well if you have earthed steel conduit, regs wise you are fine pretty much where ever you run it, and if it is ever drilled it can be re-threaded. Over a very long straight length you may need a larger diameter then first expected to be truly re-threadable.

In your shoes I'd still aim near to be near but not quite in an internal corner where things are less likely to be casually screwed to the wall.  Or outside behind the drain pipes assuming it has some of those ;-)
Mike.

Thanks Mike. What would be the merit in earthing the conduit?

 "Or outside behind the drain pipes assuming it has some of those ;-)" until replacement drainpipe fitted just slightly off the original course of fixing brackets 

Any voltage arising that might otherwise give an earthed person a shock when they drill into the cable - let's assume sun is shining, is mitigated by that current flowing mainly in the earthed conduit instead. The hapless driller is then holding a drill at or near earth potential rather than at DC voltage unknown.

Who knows it may even fire some kind of ADS, but probably not very fast as the solar strings are current limited by nature.

Without knowing the PV panel size, some knock out a few hundred volts as a series string and deserve commensurate respect.
(For example the "sunny boy" series of  inverters expect 100-600V input to allow use of strings of 5-10 panels of varying sizes. 1 panel may be 30-60V  depending on the design.)

Do not forget you will need to earth the solar panel frames - or at least most makers now recommend that.

Mike

I would have expected the DC output of the panels to be isolated from ground, in which case accidentally drilling into one wouldn't be immediately dangerous.

You may find that the inverter would spot a short to ground as part of its power-up self-test, though.

It's common for the frame holding the panels to be earthed.  Do you know if it's being done here, and if so has anyone thought where that earth wire is coming from?

Earthing the conduit wouldn't provide ADS - so you can't rely on that for shock protection from penetration by nails etc - so the steel would have to provide protection by purely mechanical means (and the wiring inside to meet double/reinforced insulation requirements - e.g. insulated & sheathed, not just ordinary singles) (presuming it's not SELV/PELV.) Whether steel conduit provides sufficient mechanical protection from the likes of paslode type nail guns, is perhaps the question.

   - Andy.

it does not need to provide rapid ADS, it just needs to ensure the drill bit is earthed, and provide a bonding like return to earth path - same thinking as the old bathroom bonding without the fast acting RCD.

On transformer-less inverters the strings alternate between being one way across the mains and then the other at 50Hz, with some wave shaping electronics and/ or with symmetric filtering - like this.  Note that  as the H bridge transistors switch  alternately, the mains live is routed to one side of the PV array or the other so the DC polarity is always correct.

Simplified transformer-less inverter control electronics not shown - the side of the AC shown as  'earthy' is the neutral.

The ones with  a high frequency transformer, rectifier and then 50Hz commutation may fully float the PV strings relative to earth or may earth one side of the DC  for EMC reasons.

HF transformer kind - to left the DC from the panel is made into a supersonic square wave and transformed up or down and then rectified. The rest of the design is as per the transformer-less one above.

Mike.

Coming back to the Sunny Boy ones, on at least one common model they do say to earth negative side of the string, which makes the positive side an immediate shock risk during the day.

Caution on cutting vertical chases, Building Regs Part A Structure 2C30

"Chases:

a) vertical chases should not be deeper than 1/3 of the wall thickness or, in cavity walls, 1/3 the thickness of the leaf

b) horizontal chases should not be deeper than 1/6 the thickness of the leaf of the wall

c) chases should not be so positioned as to impair the stability of the wall, particularly where hollow blocks are used."

if anywhere near these dimensions, check with architect/structural engineer. You wouldn't want 40+ claims on your insurance

I would be happier with there being a dedicated service duct with the conduit running up through it.

We at the point in time when all new homes need a plant room and service ducts rather than equipment such as inverters and storage batteries being shoved in lofts and cables being dangled here, there and everywhere.

it does not need to provide rapid ADS, it just needs to ensure the drill bit is earthed, and provide a bonding like return to earth path - same thinking as the old bathroom bonding without the fast acting RCD.

Going down the section 419 route then? (to meet BS 7671 requirements) Wouldn't that then also require supplementary bonding to everything within reach of the conduit (or drill)?

   - Andy.