Cable Tray

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Enile

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Hi all, I have two questions regarding cable trays.

I can size the cable tray with one of the four cases that NEC describes, but I think theres one case missing, and that is mixing cables from 1/0 up to 1000kcm.

For example, say I have 6-3/0 cables and 6-300kcm cables. I can assume that, by using the "equation":

A ? (1.1 Sd)

And making "Sd=0" (because theres no 1000kcm or bigger cables), I can use case 2.

Is that rigth? or how do you size the cable tray?

Also, NEC also states that if you bundle conductors they can be "installed in other than a single layer", so, if you dont want the ampacity increase by spacing them 2.15 times the OD, Can you place the bundled conductors without spacing and use 310.17 ampacities multiplied by 0.65?
 

patriot

Member
Location
Chapmansboro,Tn.
Hi all, I have two questions regarding cable trays.

I can size the cable tray with one of the four cases that NEC describes, but I think theres one case missing, and that is mixing cables from 1/0 up to 1000kcm.

For example, say I have 6-3/0 cables and 6-300kcm cables. I can assume that, by using the "equation":

A ? (1.1 Sd)

And making "Sd=0" (because theres no 1000kcm or bigger cables), I can use case 2.

Is that rigth? or how do you size the cable tray?

Also, NEC also states that if you bundle conductors they can be "installed in other than a single layer", so, if you dont want the ampacity increase by spacing them 2.15 times the OD, Can you place the bundled conductors without spacing and use 310.17 ampacities multiplied by 0.65?
If you run your wires in a triangle bundle with a,b,c phases together, you would multiply your largest cable by 2.15 and that will give you the space in between each bundle. Then you can figure your total width of your cable tray.
 

Enile

Member
I know that, the thing is:

Can I use a triangular formation without the space? (and of course using table 310.17 ampacities multiplied by 0.65)

The 2.15 rule its used if you want an ampacity increase...

About B-Line... it's a funny story, they actualy have a flow diagram to compute the width of the tray, but they do not take into consideration combining ONLY cables from 1/0 to 900KCM...

I'm leaning toward using the equation they give and make "SD=0"... but thats just redundant.. as if that were the case using only cables from 1/0 to 4/0 would use the areas of the cables as well not the diameters...

Hope to hear some more answers :).
 
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