The tables in the regs are only a guide to the most common situations,  you will often find yourself staring at something and asking ' is this more like clipped direct or on a tray ?' or some similar. Even then it is all a bit approximate - clearly convection cooling varies with up or down versus sideways cable directions  but only a single figure is given. So think about the degree of cooling in your particular scenario, and decide which case it matches, and if in doubt, err on the side of using a slightly larger cable or running things at  less current than abs max. Also beware of the grouping factor if it all converges horribly in a riser/ duct  or similar If you have a specific situation, feel free to come back, maybe post a picture of the problem point and there are plenty of folk here who can advise.

Mike.

The tables in the regs are only a guide to the most common situations,  you will often find yourself staring at something and asking ' is this more like clipped direct or on a tray ?' or some similar. Even then it is all a bit approximate - clearly convection cooling varies with up or down versus sideways cable directions  but only a single figure is given. So think about the degree of cooling in your particular scenario, and decide which case it matches, and if in doubt, err on the side of using a slightly larger cable or running things at  less current than abs max. Also beware of the grouping factor if it all converges horribly in a riser/ duct  or similar If you have a specific situation, feel free to come back, maybe post a picture of the problem point and there are plenty of folk here who can advise.

Mike.

Hi, i'm referring to table 4D5 in the BS 7671. Apart from reference method C, all the other columns refer to insulated walls and ceilings. I don't have insulated walls and ceilings for my project. What alternative tables can i use?

4D2A

You can safely assume that flat T/E cables dissipate heat in a similar or slightly better way compared to an equivalent cross-section round one for example so you can estimate to within a few percent by reading across from other tables. To be honest I'll be surprised if the design is limited by the cable rating in the walls - usually it is the grouped sections that determine the minimum cable size.

Mike.