Yes  - if you take the BS 7671 figures and correct them to match the BICC Data, they will match up


BICC is simply quicker and easier to use as it's already corrected to realistic ground conditions whereas usually you need to correct the BS 7671 figures to the realistic ground conditions.


Compliance with a table, isn't necessarily compliance with BS 7671, even if the table used is BS 7671 - if that makes sense


Regards


OMS

Thank you for your response OMS. By "correction", do you mean applying de-rating factors for different conditions or do you mean something else not included in BS7671? 


If the values match up exactly then its not an issue but I have had situations where BS7671 gives a higher required cable size compared to BICC, according to Amtech as I do not have a copy of BICC data. For example, for the following conditions, I was getting minimum 95mm^2 (BS7671 installation method 70) vs 70mm^2 (BICC in Underground single way ducts) for a 4 core cable with SWA and XLPE insulation (ie 90C). In this case, would you say there is any reasonable justification to go with the lower BICC cable size if calculations based on the standard suggest a larger cable size?


1 - Depth of lay - 0.8m

2 - Spacing,

3 - In ducts or buried direct - ducts

4 - Ground Temperature - 15degC

5 - Soil Thermal Resistivity - 1.2K.m/W

6 - Air temperature - 30degC

Yes, de rating factors if you like


First have a read of Appendix 4, section 7.1 where it relates to installation method D


Then take the data for "BICC" installations in Amtech and apply that to the BS 7671 data for all the parameters you list (noting Table 4B4 doesn't have a correction for 0.8m depth of lay)


Check if BS 7671 is applying the Factor Cc of 0.9 for all buried cables (direct or in ducts) as Equation 1 in 5.1.1 in Appendix 4


If you still have a difference, put it down to manufacturers testing being mare accurate than BS 7671 values which may have 5% variations used (and up to 10% on buried cables) which tend to be on the conservative size


As a sanity check, see if your calculations show more than 10% variation, which may well be the Cc factor above which BICC data doesn't use (although it may be applied equally by Amtech to either case)


I've run calculations using BICC data and BS 7671 data with very good agreement of out turn cable size - so it may be an Amtech glitch


Regards


OMS

BS6761 was never used as the last word for big installations that have a lot of buried cable, e.g. power stations, (apart from the "domestic" side of things). The CEGB had their own methods and ratings often based on different assumptions but equally well researched. As the BS is based on the manufacturers data - with one set of assumptions as to installation method -, using the manufacturers figures should give you more accurate figures if the BS assumptions are not relevant in your case.