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Topic Title: IEE Wiring Regulation - Grouping factor
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Created On: 12 May 2013 06:28 AM
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 12 May 2013 06:28 AM
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tonychu1

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Based on the IEE 17th Appendix 4 Table 4C1 Note1

Should Grouping Factor (no. of cct=2) be applied to a single phase circuit design with two identical single-core live & neutral conductors connected in parallel?

Edited: 12 May 2013 at 06:37 AM by tonychu1
 12 May 2013 08:21 AM
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aligarjon

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grouping is based on the number of circuits not conductors.

Gary

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Specialised Subject. The Bleedin Obvious. John Cleese
 12 May 2013 08:36 AM
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Christof

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Originally posted by: tonychu1

Based on the IEE 17th Appendix 4 Table 4C1 Note1



Should Grouping Factor (no. of cct=2) be applied to a single phase circuit design with two identical single-core live & neutral conductors connected in parallel?


Grouping factor's need to be applied for Parallel Cables.

Chris
 12 May 2013 05:43 PM
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ebee

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Originally posted by: aligarjon

grouping is based on the number of circuits not conductors.



Gary


Surely not?

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Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 13 May 2013 01:39 PM
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AJJewsbury

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Surely not?

I would have thought it was - it's all down to heat - 2 sets of cables carrying 30A each will produce the same amount of heat whether they're connected to two 30A fuses or one 60A one.

As I see it the phrase "one circuit" of singles in appendix 4 context is just a shorthand for whatever the arrangement of conductors you assumed when looking up the cable's tabulated CCC - e.g. two live conductors for a single phase circuit or three lines, or three lines plus one neutral, for a three-phase circuit.

- Andy.
 13 May 2013 01:49 PM
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OMS

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Perhaps a read through notes 3, 4 and 5 will clarify.

Worth also a look at 2.3 et seq - particularly the note to 2.3.1 and 2.3.3

regards

OMS

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Failure is always an option
 13 May 2013 02:17 PM
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Parsley

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Note 5 of Table 4C1

"If a group consists of n single-core cables it may either be considered as n/2 circuits of two loaded conductors or n/3 circuits of three loaded conductors."

Regards
 13 May 2013 04:27 PM
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broadgage

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Originally posted by: aligarjon

grouping is based on the number of circuits not conductors.

Gary


Can not agree.
If cables are paralled then they will produce the same heat as they would on individual circuits and therefore both common sense and the intent of the regs would suggest that the same degree of de rating should be applied.

I cant see that 4no cables in two paralel pairs would have a greater current carying capacity than the same 4 cables used for 2 seperated circuits.
 13 May 2013 10:56 PM
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aligarjon

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rightly or wrongly i read the OP as a single circuit where the conductors had been double up to get a satisfactory csa so spreading the load equally down both sets of cables.
From what you are saying, and i can understand where you are coming from, that would mean you would have to apply a grouping factor to a single 3 phase circuit wired in singles ?

Gary

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Specialised Subject. The Bleedin Obvious. John Cleese
 13 May 2013 11:05 PM
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OMS

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From what you are saying, and i can understand where you are coming from, that would mean you would have to apply a grouping factor to a single 3 phase circuit wired in singles ?


How so ? - you'd select from the relevant column of 4D1A fo a 3 phase circuit - which is already derated compared to a single phase circuit.

Ie you have 3/3 conductors using note 5 to table 4C1 = 1

so no grouping applied and use the 3 phase CCC

If you were installing 2 conductors per phase on that 3 phase circuit, you use the three phase CCC x 2 and derate by 0.8 as it's now grouped.

ie 6/3 = 2 circuits grouped applied to the three phase CCC

Regards

OMS

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 13 May 2013 11:09 PM
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aligarjon

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Thanks OMS . as you can probably tell i only tend to do domestic works and do very little calculation work. thanks for the lesson.

Gary

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Specialised Subject. The Bleedin Obvious. John Cleese
 13 May 2013 11:13 PM
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OMS

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My pleasure - now go and decide if the two legs of a ring dropping down the wall are "grouped"

Regards

OMS

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 13 May 2013 11:37 PM
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aligarjon

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i think thats where i got confused because i know they aren't.



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Specialised Subject. The Bleedin Obvious. John Cleese
 14 May 2013 12:01 AM
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OMS

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Well, that's debatable actually, but yes, we don't treat it as grouped because of current sharing around a ring.

For what it's worth, you probably wouldn't consider grouping of ring circuits until you had at least 3 RFC's running together

Regards

OMS

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Failure is always an option
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