Electrical Cable Trenches (Question)

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rasssawiii

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Hi all,

It is a question regarding the electrical cable trenches ..

We are building a new petrochemical complex and the plan is to have all cable routing underground in concrete trenches. There will be dedicated trenches for LV cables and dedicated ones for MV cables.

The question here, is there any restriction on the maximum number of tiers allowed? Please explain technically the reasons of the restriction

Another question, is it allowed to have LV & MV cables in the same trench? If yes, what would be the best arrangement of the cables?

Thanks.
 
Re: Electrical Cable Trenches (Question)

Originally posted by rasssawiii:

Another question, is it allowed to have LV & MV cables in the same trench? If yes, what would be the best arrangement of the cables?
Click to expand...
Allowable, yes. Advisable, no.
 
Re: Electrical Cable Trenches (Question)

pierre..
Thanks.
But I could not find the answer of my question.


bdarnell..
Thanks
 
Re: Electrical Cable Trenches (Question)

Pierre,
This is not a duct bank that is buried. It is an open trench, often with layers of cable tray. I don't think that there is any code rule that covers this type of installation. I think that the best way would be to use the cable tray rules as that is the closest NEC installation method. The one main difference that I can see is the reduced ventilation around the conductors as a result of the trench side walls and top cover.
Don
 
Re: Electrical Cable Trenches (Question)

I don't know what these "trenches" would look like, nor whether they would constitute a "raceway" (i.e., "an enclosed channel of . . . nonmetallic materials . . ."). But it may be worth taking note of 300.3(C)(2).
 
Re: Electrical Cable Trenches (Question)

I myself have not worked in a petrochemical environment, so I am not familar with that type of trench... I took a stab at it. I have seen a "preformed" concrete trench with bus duct in it, but not cable tray.


Charlie
to elaborate on your post maybe 300.3(B) would help give some direction as well.
 
Re: Electrical Cable Trenches (Question)

I think that this is just one of a number of common industrial practices that are not in the NEC.
Don
 
Re: Electrical Cable Trenches (Question)

You might also note that below-grade trenches, depending on the routing, may be classified as Class 1, Div 1 locations in a petro-chem environment (as opposed to Div 2 or non-haz).
 
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