space factor

[20al]

would 12x4mm single cables in a 25mm conduit exceed allowed sspace factor ?

 

[ringer]

Before you start thinking about grouping factors etc have a think about whether you can physically get 12x4mm singles in there. Are there going to be any bends to get these cables round?

 

[20al]

well,believe it or not the answ is yes, you can physically do it, cos i have done it,bends and all,plenty of the yllow stuff and pull like ****. i wasnt happy doing it but the ****e firm am working for insist on it. Theyre saving on conduit runs !!!

 

[Sparky Ninja]

Are there bends or is it a straight run?

Straight run
(not exceeding 3m, or with an accessible box at each 3m interval)=

4mm Cable factor of 58, total cable factor of 696 (12x58).
25mm Conduit factor is 800.

So, by the numbers this would be acceptable.


Run exceeding 3m and/or with bend=

4mm Cable factor of 43, total cable factor of 516 (12x43).

Now if it is a straight run, 3.5m has a factor of 521, whilst 4m has a factor of 514. So 3.5m is the limit.
If the run incorporates 1 bend, 1.5m has a factor of 528 and 2m has a factor of 514. So 1.5m is the limit.
If the run incorporates 2 bends, 1m has a factor of 514. This means 2 bends shouldn't be considered.
3 bends follows suite with a 1m factor of 463, and 4 bends has a 1m factor of 388.

 

[20al]

Yes mate,there are bends in it !

 

[Sparky Ninja]

Yes mate,there are bends in it !

Well hopefully it's a very short run then.

 

[20al]

Thanks widdler, but am still a bit confused.The installation is a hospital ward with one conduit 25mm carrying 2 ring mains. T boxes used to supply individual sockets,but there are runs of at least 3m with a 90 bend between boxes with 12x4mm cables. hope am explaining this ok to you.

 

[20al]

widdler,just ran by your calcs again and it looks like we are well over the limit, are your calcs regulation or reccomendation ? thanks for your time.

 

[Sparky Ninja]

widdler,just ran by your calcs again and it looks like we are well over the limit, are your calcs regulation or reccomendation ? thanks for your time.

Quoted from the on site guide mate.

 

[tonys]

well,believe it or not the answ is yes, you can physically do it, cos i have done it,bends and all,plenty of the yllow stuff and pull like ****. i wasnt happy doing it but the ****e firm am working for insist on it. Theyre saving on conduit runs !!!

If you don't like it, someone else will take your job.

Wonder how the preachers of BS7671 would survive in the real world of economics?

 

[rocker]

I wonder if I'd still have a pension if the real world of economics stuck to the rules.

 

[jaresquire]

Did install of Cat5E for a company, the runs were from a roof space with containment provided by electrical contractor;
9 in 20mm conduit
12 in 25 mm conduit
All runs had at least 3 90 degree bends.
Ended up soaking in Yellow77 and wrapping around a scaffold pole to get leverage.
Cables must've stretched but passed certification tests just fine!

 

[tonys]

Did install of Cat5E for a company, the runs were from a roof space with containment provided by electrical contractor;
9 in 20mm conduit
12 in 25 mm conduit
All runs had at least 3 90 degree bends.
Ended up soaking in Yellow77 and wrapping around a scaffold pole to get leverage.
Cables must've stretched but passed certification tests just fine!

lol I shouldn't laugh really

 

[Engineer54]

I find the UKs conduit rating factors totally confusing, and often revert back to the old 14th ed of maximum numbers of a given sized conductor for each size of conduit and the 40% free space, ....Still works for me!!!

 

[tonys]

Ain't trunking still got the 40% factor?