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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!
 
I'd have thought (and I may be wrong here) that basket tray or perforated cable tray would make this hell of a lot easier, Simply lay the cables in (neatly), It's also quite common to have 2 or more runs of tray, 1 for LV and another for data/comms/fire etc. Its certainly something I've seen and used more of than trunking above the ceiling. Although I'm sure someone with more experience will be along shortly
 
Generally commercial containment will be trunking and conduit for small power, tray for larger power, ladder for very big power, a basket/tray for fire alarms and then further baskets for everything else
 
I'd have thought (and I may be wrong here) that basket tray or perforated cable tray would make this hell of a lot easier, Simply lay the cables in (neatly), It's also quite common to have 2 or more runs of tray, 1 for LV and another for data/comms/fire etc. Its certainly something I've seen and used more of than trunking above the ceiling. Although I'm sure someone with more experience will be along shortly

How do you draw-in cable using baskets though? I like cable baskets and use them frequently, but I've never tried used them above a non-accessible ceiling before (e.g. Plaster). Most cables typically slide pretty easily through straight and curved pieces of conduit, but it's difficult to believe cables would slide just as easily on top of baskets, especially if there are any turns involved. That said I've never tried do this.

Or is it simply a matter of installing a lot of access panels everywhere in the ceiling along the length of the cable basket?
 
How do you draw-in cable using baskets though? I like cable baskets and use them frequently, but I've never tried used them above a non-accessible ceiling before (e.g. Plaster). Most cables typically slide pretty easily through straight and curved pieces of conduit, but it's difficult to believe cables would slide just as easily on top of baskets, especially if there are any turns involved. That said I've never tried do this.

Or is it simply a matter of installing a lot of access panels everywhere in the ceiling along the length of the cable basket?

It comes down to why you're using said containment, would it be added to at a later date or is it to meet fire safety regulations to maintain cabling in place in escape routes...etc etc.
 
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How do you draw-in cable using baskets though? I like cable baskets and use them frequently, but I've never tried used them above a non-accessible ceiling before (e.g. Plaster). Most cables typically slide pretty easily through straight and curved pieces of conduit, but it's difficult to believe cables would slide just as easily on top of baskets, especially if there are any turns involved. That said I've never tried do this.

Or is it simply a matter of installing a lot of access panels everywhere in the ceiling along the length of the cable basket?

The simple answer is that you install the cable before its plastered.

The installation needs to be suitably designed to fulfill what is required of it. If it needs to be readily accessible for future alterations then it needs to be designed that way.
There is no universal, one size fits all, answer.
 

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