TN-s if it really is TN-s will be fine.
The problem is that a lot of services that present as TN-s are really TNC-s, or at least have some of the risks of it, as additions and repairs to the DNO network occur , and often in the new wiring neutral and earth are combined.

TNC derived supplies can be more problematic, as there can be a voltage offset between the true ground (the stuff you stand on) and the earth in the sense of the CPC of the appliance.

Wet concrete is not a great insulator, better but not a lot better than bare earth, but equally, the fact this is a class 2 device means you wont be grabbing the CPC and standing well connected to the terra-firma earth at the same time, which is the real risk of tingles.

So  to the SELV lights - if they are SELV, they should be fine, as SELV implies Extra Low Voltage  ( 50VAC/120VDC or 50VAC 75VDC depending on your choice of international standards. ) and double or reinforced insulation between the Extra low voltage output and the Low voltage (Mains input). That said, the term is falling out of favour as it does not align well with how modern electronic supplies are made and then graded.
The regs also allow AC lights at 12V  that are not really SELV as an alternative, but the preferred lighting  for Zone 1 is indeed SELV. The switches that operate it need to be further into the dry  zone though if carrying mains.

EDIT having read other answers, and re-read this one, and apologies my initial reading of the regs was not correct - ignore the above. As it is potentially misleading, I have now struck it through.

I assume the IET guidance you refer to is similar to this wiring matters 2021 article, but if you have not seen it as well, then  this older but more wordy article is perhaps more comprehensive.

Mike.

TN-s if it really is TN-s will be fine.
The problem is that a lot of services that present as TN-s are really TNC-s, or at least have some of the risks of it, as additions and repairs to the DNO network occur , and often in the new wiring neutral and earth are combined.

TNC derived supplies can be more problematic, as there can be a voltage offset between the true ground (the stuff you stand on) and the earth in the sense of the CPC of the appliance.

Wet concrete is not a great insulator, better but not a lot better than bare earth, but equally, the fact this is a class 2 device means you wont be grabbing the CPC and standing well connected to the terra-firma earth at the same time, which is the real risk of tingles.

So  to the SELV lights - if they are SELV, they should be fine, as SELV implies Extra Low Voltage  ( 50VAC/120VDC or 50VAC 75VDC depending on your choice of international standards. ) and double or reinforced insulation between the Extra low voltage output and the Low voltage (Mains input). That said, the term is falling out of favour as it does not align well with how modern electronic supplies are made and then graded.
The regs also allow AC lights at 12V  that are not really SELV as an alternative, but the preferred lighting  for Zone 1 is indeed SELV. The switches that operate it need to be further into the dry  zone though if carrying mains.

EDIT having read other answers, and re-read this one, and apologies my initial reading of the regs was not correct - ignore the above. As it is potentially misleading, I have now struck it through.

I assume the IET guidance you refer to is similar to this wiring matters 2021 article, but if you have not seen it as well, then  this older but more wordy article is perhaps more comprehensive.

Mike.

mapj1 said:

The regs also allow AC lights at 12V  that are not really SELV as an alternative,

I don't believe that's the case for Zones 0, 1 and 2 for a Section 702 location (702.414.3 prohibits "non-SELV/PELV" conformant electronic sources). Recommend to check with the manufacturer that the supply is actually SELV (at the appropriate voltage limits, see below).

Similar prohibition on sources to 413.3(iv) apply in Sections 701, 703, 706, and 710.

The reason for this prohibition, is that some product standards do not conform to BS EN 61140, and permit, in some fault conditions, the touch-voltage to rise above that above the relevant voltage limit for the location (or 50 V AC/120 V DC in general), and the touch-current to exceed that available from a suitable isolating transformer. Some product standards base this on the risk of the product being in dry locations (which, for example, the PSU may be) but don't consider the power from the product may be used in a 'special location'.

mapj1 said:

So  to the SELV lights - if they are SELV, they should be fine, as SELV implies Extra Low Voltage  ( 50VAC/120VDC or 50VAC 75VDC depending on your choice of international standards. )

And again, in Zone 0 of a Section 702 is limited to 12 V AC/30 V DC, and Zone 1 limited to 25 V AC/60 V DC (702.410.3.4.1).

Zone 1 extends 2 m from the edge of Zone 0, so in that case appears as the lights may be in Zone 1, so the 70 V DC is a problem.

That makes far more sense. Ignore my previous answer as complete bull based on misreading the advice.

M