IEC 60364-5-52 Multilayer cable routing reduction factor sizing

[qqitek]

Hello Folks!

I have question regarding IEC 60364-5-52 regarding approved methodes of cable routing via ladders/trays and derating factors.
Q1) Table B.52.17 item 1.
Can we use the worst reduction factor (0,38) for multilayer cable routing? It is very often that cables are laid on several layers laying each on other.
I would like to know how to derate cables in such situation?

Q2) If above is not accepted for multilayer laying of cables, look on IEC 60364-5-52 Table B.52.20 NOTE 2:
"NOTE 2 Factors apply to single layer groups of cables as shown above and do not apply when cables are installed in
more than one layer touching each other. Values for such installations may be significantly lower and has to be
determined by an appropriate method."

What is the "appropriate method" of calculating reduction factor in this case?

Any ideas?

thanks in advance,
qqitek

 

[7anoter4]

Power cable in a solid bottom cable tray filled randomly could be extracted from:
ICEA STANDARD PUBLICATION NO.ICEA P-54-440/NEMA WC 51-2003
or calculated based on
Ampacities for Cables in Randomly Filled Trays
by J. Stolpe
Nevertheless the conductor cross section area is AWG/MCM one may take the next bigger cross section and the
result will be fair.

http://www.google.co.il/url?sa=t&rc...440&source=web&cd=2&ved=0CFIQFjAB&url=http://

http://www.nema.org/Standards/Compl...x4HwDg&usg=AFQjCNH6aO4hap4woDx3riAwqEXJkbkakg

 

[qqitek]

Thank you 7another4

For the moment I do not have access to NEMA WC51.
But can you confirm that this standard determines the multilayer cable filling (high filling of tray) or randomly circuit?
This makes difference.
Random issue is important, but now I have trouble with high filled trays, and calculation of this situation.

Regards
qqitek

 

[7anoter4]

In the "Scope" of this Standard it is mentioned:
"This Standards Publication covers ampacity for -15,000 volt solid dielectric insulated single-conductor,triplexed,and three-conductor cables
having a calculated depth up to three inches when installed in open-top cable trays."
In the ch. "CALCULATED DEPTH OF CABLES IN CABLE TRAYS" it is written:
"The depth of cables in trays should be calculated as follows:
Calculated Depth,inches=(n1*d1^2+n2*d2^2+....+nn*dn^2)/w
where:
d1,d2...dn = diameter of cables,inches
n1,n2.....nn=number of cables of diameters d1,d2...dn,respectively.
w=width of tray,inches."
That means the cable tray is filled with cables of different diameters from one cable up to n cables per same diameter.
The order is not important.
The Ampacity Tables are produced filling the cable tray with the same type of cable for different calculated depth.
Following this way I calculated the reduction factor as per IEC 60364-5-52
I did it for 4 cables 3*50+25,3*70+35,3*120+70,3*240+120.In IEC Standard is only for perforated tray indicated but in IEE is for solid bottom.
cable one cable in free air one layer -9 cables touching two layers three layers
cross section per IEC calculated [A] calc. IEC [A] [A]
3*50+25 192 190 130 0.68 0.73 88.2 0.46 67 0.35
3*70+35 246 237.38 165.38 0.67 0.73 109.1 0.44 82.35 0.33
3*120+70 346 336.74 238.89 0.69 0.73 152 0.44 113.4 0.33
3*240+120 538 524.88 361.72 0.67 0.73 231.2 0.43 170 0.32

 

[7anoter4]

It seems the Cables in Cable Tray Ampacity Table was not presented well. I sent a jpg file for better reading.