Cable calculation - Derating factors

[Basil brush]

This is my first time here so please go easy ?

I am currently designing some circuits for large convenience store and I have a question about the thermal insulation derating factor. A radial circuit will feed two display fridges, total load 10A. The circuit will run from the DB through the roof space on a perferated tray to the back of the shop. It will then be installed inside a 50mm aluminium stud wall with thermal insulation.

My question is, do I de-rate the cable by half as it's running from ceiling to floor level? (in excess of 500mm)

Or

Calculate without Ci and choose ref method 102?

Thanking you in anticipation

 

[Wilko]

Hi - which factor to use depends on exactly how the cable passes down the wall. From what I’ve understood, it seems it’s either IM102 or (more likely) 103, from Table 4A2. This leads us to Table 4D5 and the various ratings. As you say, 103 is 50% of Clipped Direct and that’s what I’d probably use.

 

[telectrix]

2.5mm radial will allow you 13A as a worst case of derating (ref. 103), so that's what i'd fit. probably OCPD 16A.