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Topic Title: Conductor derating factors for internal panel wiring
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Created On: 17 September 2013 03:39 PM
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 17 September 2013 03:39 PM
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MatthewJScott

Posts: 4
Joined: 17 April 2013

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

I have a panel with 6 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
 17 September 2013 07:03 PM
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Legh

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Joined: 17 December 2004

I'm not sure about the regulations regarding panel wiring inside appliances / machines but as the electrical current is likely to be the same whether inside or outside of the machine then I would consider the thermal conditions to be similar as that in conventional trunking.

However, much of the internal wiring is boot-laced tightly together for neatness so this might be a factor to consider

Legh

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 18 September 2013 02:31 PM
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MatthewJScott

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Cheers for the thoughts Legh... it does make sense to consider the grouping factors for internal panel wiring and for the factors to be similar to the factors for conventional trunking but i would like somebody to point me in the right direction with respect to the standard.

Thanks again, Matt.
 25 October 2013 01:48 PM
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ysohail78

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Joined: 01 June 2012

U should consider the derating factor in same manner as being considered for multicore cables. the trunking inside ur panel shall be filled not more than 70 to 75%. Though the loss in cables is less as most are control cables n control circuits

Youns
 03 November 2013 05:25 PM
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davidburke

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Joined: 28 April 2010

Matthew,

I work at a panel manufactures and have the same problem as there doesn't seem to be a clear spec or standard for de-rating on wires in types of plastic trunking, however, as a rule of thumb you should never exceed 60% fill capacity of the trunking (this puts you in line with most standards including some nuclear standards) and your losses won't be as high as those if you loom or put wires through conduit.
I am assuming your panels are to BS EN 60439-1:1999 Low Voltage Switchgear and Controlgear Assemblies or the updated version BS EN 61439:2009 Low Voltage Switchgear and Controlgear Assemblies? Making sure your cables are rated for short-circuit withstand as well as current carrying capacity? I would generally look at how full your trunking is going to be? how tightly packed your wires are going to be? what ambient temperature your panel is going to be at? what type of cable you are using (tri-rated, LSZH, type 4c)? and just apply a method of logic to it. I'm guessing this is a new system and therefor you can put larger trunking in if necessary so just de-rate your wires by around 20-30%, this should give you enough breathing space should it be modified in the future without giving your a higher costs due to larger cables.

Hope this helps.

David
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