Comms/Power Vaults

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FaradayFF

Senior Member
Location
California
Greetings,
Does anyone know reasoning behind why an underground concrete duct bank comes into two separate vaults/MHs before entering a building? Since we typically run one duct containing communications and power conduits, why would we have two separate vaults? Why not have a single vault?

I was just curious, this seems like a standard industry practice.

Thanks,
EE
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
I may be missing something here but here goes...


800.133?
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
I've not seen "ducts within a duct", normally power and communications conduits are run separately around here at least. I would hazard a guess and say that the answer to your question is that the conductors/cables emerge from their conduits in the vaults so separate ones are needed to separate power from LV? Dunno, I've never see what you are talking about.

-Hal
 

FaradayFF

Senior Member
Location
California
I meant that there is a separate vault/PB for electric conduits and communications conduits. Even if the said conduits are part of the same concrete encased duct bank. When these conduits emerge into their separate pull boxes before entering a building, power and comms conduits are not routed through a shared pull box.

Thanks for your replies.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
I meant that there is a separate vault/PB for electric conduits and communications conduits. Even if the said conduits are part of the same concrete encased duct bank. When these conduits emerge into their separate pull boxes before entering a building, power and comms conduits are not routed through a shared pull box.

Thanks for your replies.

Didn’t think they were supposed to be...
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Aren't they run in separate conduits within the concrete encased ductbank? Don't the cables or conductors emerge from those conduits in the pull boxes? You do realize that you can't have line voltage and LV in the same enclosure. Or is there something I'm missing?

-Hal
 

Douglas Gordon

New User
Location
Vancouver BC Canada
Occupation
Fibre Optic Project Manager
Yes,

Communications and electrical are run as two completely separate systems. This way you do not have to come into contact with electricity (high voltage) when running communications cables (low or no voltage). While ticketed electricians are required to work on electrical systems, it is not a requirement to be certified (but I would hope at the very least qualified) in order to work in fibre optics or even copper communications lines. You are not permitted to run comm cables in the same ducts as electrical cables, however I have heard you could sub duct a conduit in order to encase and protect a fibre optic cable. I suppose the danger is if the cable were to become electrified, for whatever reason, and was not properly grounded, a technician working further down could get hurt. Also, more with coaxial cable (copper cables) than fibre optics, the cable can experience induction by running in parallel with an electrical cable and this can cause data (a signal from the internet) to become corrupt.

So I think the answer is: national electrical code makes it illegal to build things contrary to guidelines. If you do build out of specification, (with communications that isn't inspected - hydro probably is everytime) you probably won't hear about it... Unless someone does happen to die from electrocution and then the prime contractor's CEO will go to jail for 10 years.

Or maybe not.
 
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