In my opinion, the report appears to suffer from logical and empirical shortcomings in its claims and support. I wonder if the report may be applying a different standard and test waveform than the one that the Furse M1 devices are based on and evaluated against, and it may be overlooking the integrated and improved protection that the Furse M1 devices provide. The report also fails to present a lucid and thorough examination of the current division concept and the anticipated surge currents for the site.

If you could attach or link to a copy of the report you have concerns about, we may be able to comment

Mike

Thank you for your reply, mapj1. I have summarised the main points of the report in the original post. The report is actually an email that criticises the current SPDs and urges their immediate replacement. My question is whether we should challenge this recommendation or comply with it at a potentially high expense.

Can you explain what the significance is of the diagrams and table extract you have posted ? Are these the aspects you have issue with and why?

Note that SPDs at the origin of an electrical installation are most unlikely to survive a serious direct strike to the building with or without an LPS, though in operation they may reduce the damage to  some of the content, in a facility that has to survive at least a fairly  significant strike, at the point where the LPS and the normal wiring meet, there would be arrestors tested with a longer duration (350us ) test waveform, rather than the 8/20 waveform used to test smaller devices.

They are however most use at clamping the surges that reach them due to strikes  on other  buildings/overhead lines/nearby ground,

Generally it is not resistance but inductance that decides how real lightning impulses are divided between multiple paths, and really silly things like hairpin bends that would have no effect at DC or 50Hz can completely alter the lighting induced waveform,

Real lightning waveforms are very variable and a long way from any of the lab test waveforms used to verify that kit will survive surges, or to test surge arrestors. The test waveforms are defined so they are easily recreated with charged capacitors, resistors and fast acting contacts or semiconductor switches.

The dehn guide is quite a good introduction to the topic, though not a light read.

Mike,

Thanks mapj1. The table is showing LPL & LPS class 3/4 (12.5 kA per mode) I can confirm that there are multiple services therefore the current should split further (shown in diagram 2),  so our installation is classed as LPL/LPS 3/4. So the argument is there is no requirement to replace the existing SPDs for 25 kA per mode type to meet LPL/LPS class 1. 

What are your thoughts mapj1 on the immediacy required for the replacement of the existing Surge Protection Devices (SPDs). Quick recap, the current infrastructure comprises Type 1 SPDs, multiple transformers, switch rooms, and bonded extraneous conductive parts, aligning with a Class 4 categorisation shown above. I hold the view that the urgency for such replacements is not paramount at this time. Your insights on this matter would be highly valued, cheers. 

gkenyon, I am reaching out to request your assistance, leveraging your esteemed engineering expertise. Your professional guidance would be greatly appreciated.