoupling with multiple varistors and the risks of using differnet manufacturers.
  • Short circuit current and follow up current.
  • lengths of connecting conductors
  • with an 8/20 device, that every additional metre can add 1 kV


I have taken so much away from my days training with Dehn. I will be amending my training on sections 443 and 534 to improve the quality of SparkyNinja's 18th edition training and I will also be adding some inspection considerations to the 2391 periodic inspection course.

For example:

  • SPD suitability with growth of an organisation over time, repeat inspections under BS 62305 may or may not have been carreid out
  • The correct risk assessment carried out
  • The need to request a lightning protection risk assessment, to then determine the adequacy of proteciton on electrical equipment that may be installed outside of any lightning protection boundary
  • The potential for plant or solar panels to be installed and bonded to a lightning protection systems and wether this has been considered as a risk wioth regards to maintenance on stormy days
  • If no SPD is instaled, consider the assessment of the local community to determine if lightning protection systems have been erected on any new or existing buildings within a 2 km radius of the installation


I will be returning to Dehn Academy after the second amendment of BS 7671 is released to update this training and I will also be registering on their technical courses on BSEN 62305 1-4.

This will be an opportunity for me to improve my understanding on these technical documents whilst at the same time reflecting on any improvements I can make on my design and inspection and testing training.

You can check out Dehn Academy here: Dehn Academy