I agree with Andy - unlikely BS7671 applies inside a control panel.

If you are concerned about grouping, then can you provide more diverse routing inside the panel to reduce these factors? 

I have had a similar issue but the other way round - the grouping/sizing on the field cables was the cause of my problems. 

Jason.

I agree with Andy - unlikely BS7671 applies inside a control panel.

If you are concerned about grouping, then can you provide more diverse routing inside the panel to reduce these factors? 

I have had a similar issue but the other way round - the grouping/sizing on the field cables was the cause of my problems. 

Jason.

I agree that BS7671 isn't the correct approach, rather BS EN 61439-1/2 for control assemblies is, and this standard often makes reference to BS EN 60204-1 (safety of electrical machines) ... it is a control panel for a machine i'm working on.

However, BS EN 60204-1 doesn't help with my question on slotted trunking either. The cable calculations are very similar (if not identical) to BS7671 of which i have Trimble software to back up my long hand attempts! And I think ultimately all these electrical standards come from the same source (physics) and are similar in many aspects, especially cable calculations.

The slotted trunking, the purpose of which is more for cable tidiness than mechanical protection, has gaps both sides greater than 30% of its surface area  (the requirement for perforated tray)  albeit it comes with a lid. I guess I was hoping someone has had come across this issue before and might argue it is reasonable to reference slotted trunking the same as perforated tray because the air flow can easily pass through it.

I have increased my conductor size to 50mm and run the cables in separate lengths of trunking to avoid grouping of more than 2 circuits. It just would have been great if I could have used 35mm cable, i've been lucky this time with the few circuits i am dealing with but I  might have had a real problem.