The heating elements are presumably not strictly  in the zones, but below the top finish of or within  the floor beneath. Even so I think you need the kind where the element has an earthed jacket/ foil or mesh between the element and anything which if wet could cause an issue.

 Controls and any associated accessible wiring need to be in Zone 2 or ideally  further out.

Mike.

Thanks for your reply Mike, I am grateful for you taking your time to respond. ️

But of course there is an argument regarding equipment embedded beneath zone 0 but as grout is purous think this would be strongly challenged by building control ;)

alas I need absolute clarity on the 18th Edition rules, the given the Warmup heating cables are sheathed with earth as specified under Chapter 701.753 however under this chapter it makes no mention of zones... so really it can be argued that as such it can be placed in zone 0 as long as it is IPX7 rated as per 701.512.2 (i):

701.753 Electric floor heating systems

For electric floor heating systems, only heating cables according to relevant product standards or thin sheet flexible heating elements according to the relevant equipment standard shall be erected provided that they have either a metal sheath or a metal enclosure or a fine mesh metallic grid. The fine mesh metallic grid, metal sheath or metal enclosure shall be connected to the protective conductor of the supply circuit. Compliance with the latter requirement is not required if the protective measure SELV is provided for the floor heating system.

But here you can clearly see Warmup think it appropriate to place this 240v cabling in Zone 0, I believe even under the floor you are still in zone 0 alas.

https://www.warmup.com/warmupedia/questions/can-warmup-electric-heating-installed-shower here makes mention of must be install between 2 non combustible materials though I don't see this in the regs under Bathroom section

here they show the electric cabling in Zone 0 before tiling  https://support.warmup.co.uk/questions/installation/can-warmup-electric-heating-installed-shower/

I'd worry  about  zone 0 - that is normally taken as being inside the bath tub or shower tray Underneath   a one piece tray or tub it is normally taken as outside the zones.

having said so that is a photo where they are going to tile over it to make the shower floor in sections would worry me a bit.. Does it have an earthed sheath braided over the elements ?.If it does, the way I read it you are OK.

Mike

Thank Mike

Here is the context I should have stated with, I intend to instal a wet room where the shower tray is a tiled floor over a wet room former https://www.heatandplumb.com/acatalog/impey-aqua-dec-linear-wet-room-former-ad3l1590 so no actual visible tray, so only thing between the person and the cabling in places is flexible grout between porcelain titles 

The heating wire is earth sheathed braided yes: https://www.warmup.co.uk/underfloor-heating/electric/cables/loose-wire

And yes makes me nervous putting this un the tiles in the shower, but everywhere I look online specifically those that sell heating cable state you can put in the shower... the idea is great toasty feet when you get in but the possibility of electric shock I take extremely seriously and I work in absolutes so I won't take a Salespersons word for it their product can be used in this way... thought 18th Edition would be a little clearer here, think the 17th Edition was clear as far as I can remember but as much has now been integrated its become murky... I should I suppose air on the side of caution, but Im a kind of person that really wants to know from the horses mouth and if it says Ney then OK ;)

Chapter 701.753 however under this chapter it makes no mention of zones...

Indeed - therefore the usual interpretation would be that the regulation therefore applies without regard to zones - so equally for the whole location.

The live conductors of the UFH will be fully insulated, covered with an earthed conductive mesh, sheathed and protected by 30mA RCD as well as normal ADS - so the chances of receiving a fatal shock seem pretty miniscule. The earthed braid will act as supplementary bonding for the floor area, so even if the cable were sufficiently damaged to let water get to the conductors, you'd need both a broken c.p.c. and simultaneously a failed and the RCD for the dangerous voltage to persist and even then it would still be almost impossible to generate a potential difference between two different parts of the floor area - you'd need something else earthed and within reach to complete the circuit.

Compared with say a typical electric shower (bare conductors in an unsealed plastic box, on a 30A+ protective device and for many years not even a requirement for an RCD) the UFH requirements seem rather strict.

   - Andy.

Ahh a wet room is not really a bathroom - no bath, and the 'zones' are not defined the same way, Even so, if your heaters are inside an earthed braid or similar, and it sound like they are, then even it it ever becomes wet, you are only getting feet to earth potential, so that is deemed OK, after all it is OK to have exposed pipes connected to mains earth.

Mike

Turn of Phrase, I use Bathroom interchangeable as Shower Room given they both have zone 0.1 in, I was undecided wether to go Wet Room OR Shower Room.

But you are valid in what you say as there is a clear distinction between Wet Room and Bathroom in terms of Zones but as both share a  zone 0 I felt the distinction was not required in my earlier question, either way Im going into zone 0 "The Danger Zone" just call me Mavric entering into this zone ;)

Thanks for your input, highly valued, Best, Jason 

Turn of Phrase, I use Bathroom interchangeable as Shower Room given they both have zone 0.1 in, I was undecided wether to go Wet Room OR Shower Room.

But you are valid in what you say as there is a clear distinction between Wet Room and Bathroom in terms of Zones but as both share a  zone 0 I felt the distinction was not required in my earlier question, either way Im going into zone 0 "The Danger Zone" just call me Mavric entering into this zone ;)

Thanks for your input, highly valued, Best, Jason