Sizing of Conductores - IEC

[pdias]

Hi! I'm selecting the conductors according the IEC 60364-5-52 in a Substation. We're using concrete cable trays like the following:

They are sheathed multi-core cables.

Regarding with the reference number and the method of installation to be used for the calculations i thing of use the following:

Do you agree that this the is correct one?

Thank you in advanced.

 

[che12345]

pdias (Electrical)(OP)30 Aug 24 17:49
'... We're using concrete cable trays like the following ..see pic*. Regarding with the reference number and the method of installation to be used for the calculations i thing of use the following Item 56, Ref B1 ..'
I have the following opinion for your consideration.
1. Item 56, Ref B1 "...in an open or ventilated cable channel run...".
2. Attention: Based on the picture*, the top slab is NOT ventilated. Therefore, the current rating is expected to be lower. A factor say < 1.0 .
Che Kuan Yau (Singapore)

 

[7anoter4]

Few remarks:
1) the trough[or concrete tray] is closed with a concrete plate[ a lid] only.
2) the plate is exposed [to free air but to sunshine also?]
3) if it is embedded, how deep?
If we decide to neglect the sun radiation then Reference method D, item 70 of table 52-3, (multi-core cable in ducts in the ground) it seems to me will be closer.
See attached here a study of a cable installation in similar trough.

 

[che12345]

'..Reference method D, item 70 of table 52-3, (multi-core cable in ducts in the ground) it seems to me will be closer..'.
1. I think it is closer to Item 57 Ref C.
2. Note: Item 70 Ref D is applicable for "..cables are in conduit or in cable ducting in the ground..."
Che Kuan Yau (Singapore)

 

[pdias]

Hi che12345
Hi anoter4

First let me thank you for your time and for your opinion in this subject.

Since the concrete tray are not ventilated I agree with both of you, I must choose another method.

The concrete tray runs with the lid at the ground level (0,00) and the bottom of the concrete tray runs at a deep of -0.80 cm.

7anoter4 thank you for the study I will check it out for sure.

There are more methods, and perhaps the 51 it's the most suitable for this situation. What do you guys think?

 

[7anoter4]

As it is declared somewhere in the text, the calculation in IEC 603564-5-52 standard follows the IEC 60287 way. So, in my opinion, the 51 item is according to the volume 60287-2-1 chapter 2.2.6.2 Unfilled troughs of any type, with the top flush with the soil surface and exposed to the free air, then no lid is present.

 

[St_Isakovic]

In my experiance with ducts like this, they will not be completely sealed. In time they will fill with dirt, also water will be washing mud on cables. I don't know the circumstances, maybe conditions in your case will be better, but if I had to sign this project, I would go with item number 71, instalation method D1.

Now current capacity is different for these two methods, so using method D1 would increase the cost. This could be substantial, or not if cables are Al and distances are short.

 

[pdias]

Hi 7anoter4,

I'm still confused about the corrected method to be use.

The following IEC table defines that the cable channels methods are:

I know that none of the methods represents an "unfilled concrete cable channel with the top flush with the soil surface that is buried at 0,7 metres (not 0,8 metres as I said before) in ground".

Pehaps the most suitable method is the "56 - Sheathed single-core or multi-core cable in an open or ventilated cable channel run horizontally or vertically", i know that is not a ventilated channel, but it is very close from the surface.

It's not also a fully buried in ground cable trough like in method 70 "Multi-core cable in conduit or in cable ducting in the ground". trough like in method "70 - Multi-core cable in conduit or in cable ducting in the ground".

It's not also embedded in the strucuture like method "51 - Multi-core cable in flush cable trunking in the floor"

I'm really confused at this moment.

From all the methods what it is the closest to my situation?

Thank you in advanced.

 

[7anoter4]

In my opinion, the IEC 60364-5-52 standard it is only for information. The actual standard-
which is compulsory in each country is more specific. For instance, BS 7671-I have only 17th edition [2008]-Table 4A2 for installation methods from 118 up to 120, for cable enclosed in trench or in an infloor concrete trough with dimensions of 450 wide and 600 mm deep or 600 mm wide and 760 mm deep including 100 mm cover it is closer to your case. The reference method to use to determine current carrying capacity recommended it is E or F using rated factors from Table 4C6.

 

[7anoter4]

BS7671 Installation Method 120

 

[7anoter4]

BS7671 Table 4C6

 

[pdias]

Thank you 7anoter4 for your help.
Thank you St_Isakovic for your contribution.