Remove t&e sheaving for short conduit drops?

[Achillies]

Hi Again.

Yes I am "keen on the aesthetics of conduit" as I just think it looks the part for my workshop. I know it would have been quite a bit easier just to clip t&e to the wall but, whilst it may be a compliant solution, i think it looks poor. This way I have all the 2G boxes at eaxctly one height and all the saddle clamps exactly the same height ...very sad I know, but I like it!

My original concern was about cramming 2-off 2.5mm^2 T&e into one conduit as the MK 2 gang boxes I have bought only have one knock-out, and are fastened to the wall, though on closer inspection there is quite a bit of room. Don't forget the drops are only 800mm max.
The other issure was sealing the conduits against dirt and dust ingress, and I am not sure I have an answer other than add a blob of silicon.

Even know I don't fully appreciate why I shouldn't remove the sheave from the t&e as it still will be protected by the conduit.
If I do pass the t&e down the conduit I have gained 'triple' mechanical protection against an obvious loss of air gap.
What's the difference between baring back the sheaving for a short 800mm run and using singles throughout from the outset?

If I do bare back I guess I can use the conduit factors shown at http://www.tlc-direct.co.uk/Book/4.5.3.htm which shows i'm well in even if I count all 6 wires (2xL, 2xN, 2xE). i.e. 6x30 = 180 which is<460

 

[333rocky333]

either the regs or the osg suggest the sheaving of T+e should enter the accessory

 

[RF Lighting]

Just put both twins down the conduit as they are.

Every one does it and I've never heard of it causing a problem ever.

 

[ban-all-sheds]

http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=35138

 

[JohnW2]

If I do bare back I guess I can use the conduit factors shown at http://www.tlc-direct.co.uk/Book/4.5.3.htm which shows i'm well in even if I count all 6 wires (2xL, 2xN, 2xE). i.e. 6x30 = 180 which is<460

I think you have misunderstood. As I understand it, the material and calculations you are quoting relate to the capacity of conduit, in the sense of the number and sizes of cables that can be safely drawn into conduit of a certain size without risking physical damage of the cables.

That is totally different from the issue of the 'grouping factor' which has to be applied to current-carrying capacities when cables are 'grouped' (whether within conduit or anywhere else). Indeed, nearly all of this discussion has been based on the fact that grouped 2.5mm² cables (whether T&E or singles) within conduit would, after application of grouping factor, theoretically take the current-carrying-capacity down to less than the 20A minimum technically required by the regs for a ring final circuit. However, as several people have now intimated, many people would undoubtedly simply ignore this issue, particularly for such a short length of conduit/grouping as you are talking about.

Kind Regards, John.

 

[sparkwright]

Hi Again.

Yes I am "keen on the aesthetics of conduit" as I just think it looks the part for my workshop. I know it would have been quite a bit easier just to clip t&e to the wall but, whilst it may be a compliant solution, i think it looks poor. This way I have all the 2G boxes at eaxctly one height and all the saddle clamps exactly the same height ...very sad I know, but I like it!

My original concern was about cramming 2-off 2.5mm^2 T&e into one conduit as the MK 2 gang boxes I have bought only have one knock-out, and are fastened to the wall, though on closer inspection there is quite a bit of room. Don't forget the drops are only 800mm max.
The other issure was sealing the conduits against dirt and dust ingress, and I am not sure I have an answer other than add a blob of silicon.

Even know I don't fully appreciate why I shouldn't remove the sheave from the t&e as it still will be protected by the conduit.
If I do pass the t&e down the conduit I have gained 'triple' mechanical protection against an obvious loss of air gap.
What's the difference between baring back the sheaving for a short 800mm run and using singles throughout from the outset?

If I do bare back I guess I can use the conduit factors shown at http://www.tlc-direct.co.uk/Book/4.5.3.htm which shows i'm well in even if I count all 6 wires (2xL, 2xN, 2xE). i.e. 6x30 = 180 which is<460

To remove the sheath from the cables before putting in conduit is just crap.

You'll be making it harder for future alterations, will have a long bare earth wire which you'd probably have to sleeve, and just seems a mess.

Can't explain it, it's just not done.

 

[sparkwright]

In fact, you would have to sleeve the earths, as if the bare earths were to touch this could make fault finding difficult.

 

[JohnW2]

In fact, you would have to sleeve the earths, as if the bare earths were to touch this could make fault finding difficult.

True, but presumably no more difficult than if it were singles run in steel conduit and using the conduit as the CPC. However, I agree with you that what was being suggested is just 'not nice' (as well as unhelpful/unneccesary).

Kind Regards, John.

 

[Achillies]

If I do bare back I guess I can use the conduit factors shown at http://www.tlc-direct.co.uk/Book/4.5.3.htm which shows i'm well in even if I count all 6 wires (2xL, 2xN, 2xE). i.e. 6x30 = 180 which is<460

I think you have misunderstood. As I understand it, the material and calculations you are quoting relate to the capacity of conduit, in the sense of the number and sizes of cables that can be safely drawn into conduit of a certain size without risking physical damage of the cables.

That is totally different from the issue of the 'grouping factor' which has to be applied to current-carrying capacities when cables are 'grouped' (whether within conduit or anywhere else). Indeed, nearly all of this discussion has been based on the fact that grouped 2.5mm² cables (whether T&E or singles) within conduit would, after application of grouping factor, theoretically take the current-carrying-capacity down to less than the 20A minimum technically required by the regs for a ring final circuit. However, as several people have now intimated, many people would undoubtedly simply ignore this issue, particularly for such a short length of conduit/grouping as you are talking about.

Kind Regards, John.

Yes, you are right. The factor I was looking at was just a safe physical limit to how many cables could be drawn into a conduit.
I can now see why it makes no odds whether the cables were sheaved or singles as, if we consider all may be touching, then the Cg factor is the same. I suppose with my limited knowledge I was just considering it logically by trying to create more 'air' by removing the sheaving so the resulting singles weren't touching, but as this can't be guarenteed the Cg must be considered.

Thanks again everyone who took the time to add comments.

...Achillies