Surge Protection Device (SPD)

bernardgreen said:

Why is "transient suppression" necessary ?

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All of those reasons, however it's not that equipment is poorly designed, it's an inevitable fact that electronic devices are easily damaged by high voltage transients.

What's changed is the quantity of electronic equipment in use, from very little to almost every electrical device.
The other significant change within devices is the type of power supply used - previously 50Hz transformers and linear regulators, now virtually everything is a high frequency switching supply, with silicon devices directly on the 230V input.

Some equipment may have transient suppressors installed, but they will be Type 3 at best, which will be of little to no use unless additional Type 2 or 1 is installed for the electrical installation as a whole.

This vid on 17:47. He shows an enclosure with a mainswitch incomer and the SPD in one neat unit. One of the comments mentioned removing the incomer on the CU, as there is new one in the SPD enclosure, so no sense in having two, to accommodate a couple of extra mcbs/RCBOs. To do this an extended bus bar is needed, however the 25mm or 16mm line cable would need to be lugged and attached to the bus bar by drilling it, attaching it via a nut and bolt with a shakeproof washer. I cannot think of any other way of doing it.

flameport said:

No.

It's either required or not.

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Wrong.....Yes you recommend that the client needs one BUT if the client says NO then you dont need to fit one.....It is only a Recommendation in a single dwelling not a requirement of the regs,you just make a note on cert that client didnt want one

markyd1 said:

It is only a Recommendation in a single dwelling not a requirement of the regs,

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The regulation:
View attachment 192327

Nothing about recommending.

A couple of ferrite cores threaded on the tails from meter to consumer unit are likely to be just as effective as a varistor in quenching fast transients

flameport said:

it's an inevitable fact that electronic devices are easily damaged by high voltage transients.

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Communication equipment can survive a lightning strike. Both when the strike is on the building where the equipment is and when the strike is on a building miles away but linked to the site with interconnecting comms cables.

But then general public would prefer to pay for cheaper devices with no protection than pay for an expensive item that is resilient.

flameport said:

The regulation:
View attachment 192327

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But it does mention single dwellings, dosen't mention transient under voltages which can be just as disruptive / damaging to non resilient equipment.

Has anyone mentioned that maybe the reason they should be fitted is to prevent transients generated at the premises from getting out into the local supply network.

flameport said:

The regulation:
View attachment 192327

Nothing about recommending.

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Yep. Similar to condensing boilers. They have to be fitted unless there is a valid reason not to.

flameport said:

All of those reasons, however it's not that equipment is poorly designed, it's an inevitable fact that electronic devices are easily damaged by high voltage transients. ... What's changed is the quantity of electronic equipment in use, from very little to almost every electrical device.

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That appears to be 'the thing to say', but I have to wonder how significant the 'risk' is. I've lived with what (particularly in the early decades) was probably an unusual amount of electronic equipment for 50+ years and, although it's impossible to be sure, have never experienced a failure which I had good reason to believe was due to voltage transients - even when. 'back then', many electronic components were much more 'fragile' than they are today.

flameport said:

The other significant change within devices is the type of power supply used - previously 50Hz transformers and linear regulators, now virtually everything is a high frequency switching supply, with silicon devices directly on the 230V input.

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True, but you again are talking about potential failure modes which I personally have rarely, if ever, encountered.

As you will be aware, I've been known to 'wonder about' the cost-effectiveness (in the broadest sense) of RCDs, but SPDs don't really have a significant 'safety' aspect (unless one really does some barrel-scraping) - so, whilst I have no problem with people fitting SPDs if they so wish, to make them a (default) 'requirement' seems (to me) to be even more questionable!

Kind Regards, John

I just had a Hager SPD fitted to my Hager consumer unit. They’ve just dropped the price of them from about £80 to £50 and the new version comes with a clever double pole din rail that connects to the screw rather than busbar terminals on the main switch.

One thing I’m struggling to understand though. So overvoltage is directed to earth (lots of videos online of this, of people running 500v insulation tests on them and seeing them drop resistance as they should) however what is the point of a neutral SPD (the Hager has separate live and neutral SPDs on a twin module base) on a TNC-S supply (ie much of the UK) since the earth will be exactly the same voltage as the neutral conductor?