In my view threaded conduit is fine, and is arguably one of the best wiring systems for many applications.

I do not consider that properly installed threaded conduit contravenes the requirement for joints and connections to be available for inspection. Such joints and connections should only be made at accessories (remove the front to inspect) or at conduit boxes, adaptable boxes and similar fittings (remove the lid to inspect). I have seen conduit installations with soldered and tape insulated joints concealed along a conduit run. This is undoubtedly poor practice and is prohibited, and in my view is still prohibited even  with non threaded conduit which can not realistically be dismantled once the wall has been completed and surfaced.

Soldering wires is not so much the problem, more the fact that basic PVC tape loses its stickiness after a bit and comes unwrapped,. Self amalgamating tapes or even better hot glue-lined heatshrink are both far superior approaches to site applied insulation.  Better still, have the joints at the ends of the wire, and not in the middle !

Otherwise, as above, done well a threaded conduit is a great CPC though burying the joints in the plaster is not so clever and probably a stricn non-compliance, though of course it can be done with care, after all it is acceptable for gas pipes where the sealing requirement is greater ;-)  Be aware that galvanized steel, where the zinc has been cut away to form the threaded ends, is very vulnerable to corrosion, and should be protected in someway, especially outdoors. "Galvafroid"  zinc primer or epoxy paints are very both good options or if you want to undo it again, that horrible petrol smelling glass fibre tape that ruins your trousers.

I'd be less happy with 'grub screw' conduits, as there is more chance of it working loose and not being realised - a 2m length of pipe is not going to rotate half a dozen times under its own volition, and not be really obvious, but a small Allen head or cap head screw might, or the screw may miss the target if the pipe is not full seated.  Even more so, the joints really should not be buried, and that is doubly so for joints that are not all-round contact.

In the days of the 25A loop test, it was the slip joint and split tube conduit that was the most fun in terms of snap crackle and pop if things were not going to make it... Threaded stuff pretty much always managed just fine, except if there were loose bushes without star washers at the boxes.

Mike

This is one of those interpretation questions.

What type of wall are we considering? I would not bury galvanised conduit in a plaster wall, but would not object to it in a studding wall (or in a floor/ceiling void).

Neither "connection" nor "joint" is defined in Part 2.

Joints under the floorboards (be they galvanised conduit, in a Wago box, or an old-fashioned terminal box) may be inspected with a certain amount of bother.

I think it's another one of those situations where well established, tried and tested and almost universally accepted methods, don't quite align with wording of the regs. Certainly threaded steel conduit has been embedded into plaster and even concrete structures for as long as I can remember and unless it's corroded almost to the disintegration, continuity seems to be as reliable as any other method.

The conlok system I'd be more wary of - we used to have a "pin grip" conduit system (albeit with thin walled butt seamed enamelled conduit) in the days of cotton covered rubber wiring in domestics - and it was so reliable the regs specifically banned it for many years. I'm sure the modern grub screw systems are fine for surface use indoors, but personally I'd be wary of using it in embedded situations.

    - Andy.