IEC60364-5-52 Cable Ladder Reduction Factor Spacing

[jesswilson]

Hi all,

I was wondering if anyone was familiar with IEC 60364-5-52, Table B.52-20, method of installation E32 (using Cable ladder/tray) and de-rating cable as a result of stacking multiple levels of tray vertically.

The standard clearly states that the tray shall be greater than or equal to 300mm from ladder rung to ladder rung, and the table then specifies the de-rate factor for the cables as more and more trays/ladders are stacked vertically. The table illustrates the de-rate factor to apply to a cable based on a 1, 2, 3 and 6 tray stack, again with the 300mm minimum spacing.

My question is, does anyone know of any IEC or EN standard that specifies the minimum vertical distance between trays before the de-rate is a multiple of 1.00 again, for example, like it's a single cable tray/ladder in free air, minimum 20mm from a wall? I understand the standards intention is because of heat from the cables below heating the cables in the trays above.

My situation is I have a very narrow, long and tall plant that I'm working with. Some runs follow the length of the building and I would like to minimize my cable de-rating as much as possible if I can use the height to space the cable tray significantly enough. However, the IEC standards I've seen are silent on this and the >=300mm spacing is suggesting that if you had 3 trays stacked but the third one was 3 meters higher, then you would have to de-rate cables as if it were 300mm above. Any thoughts or experiences?

Thanks in advance.

 

[juleselec]

The IEC standards aren't so ridiculous as to impose such stringent blanket requirements on vertical spacings

Annex B of IEC 60364-5-52 is really there for guidance in the most common situations, and I'd say it's useful 99% of the time. But when you get stuck, you have to go back to the IEC 60287 series. In your case, have a look at IEC 60287-2-2.

The long and the short of it is that the ratio of the vertical spacing (e) to the external diameter of the largest cable (De) needs to be greater than 4 (i.e. e/De > 4) for there to be no derating (see Table 1 of IEC 60287-2-2). There is also a requirement about heat dissipation coefficients that you'll need to check out, but my guess is that a 3m high spacing would be ample.

 

[7anoter4]

According to DIN VDE 0298/ part 2 "Application of cables and flexible wires in power installations. Recommended values for current-carrying capacity of cables for fixed installations with rated voltages VO/V up to 18/30 kV" the minimum vertical distance between two cable trays is only 200 mm.
Attached here is a copy from ABB Switchgear Manual translated from DIN VDE 0298.