What will the installation method be?

Hi,

Installing sockets, fan coils units in on ceilings, luminaires, and various spurs. The project is for an office, 3 floors of a building. Installing cables on tray. I'm a consultant so wasn't show these days how the cables will be installed in the walls, but i guess they'll be attached to the inner structure somehow, i doubt it will be it conduit.

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?

I was thinking of Table 4A2.

Doesn't help answer your question but, in my opinion, T&E is for house bashing not commercial installations.

Any reason you're not using singles?

4D2A

pww235 said:

T&E is for house bashing not commercial installations

Oh no it is not (well pantomime season is almost upon us) .

Seriously though T & E can and often is used in such. It is quite relatively cheap and readily available. Mapj1 gave some good pointers

Oh yes it is :)

It's cheap, true. But always rough as a badger's, especially in a commercial setting. It gets flung in and approximately zero care gets taken in terms of mechanical protection and adequate support. Do it properly and it may be ok, but that's a rare thing.

This is purely a personal take, I know it is technically permitted, but to my mind it shouldn't be outside the residential domain.


Also, need to watch out the undersized CPC doesn't fall foul of anyone's specification requirements. Just a watch point.

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.