cables suspended between joists?

[antsbradley]

Hi,

As I understand the regulations, horizontal cables should be clipped at least every 250mm, so what about when they are run thru a series of joists at 400mm centres?

I dont recall ever seeing any additional support for cables in floors, so is it within the regs that the cables are only supported every 400mm by the joists they run thru?

Thanks Anthony

 

[Chri5]

No need, assumption being that the cable is laid on floor between joists, so is supported.

 

[Steve]

No need, assumption being that the cable is laid on floor between joists, so is supported.

Erm, this should never happen should it? If the cable is passed through the middle of the joist (as it should be), it would never (hardly ever) touch the bottom of the void (except where it turns to run with the joist).

It would happen even less often if the wood butchers had been out notching joists.

 

[antsbradley]

Cable is passing thru middle of joists and not sitting on floor / ceiling etc, just in mid air between joists, is it still ok?

 

[rebuke]

It would depend how wide the gap is - if it was only a short gap then it would be held above the ground, but then the joists would be close enough together to provide adequate support. If the joist centres are too far apart from that, then the cable will drop down to the floor and be supported by that, the height difference between the hole in the joist and the floor is pretty small...

 

[conny]

the height difference between the hole in the joist and the floor is pretty small...

Must be at least 50mm. (2")

 

[Chri5]

Well then why not consider it as an aerial (catenary) cable between each joist, then you have 3m per table 4B OSG.

The alternative is to avoid having the cable as tight as piano string between the joist holes, so it does sit on the void floor and hence is supported.

 

[toasty]

I've often wondered the same with street lights.

They must be 8 metres high and I think I'm right in saying that the cable just drops down inside the pole (sometimes you can hear it hitting the inside when they move slightly in the wind)

There is a similar regulation for clipping vertical cables, which doesn't seem to be adhered to in this case.

I don't know how long a length you would need, and obviously it would be a massive amount, but there would presumably come a time when a length of cable hung vertically would snap under its own weight? More likely though is that a fairly long piece would stretch under its own weight.

 

[chivers67]

//www.diynot.com/wiki/electrics:installation_techniques:route Have look here for some useful info

 

[ban-all-sheds]

 

[Pensdown]

Hi,

As I understand the regulations, horizontal cables should be clipped at least every 250mm,

I think you're getting confused between Regulations and Guides.

Regulations 522.8.4 & 522.8.5 are the ones your looking for and neither quote support distances.

522.8.4 - Where the conductors or cables are not supported continuously due to the method of installation, they shall be supported by suitable means at appropriate intervals in such a manner that the conductors or cables do not suffer damage by their own weight.

So if you think that the cable you intend to use (probably 1.5-2.5 T&E) will be damaged by it's own weight when spanning 400mm then by all means support it.

Personally, I think you would be wasting your time.

 

[antsbradley]

[quote="Pens";p="1143796I think you're getting confused between Regulations and Guides.

Regulations 522.8.4 & 522.8.5 are the ones your looking for and neither quote support distances.

522.8.4 - Where the conductors or cables are not supported continuously due to the method of installation, they shall be supported by suitable means at appropriate intervals in such a manner that the conductors or cables do not suffer damage by their own weight. [/quote]

Great, thanks for claryfing the difference!

Ants

 

[Lectrician]

I've often wondered the same with street lights.

They must be 8 metres high and I think I'm right in saying that the cable just drops down inside the pole (sometimes you can hear it hitting the inside when they move slightly in the wind)

There is a similar regulation for clipping vertical cables, which doesn't seem to be adhered to in this case.

I don't know how long a length you would need, and obviously it would be a massive amount, but there would presumably come a time when a length of cable hung vertically would snap under its own weight? More likely though is that a fairly long piece would stretch under its own weight.

And what surprises me is that they use T+E and not flex. T+E is meant to be clipped and kept still so to speak.

They do use 2.5mm usually, but it still seems a little odd.

When you install galv trunk in vertical runs, you are meant to use "pin trunking" which has pins that you 'zigzg' the cable through. In all my time I have never seen this, and have installed countless installs with trunk, and worked on even more.....including many from the 60's/70/s and 80's..........and the modern era too!

 

[Stoday]

That's a joist hanger BAS. You don't use it to hang cables with.

 

[ban-all-sheds]

No - but you could use them to support trunking running between the joists..

Mind you - these would be better...