Question to eletricians on ductbank replacement

[dahualin]

Our project has an existing duct bank which has about (18) 4" conduits in it. Since part of the duct bank is not deep enough for our project, we have to low that part for another 5'. I am thinking to add two manholes at each end of that part of duct bank and built new duct bank (lower) between two manholes. We have (7) 800A energized feeders in the duct bank to (7) different electrical rooms. We have to replace the feeder one at a time and keep others live. My questions are (1) how can we break the concrete encasement without breaking the PVC conduits in duct bank? (2) how can we figure out which two conduits have the set of cables for the same feeder before we break the PVC conduits?:?

We have to figure out the answers to the two questions. Then we maybe able to replace the feeder one at a time. Thank you all for your help.

 

[kingpb]

Ya better do the calcs for ampacity at that depth. Going deeper could very well mean less heat dissipation, and thus your circuits may hit 90 Deg C at a lower current.

 

[69gp]

I know the answer but hesitate to say how to do it here. All I will say is that you need to be qualified.

 

[starbolin]

I know the answer but hesitate to say how to do it here. All I will say is that you need to be qualified.

I'm curious. I too thought the OP was pretty sketchy ( especially the part about 'breaking' a 'vault' ), and I was happy to see the post slide of the bottom of the page, but the post got me wondering ( and since you dredged the post back to the top,) question is, doing a live switchover of circuits, circuits which are contained in a space too small for proper work clearances, is kind of outside what a normal EC does; what kind of qualifications would one need to A) redesign a cable vault, B) cut over live circuits, C) without switching provisions, and D) do so in a confined space? Am I correct in assuming it would be a matter of having sufficient hours doing that kind of work ( and a long pole ) or is that a ticket other than say a California G-10?

From a business standpoint I would think the game would be to have as many professionals as affordable sign off on the drawings and procedures such that the liabilities are spread as thin as possible? Or, charter yourself as a POCO and use hired guns to do the work?