manhole, duct bank, medium voltage stuffs

[anbm]

can someone enlight me?

1. When do we need to use duct bank to run conduits?
2. Is there any specific rules to size duct bank?
3. Can we run power and telecom conduits in same duct bank?
4. When do we need to use manhole, what's typical spacing between manholes?
5. How do we size and spec medium voltage cable, fuse, breaker as setting its relay, is there any free sources to learn about medium voltage stuffs and design?

Thanks a bunch,

TX-man

 

[davidbeach]

It all just depends. This is not something this is you can pick here, you really need to learn from a mentor, studying projects and what works well and what not so well. But a few hints:

1. A duct bank is just a collection of conduits.
2. Large enough. Both in individual size and quantity. 5 years from now nobody will say you had too many spares, but they may curse you for not enough spares.
3. With enough separation; follow applicable rules. In North American the NESC or local equivalent should guide. Standards and requirements of relevant utilities will also govern.
4. So the runs aren't too long to pull.
5. Properly and per code, find a mentor. Lots of reading material in faq238-1287.

 

[7anoter4]

Hi tx-man
I think davidbeach expressed almost all about cable ducts. What I intend to do is to draw some lines from my experience.
The duct bank is a concrete block including plastic [usually PVC] pipes of 4-6" dia. [usually 6"] and a few [1-4] steel [or cast iron] pipe of the same dia. The steel pipe is dedicated to telecommunication and instrument cables and plastic pipe for power and control cables [the steel pipe will be at least 12 inches above the power cables].
The pipes are arranged in rows and columns on a plastic support prior to pour the concrete. In order to avoid a magnetic closed circuit around the power cable pipes [mainly if there are single phase cables] no reinforced steel is permitted between pipes. A steel reinforcing [a wire net of 10 gauge] is indicated along the duct bank periphery. The minimum clearance between pipes is 3" in order to facilitate the concrete penetration.
A manhole is required if the duct bank lentgh is more than 100-150 ft long or for any cross encountering other duct bank.From manhole conduits get up to the equipment connected with the cables [located usually]above the ground level.
The manhole has to be at least 10 feet height 10 feet long and 10 feet wide, provided with some kind of ladder and connection to grounding grid.The cables should layed on cable trays-the instrument cable tray should be covered and solid bottom cable trays.
Best Regards