G
Gohanto
Hi all, I'm an ELV consultant (mostly sound and video systems for hotels, theatres, schools, etc. all commercial projects and mostly new construction) and relocated about a month ago from the US to UAE (which follows UK electrical standards and practices as far as I can tell. I've gotten up to speed on most of the changes in the UK market for design containment systems for ELV here, but the one I'm still working on is overhead trunking.
From what I've gathered, overhead trunking is generally used when conduits larger than 32mm are needed (unlike the US where conduits up to 100mm are used). In a school for example, steel trunking may run above the ceiling of a hallway, and all the individual power circuit conduits for each classroom terminate into that trunking, instead of running each small conduit back to the DB. (In the US, we'd show a single junction box above the ceiling outside each classroom where all the classroom conduits terminate into, then connect those junction boxes with large conduits back to the equipment rack room. Alternatively we use cable tray, but only if the ceiling is ACT / Removable tiles).
Assuming I've understood the basics correctly, I have a couple questions I'm looking for help with
- How do you draw-in cables with such as system, especially when conduits terminates into trunking at various locations above a ceiling? (I think of draw-in as pulling every cable you need at once, point-to-point between junction boxes. Any conduit tap-off seems like a hard 90-degree turn with no bend to prevent cable insulation from scratching off)
- Since overhead trunking has a lid on the top of it, no draw-in boxes are required like conduit does. So how does cable draw-in work if the trunking lid is facing upward? (I've always assumed 2 main teams for cable draw-in, one at the DB feeding cables in, one at the next junction box pulling cables from the floor, and the junction box always opens downward toward the floor so it's pretty easy)
- Is trunking primarily used for power here, or does anyone see it used here for loudspeaker and video cable containment as well?
- I've been various spec's, but it seems like draw-in boxes are required every 9m or every 2, 90 degree bends in conduit. Does anyone know where that requirement came from? (In the US, draw-in boxes are spaced every ~30m, so I'm curious)
Sorry for the long post, but thanks for any help!
From what I've gathered, overhead trunking is generally used when conduits larger than 32mm are needed (unlike the US where conduits up to 100mm are used). In a school for example, steel trunking may run above the ceiling of a hallway, and all the individual power circuit conduits for each classroom terminate into that trunking, instead of running each small conduit back to the DB. (In the US, we'd show a single junction box above the ceiling outside each classroom where all the classroom conduits terminate into, then connect those junction boxes with large conduits back to the equipment rack room. Alternatively we use cable tray, but only if the ceiling is ACT / Removable tiles).
Assuming I've understood the basics correctly, I have a couple questions I'm looking for help with
- How do you draw-in cables with such as system, especially when conduits terminates into trunking at various locations above a ceiling? (I think of draw-in as pulling every cable you need at once, point-to-point between junction boxes. Any conduit tap-off seems like a hard 90-degree turn with no bend to prevent cable insulation from scratching off)
- Since overhead trunking has a lid on the top of it, no draw-in boxes are required like conduit does. So how does cable draw-in work if the trunking lid is facing upward? (I've always assumed 2 main teams for cable draw-in, one at the DB feeding cables in, one at the next junction box pulling cables from the floor, and the junction box always opens downward toward the floor so it's pretty easy)
- Is trunking primarily used for power here, or does anyone see it used here for loudspeaker and video cable containment as well?
- I've been various spec's, but it seems like draw-in boxes are required every 9m or every 2, 90 degree bends in conduit. Does anyone know where that requirement came from? (In the US, draw-in boxes are spaced every ~30m, so I'm curious)
Sorry for the long post, but thanks for any help!