Fine, in my view, presuming that the cables within are insulated and sheathed. Not suitable for PVC singles in my view.

If reasonably near a socket outlet, then in my view the likely presence of cables within is obvious.

Forgot to mention, T&E, visible at the DB end

I'd say it was concealed on a wall, not concealed in a wall - so 522.6.202 etc don't apply. So yes, in effect, it's decorative timber trunking. In essence no difference to those PVC trunking systems that pretend to be cornice or dado or skirting boards.

   - Andy.

AJJewsbury
I'd say it was concealed on a wall, not concealed in a wall - so 522.6.202 etc don't apply. So yes, in effect, it's decorative timber trunking. In essence no difference to those PVC trunking systems that pretend to be cornice or dado or skirting boards.

I'm not sure it is classified as trunking, or any other kind of recognised cable containment, because it doesn't comply with the relevant standards.


It's basically building/construction materials, and the cables are concealed behind them.


So, I think I'd agree the cables are not concealed in a wall or ceiling, and I don't think it's difficult to deduce where the cables are.


At the end of the day, it's far better than the cable being stuffed inside the wall with whatever insulation is there ...



But what strikes me as a relevant discussion point, is .... What is the Installation Method [in Table 4D5]?


OK, even if we choose Method 103, it's still not a massive problem for a 32 A RFC in 2.5 sq mm, ref Table 7.1(i), p65 of OSG, but suppose someone is reading this in the future, planning something similar for another application ... and I apologise in advance if no-one else is intrigued by the question.

cooling will compare to any other unvented duct of similar dimensions. You cannot reasonably expect the regs to have a special section for it - just occasionally folk have to be a bit cleverer than thumbing through the tables.

Thanks for the replies. I cant help thinking 102 might be more fitting than 103, the "trunking" has actually been routed out with a void about twice the volume of the cable so cable would be touching wall or covered with air. Valid point though as winter use could load the circuit up with heaters. 25A MCB might be a good idea.

I agree the wooden structure won't comply with standards for trunking - I was just trying to say in terms of concealment is has the same effect.


No thermal insulation involved - so no need to resort to the 100 methods.


There is a method for cables in wooden mouldings - 12 - but oddly only for unsheathed cables. I guess 40 is the closest for sheathed cables - so reference method B. 4D5 doesn't mention method B, so revert to the generic 4D2A table where 2.5mm² gets a 23A rating.


   - Andy.

Andy, the exact 2 methods I was looking at last night, 12 and 40. Its a good point though to use table 4D2, a T&E is also just a plain ol multicore cable as well as a 'insulated and sheathed flat cable'

Ref the "Safe Zone" issue.

In theory we stick to safe zones to reduce the risk of careless damage.

We work on the principle that eveone knows/should know where cables are likely to be when hidden from sight.

Of course we all know that lots of people are not aware of this - Ok they should not be risking accindental penetration if they are not competent but we know that in practice this does happen.

So we does our best.

Is it reasonable for us to assume that a "reasonable person" might reasonably deduce that this is trunking to contain and protect cables and therefore we must keep away with nails/screws and the like?

Methinks probably it is not or not much less safe than burying in walls or than using "recognised" trunking therefore nearly as good as using "proper" trunking.

If we use this method then inevitably some accidents will occour, however we also carry almost the same risk with our bog standard methods of zoning and trunking.and the risks are not totally eliminated.

The real reason I raised the question about 4D5 was not to question whether a B32 is OK for this circuit or not - simply that I come across a lot of applications in which T&E is used, that aren't covered in 4D5 - causing a lot of debate about what to do next, or which method or other table is easier to use.


And of course I see training materials from different organisations with different approaches to that problem too ... so for example if one organisation chooses to well over-engineer and select Method 103 (13.5 A for 2.5/1.5 cable), they will get a vastly different answer to someone using Method 102 (21 A for 2.5/1.5 cable).


In reality, I think this is probably nearer to Method B as Andy alluded to.


However, how valid is it to use another table like Andy did? Let's have a look (apologies if this is teaching people to suck eggs, just thought it would be useful to readers in the future) ...

 

csa

Current carrying capacity

Ref Method C

Ref Method A

2.5 mm2 Table 4D2A

27.0 A

18.5 A

2.5 mm2 Table 4D5

27.0 A

20.0 A

In the table above, we see that clipped direct (Method C), both the 4D5 and 4D2A show the same current carrying capacity. However, when enclosed in a conduit in a thermally insulated wall (Method A), 4D2A round cable has a 7.5 % lower current carrying capacity than 4D5 T&E. This is because it's radiating surface area is less for the round cable.


So, Andy's approach of using 4D2A is no less safe than using 4D5 - it certainly errs on the side of caution, as the table above demonstrates ... but it's taken an extra couple of steps to see that.