Cable sizing grouping factor by number of circuits

Dear Sir,

In direct burial installation of cable,

I found Grouping factor for number of circuit is limited by 6 circuit in your calculation tool.

More than 6 circuit does not impact any more on the grouping factor.

Could you give me detail reasons why maximum 6 circuits are only applicable for the derating? I remember IEC, ERA has derating factor upto 20 circuits.

Thanks in advance.


asked 11/30/2017
고성윤3
고성윤

4 Answers


answered 12/12/2017 Todd Peters 3
Todd Peters
edited 12/12/2017
Todd Peters3
Todd Peters

The derating factor is in line with table 4C2.  This table only goes up to six circuits (with a maximum derating factor of 0.55 in your case).  In the tool for all conditions, we allow up to 20 circuits for all installation conditions.  For any number of circuits above 6, will use the maximum derating factor, which is for 6 circuits.  Hope this makes sense.

Other derating tables do have more than six (with the maximum being 20).

Please also note that we are not supporting this particular tool going forward.  It has been superseded by our cable sizing application,  myCableEngineering.com.  I would suggest you give this a go, as you have more options and it is far easier to try out different scenarios. 

 

 

answered 12/7/2017 Steven McFadyen 242
Steven McFadyen

Thanks for your quick reply and please find two(2) captured screens below.

One is calculated with circuits 6 no and the other with circuits 20 no, and expected different groupinf factors.

However, calculation result was same with grouping fator with 0.55.

Please let me understand why grouping factor does not change although the circuit numbers are increased.

 

answered 12/7/2017 고성윤 3
고성윤

I am seeing up to 20 circuits on the cable tool.   Could you post a screenshot for me to look at (there is an insert media button, in the middle of the editor top bar)?  I can then look at the issue.

In addition to the calculation tool on myElectrical.com, which is BS 7671 if you are interested in ERA you could also look at myCableEngineering.com.  Here you can do both BS 7671 and ERA 69-30. Additionally, you have better cable management,  installation options, reporting and your cables are saved. 

 

 

answered 11/30/2017 Steven McFadyen 242
Steven McFadyen
  • Thanks for quick reply and added question with screeen capthres. - 고성윤 12/7/2017

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