4 core vs 5 core cables

Question

Hi, 
 
 I do a lot of cable calculations for Electric vehicle chargers and it is often that our client wants to run the cabling as 5 core, with the 5th core as the earth. 
 
 My question is, what is the correct way to do this. I have always used XLPE/SWA 4 core and then selected the CPC to be 'Live Core', which then takes (i believe) the 5th core to be the same size as the cable is fixed at. 
 
 However, a senior electrical engineer at the company selects 'armour & auxillary' and then fixes the CPC size to be the same as the fixed cable size. 
 
 Please can someone let me know which method is correct and how much of a difference the two methods will have on the CPC size, if any. 
 
 Thanks, Luke

Sayan Acharyya · Answer

Hi Luke, 
 I would personally suggest that it may not be a case of which is correct / incorrect, but which closer approximates the design you wish to achieve - in general I would always advise choosing the most conservative option to ensure a factor of safety. Not sure if suits your needs, but another approach may be to add your own specific cable for this situation via 18th Edition > Cable Data > Add new cable file (eg as below), as then you will have full control over its data? 
 Regards, Sayan