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Topic Title: BS EN 60204-1 requirements for derating internal panel wiring
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Created On: 19 September 2013 09:44 AM
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 19 September 2013 09:44 AM
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MatthewJScott

Posts: 4
Joined: 17 April 2013

Re posted in this forum as i have had little response in the control and automation forum.

Do derating factors have to be applied for grouping of conductors in the plastic trunking inside of panels?

I have a panel with 4 loaded circuits running in single core cables in the same piece of trunking from contactors down to the terminal rail at the bottom of the panel. I am trying to work out whether i need to apply grouping derating factors to the Iz of these cables. The temperature is not an issue.

BSEN60204-1:2006 Table D.2 gives derating factors for grouping of circuits but the only reference to single core power cables is installation method B1 (single core cables in conduit and cable trunking systems). Does this method cover internal panel plastic trunking or just trunking between panel enclosures?

Any help or clarification will be greatly appreciated.

Cheers

Matt

Edited: 27 September 2013 at 11:25 AM by MatthewJScott
 19 September 2013 10:15 AM
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AJJewsbury

Posts: 10963
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Try thinking about it from the point of view of the laws of physics rather than the wording of standards, at least in the first instance.

The temperature is not an issue.

Grouping factors are all about allowing a conductor to dissipate heat created by I²R losses - which is naturally easier if it's surrounded materials or air at ambient temperature rather then other cables at much the same temperature as itself. From that point of view, it's all about temperature.

Once you've got the basic principles figured out, the wording of the standards should hopefully make more sense.

- Andy.
 20 September 2013 11:13 PM
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gkenyon

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Yes, I believe derating is required, but a derating factor for the ambient temperature inside the panel should also be considered where appropriate.

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Eur Ing Graham Kenyon CEng MIET
 21 September 2013 10:14 PM
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whjohnson

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I just use Tri-rated singles for panel wiring - it saves having to faff about with de-rating factors.

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 22 September 2013 09:51 AM
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MickeyB

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Agreed, tri rated is the way to go....... these cables worked 25 years ago..... see no reason why they wouldn't work now. 105 degree's is pretty hot.....
 23 September 2013 10:24 AM
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AJJewsbury

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I just use Tri-rated singles for panel wiring - it saves having to faff about with de-rating factors.

Why does using tri-rated (cable that complies with US, Canadian and British/European standards) make a difference? Isn't terminal temperature still the limiting factor?

- Andy.
 27 September 2013 11:21 AM
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MatthewJScott

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Thank you for the replies,

whjohnston, MickeyB, I am already using tri-rated singles but i believe the derating factors for temperature and grouping still apply.

AJJewsbury, when I said 'temperature is not an issue' I should have said 'ambient temperature is not an issue' . The maximum ambient temp in the panel is around 35C. I would still be wrong as looking at table D.1 in the standard, 35C will give a correction factor of 1.08 which will offset the effects of grouping somewhat.

I agree with your analysis and I too believe that the derating factors should be applied but from the standard it is not clear which, if any derating factors should be applied to the internal planel wiring. My gut feeling is that Table D.2 Installation method B1 should be used which leads me to the following for one of my circuits which comes from a contactor down to the power terminal rail:

Design current is 28A (3Phase)
MCB is set to 29A
Ambient 35C Max (factor = 1.08 from table D.1)
Grouping will be 4 (factor = 0.65 from table D.2)

Total correction factor = 1.08 x 0.65 = 0.702

4mm Tri Rated : Iz = 41A, corrected = 28.78A (Too small)
6mm Tri Rated : Iz=53A, corrected = 37.21A (OK)

In conclusion

After applying correction factors the size required goes from 4mm to 6mm.

Do you agree that this is the correct application of the standard?
 27 September 2013 11:41 AM
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OMS

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Joined: 23 March 2004

Generally, Matt - yes it is

Regards

OMS

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