sizing a trough

[carrierman]

I am a little rusty in this area. I am running a new service to a new building and we want to come up thru the floor into a trough then up into the panel . the trough is needed for splices so we can get the wire size down to fit into a 200 amp panel. we will be bringing 2 four inch pvc conduits up into the trough along with a third one for a spare. Wire size coming in will be parallel 350's due to 500 foot run and voltage drop. How do I size this trough? Thank you for any and all help./

 

[electrojet]

Splice box or Trough

Splice box or Trough

Per the NEC code 314.28 Pull and Junction Boxes for 600v or less....

314.28 A2 sez - where splices or where angle or U pulls are made, the distance between each raceway entry inside the box and the OPPOSITE wall of the box shall not be less than six times the (trade Size) of the largest raceway in a row PLUS the distance shall be increased for additional entries by the amount of the sum of the diameter of ALL other reaceway entries in the SAME row on the SAME wall of the box.

So, your three 4" conduits would be calculated as 4x6= 24" Plus 4" + 4"= for the second and third conduits for a total of 32" ........ That gives the distance from the entry wall of the three 4" feed conduits to the OPPOSITE wall of the gutter.....LENGTH....

Next you will have to know what conduits will be on the wall leaving the trought to the 200 amp panel ( which you did not state) i.e. the adjacent wall, and apply the same calculation to get the WIDTH of that side of the gutter. That will give you the SECOND side of the box dimension.

So once you determine the Length and Width there are standard depths of gutter boxes as I remember....

You should also refer to section 366 in the code book especially 366.56 which deals with Splices within Gutters as there is a statement that "conductors including splices and taps shall not fill the gutter to more that 75% of its area."

Hope this helps a little//


Electro Jet

 

[hardworkingstiff]

JB will be bigger than the panel.

 

[Pierre C Belarge]

Troughs (wireways are traditionally incorrectly sized) are the standard procedure for this type of installation. My suggestion is to use a Jbox instead. Depending on how you enter the trough, it may need to be substantially longer than 32 inches. Art 312 is also important in sizing troughs.
I understand you will not have too many conductors, but distance between raceway entry and the depth of the trough may make this a tough install.