I'm using twin and earth cables for a office building refurb. In the BS 7671 regs i can only see cable current carrying capacities for these cables in thermal ceilings and walls, this will not be the structure for the office building internally. How can i size the twin and earth cables? I.e are there alternative tables? I hope you can answer soon.
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.
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.
We're about to take you to the IET registration website. Don't worry though, you'll be sent straight back to the community after completing the registration.Continue to the IET registration site