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Design Practice vs Code Required qty of MV Cables in a Manhole

Design Practice vs Code Required qty of MV Cables in a Manhole

Design Practice vs Code Required qty of MV Cables in a Manhole

(OP)
Is there a Code which suggests how many MV Cables (15kV) are allowed to transit a manhole? I would assume there are some limiting code requirements? Manhole fires are costly and are not appreciated by end users. I am looking for codified reasons to have parallel MV duct systems to deliver reliabe power. IEEE 493 is the only source I have found thus far.

RE: Design Practice vs Code Required qty of MV Cables in a Manhole

I don't think there are any Code requirements.  It is a matter of economics and reliability.  You should consider fireproofing if there are multiple circuits in the manhole.
 

RE: Design Practice vs Code Required qty of MV Cables in a Manhole

Don't know of code reasons but have seen utility standards that allowed only one circuit.
If you have two circuits in one vault and one goes bad how do go ( or send some one)   in and fix it?
I would not send a lineman into a vault to repair or repull a circuit while the other circuit was energized. When people are in there moving things around, bumping into things dropping tools etc.  ( all the things they are not supposed to do) is when cables fail.
I would rely on NFPE 70E.  There is a potential arc-flash in there.
Draw eveloped sections of your vaults, pick a vault ( for 500 or 750 KCMIL a 5'x &' is the smallest I would use. Detail your supports, routing, splices, and pulling. Consider your bending radius and getting the "bite" in the vault if you pull out and in again.
Safety is one issue.  The other is economics.  
Google up the Belliagos fire in Las Vegas.  Two circuits in one vault, the fire shut down the hotel and casino for a week and cost about 30 million dollars in revenue.

RE: Design Practice vs Code Required qty of MV Cables in a Manhole

I agree with jghrist there is not a Code limiting the number of the cables in a manhole.
Usually the cables are running on a cable tray through the manhole so you can see the article of regulations of cables on cable tray. The manhole has to be large enough to facilitate cable bending and to permit cable visiting safety.
For cable ampacity you may follow the NEC recommendations or ICEA P-54-440 /NEMA WC51-2003 recommendations. See:
http://www.icea.net/Public_Pages/Documents/NEMA_Power_Cable_Standards.html
"Ampacities of Cables in Open-Top Trays (Rev. 1, 2003)"
But this ampacity is more than permitted for adjacent cable duct, any way.
 

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