Thanks everyone for sharing your thoughts on this; I think Graham is correct in suggesting that it probably isn’t a problem worth worrying about.

It has, however, prompted me to step back and consider just what section 443 is trying to achieve. 440.1 States that the requirements are intended to provide for the safety of electrical installations in the event of voltage disturbances. However, what aspect of safety is being considered given that protection against electric shock or thermal effects are addressed elsewhere? 443.1.1 Deals with protection of electrical installations against transient overvoltages of atmospheric origin or generated by the equipment within the installation, and 443.6.1 states that “Overvoltage categories are defined within electrical installations for the purpose of insulation coordination…” and provides Rated impulse voltages for equipment selected according to the nominal voltage to distinguish different levels of availability of equipment with regard to continuity of service and an acceptable risk of failure.

So, aside from the direct effects of a lightning strike or the consequences for any safety critical systems reliant upon the installation, is 443 really about reliability / availability rather than safety? Should we be interpreting it as guidance for the designer when choosing components or the need for surge protection devices, rather than a clear requirement that all equipment in the fixed installation must be rated for category III? If the latter was the intent, then we need to study a lot of product standards. The examples of Overvoltage category III equipment given in Table 443.2 include distribution boards, switches and socket-outlets, and the 17^th edition of the regulations included wiring systems in this list; manufacturer’s data for distribution equipment does commonly state the overvoltage category but I struggle to find that information for a socket outlet or a cable. I’m sure that the relevant product standards would reveal all; unfortunately, since retiring, I no longer have ready access to those. Wago do publish relevant information on their web site but I found it somewhat unclear, hence the original post.

Anyway, I’ve waffled on enough about something that probably isn’t a problem at all; I do still wonder about 443 though, requirement or guidance?

Geoff

Geoff Lyons said:

I struggle to find that information for a socket outlet or a cable

Cable you won't find.

Socket-outlets to BS 1363-2 used for fixed wiring (but not rewirable "free" socket-outlets etc.) have an impulse withstand test as part of the standard, and the standard itself states Overvoltage Category III.

For industrial outlets, BS EN IEC 60309-1:2022 states 'overvoltage Category II' (Clause 21.1.6)

That's useful to know, thanks Graham.

That's useful to know, thanks Graham.