Trenwa trench & Cable questions.

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69gp

Senior Member
Location
MA
Hi,

Just ran into an area that I am not to familiar with and wanted to see if I could get a little help here. I was on a project recently and seen multiple cables maybe 20- 2/0 2 conductor MC cables (weatherproof) grouped together emerging from the ground. These also are run through about a 15' section of Trenwa Trench. i have attached some pictures with the corresponding questions below each picture. I did try and find my answers in the code but it was a little confusing when I was reading section 300.5 (D)1

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Questions?

Should these cables be DE-rated since the are grouped together?
Also these cables run through a 15' section of Trenwa Trench system. Estimate that the Trenwa is filled to about 60% of the capacity. I could find no reference for Trenwa in the code for capacity only for cable tray. is there a code section for Trenwa?
Do these cables need physical protection when emerging from the ground? Although in this picture the cables are emerging near the leading edge of a panel these are still subject to mowers and weed whackers.



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Basically the same as above but this project is in New England. So the question of frost comes into play.
The way I see it when frost does occur it will push the cables up into the concrete cover for the Trenwa. Should these cables also be physically protected.
Finally I did look at the Trenwa site and all the photos I seen of the Trenwa had end plates or a complete wall system installed. With no end plate or cover is this an approved method?

aR-1tXG3UqEoRkUCuFXaeZWAV2jThMOaI796LlueEVs=w334-h187-p-no


When I read section 300.5 (D)1 my interpretation is that this is illegal. should these cables be physically protected with a conduit system?

thanks
 
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DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
Heh. I'm very interested in solar but I don't know much about how it's implemented, but is it possible that those cables are carrying the low-voltage dc current to a transformer/inverter?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Solar PV (except for off-grid battery systems) does not have low voltage DC. The panel to inverter connections can be up to 1000VDC in non-residential systems. (OK, that is still low voltage rather than MV, but I do not think that is what you meant.)
 

69gp

Senior Member
Location
MA
Heh. I'm very interested in solar but I don't know much about how it's implemented, but is it possible that those cables are carrying the low-voltage dc current to a transformer/inverter?


The system is a 1000 volt DC.
 

DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
Yeah. And I already knew that too. I remember a change to the 2014 nec regarding the 600/1000 volt scope because of pv systems. In that case, holy carp those cables are dangerous!
 

kenaslan

Senior Member
Location
Billings MT
I am also using Trenwa however in a different application. 6 sets of 350 MC-HL 4160V in a joint Trough.

A trough (or a trench) is understood as a long shallow rectangular-shaped excavation, where the walls, bottom and cover are made of concrete. The cables can be installed on the floor, hanging from supports on the walls or racks or cable tray mounted inside. The trough can be filled with a material with good thermal properties or it can be left unfilled (air filled). The heat transfer mechanism is different for filled and unfilled troughs and therefore they are treated independently.

The Cable manufacture told me to use a program called CYMCAP. Have yet to use it but is is found here. http://www.cyme.com/software/cymcap/
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
Those cables are protected, they look like armored multi-core cable; I assume they are rated for direct burial.

In the first picture, I might question the disconnect box laying horizontal with handle up. Water intrusion? Would like to see rating of enclosure for that.
 
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69gp

Senior Member
Location
MA
Those cables are protected, they look like armored multi-core cable; I assume they are rated for direct burial.

In the first picture, I might question the disconnect box laying horizontal with handle up. Water intrusion? Would like to see rating of enclosure for that.

those are DC combiner boxes and they are rated to be mounted like that.
As for the protection back fill around here has always been sand. not loam with stones mixed in. Also I do not think the cable rubbing against the cover will last long with frost heaves in the cols months.
 
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