400V cable derating - strange configuration

[123MB]

Hi All

I am looking for any standard that has an ampacity derating rule that can be applied to the following case:

A circuit is comprised of 3-off 3 core cables connected in parallel. The multicore cables making up the parallel group are touching, in trefoil there are 3 of these groups touching on cable ladder,​

So practically it is 3 groups of 3 multicore cables, each group laid in trefoil

I am willing to pay for any standard (BS, NEC, IEC) if it has a case I can apply to this cable arrangement.

I am also willing to consider the cable arrangement equivalent to 12 multicore cables, with 6 layed directly on top of another 6, in cable ladder - if that helps

I am a little bit desperate Thanks for your help

Cheers Michael

 

[magoo2]

We use the CYME ampacity program to calculate the ampacities of various cable arrangements. You might check with them. They are in Canada.

We normally use single phase cables in the U.S., so I don't have any ready answers that would help further with three phase cable arrangements with trefoil.

Good luck.

 

[7anoter4]

In my opinion you could follow -one of- these publications:
ICEA-NEMA Standards Publication No. P-54-440, "Ampacities Cables in Open-Top Cable Trays"
Or the new one:
NEMA WC 51 AMPACITIES OF CABLES INSTALLED IN CABLE TRAYS ** SAME AS ICEA P-54-440 **

 

[mbk2k3]

have a look at this:

http://www.openelectrical.org/wiki/index.php?title=Grouping_Derating_Factors

 

[7anoter4]

The link is interesting but –in my opinion-between cable layers has to be a distance [see note one in IEC 60364-5-52 table]:
(1) Vertical spacing between layers is at least 300mm and there is at least 20mm horizontal clearance between the layer and wall
That means the cables are touching horizontally but are not vertically.