Cable tray sizing

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fandi

Senior Member
Location
Los Angeles
Hello All,
We need to run a 2000A 480V connection between the switchboards inside a building. Because of tight space going up from one floor to the above floor, the contractor suggests to use cable tray instead of conduit. Is it true that cable tray is more flexible than conduit? I think one of the reason is the bend radius of (5) sets of 4"C for 2000A connection.
If cable tray to be used, how do I size it? I read somewhere that 50% fill is max.
Last, is there any other concern about running cable tray, for example ground fault protection, etc.?
Thanks.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
I think you'll find that cable tray fill is probably closer to 20% max... but it really isn't based on percentage... it's based on conductor or cable widths or CSA and tray width (so it doesn't matter if you use 4" or 6" rail tray, the max fill across the tray will be the same).

I suggest you familiarize yourself with Article 392 then come back and ask questions... or better yet, go look at some actual installations of cable tray. ;)
 
C

Carultch

Senior Member
Location
Massachusetts
fandi said:
Hello All,
We need to run a 2000A 480V connection between the switchboards inside a building. Because of tight space going up from one floor to the above floor, the contractor suggests to use cable tray instead of conduit. Is it true that cable tray is more flexible than conduit? I think one of the reason is the bend radius of (5) sets of 4"C for 2000A connection.
If cable tray to be used, how do I size it? I read somewhere that 50% fill is max.
Last, is there any other concern about running cable tray, for example ground fault protection, etc.?
Thanks.
Click to expand...


There's a nice flowchart in this document.
http://www.cooperindustries.com/con.../cable_tray_systems/all_products/CTManual.pdf

The one blindspot it has, is that listed PV wire of all sizes can be installed in cable tray. Nowhere does NEC say what the applicable tray sizing and ampacity constraints are, for this application. 50% fill is probably the most you can physically do, although it is extremely ambitious.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
Carultch said:
....The one blindspot it has, is that listed PV wire of all sizes can be installed in cable tray. Nowhere does NEC say what the applicable tray sizing and ampacity constraints are, for this application.
Click to expand...
Where does it say listed PV Wire can be installed in Cable Tray?

...or is listed PV Wire one of those that qualify under the generic category of "Other factory-assembled, multiconductor control, signal, or power cables that are specifically approved for installation in cable trays"?
 
C

Carultch

Senior Member
Location
Massachusetts
Smart $ said:
Where does it say listed PV Wire can be installed in Cable Tray?

...or is listed PV Wire one of those that qualify under the generic category of "Other factory-assembled, multiconductor control, signal, or power cables that are specifically approved for installation in cable trays"?
Click to expand...

That's an NEC2014 requirement. 690.31(C)(2)
 
Smart $

Smart $

Esteemed Member
Location
Ohio
Carultch said:
That's an NEC2014 requirement. 690.31(C)(2)
Click to expand...
I think they forgot to correlate that one with Article 392.... :happyyes:

And what is the purpose of the Informational Note? Conduit fill calculations have nothing to do with tray fill calculations. :huh:
 
Julius Right

Julius Right

Senior Member
Occupation
Electrical Engineer Power Station Physical Design Retired
In my opinion, you could follow NEC Art. 392 [392.80 Ampacity of Conductors.].
However, at first you have to check the available space[possible width and height of a tray], the location-usually some 10 inches under the ceiling it is to keep [or under the ceiling beams] at least 7-8 ft. above the floor-inside location and the required cable tray type: ladder, ventilated, solid bottom open top, covered or raised cover provided, or else. Also the material is important: galvanized steel , fiberglass reinforced polyester or else.
The vertical riser tray has to be closed all around up to 6 ft. above the upper floor in order to protect the cables. A sort of cable grips hanger has to be provided and the floor opening has to be sealed against fire and smoke by a means of fire stop. No further derating is required if the cable tray is covered not more than 6 ft.
 
F

fandi

Senior Member
Location
Los Angeles
Julius Right said:
In my opinion, you could follow NEC Art. 392 [392.80 Ampacity of Conductors.].
However, at first you have to check the available space[possible width and height of a tray], the location-usually some 10 inches under the ceiling it is to keep [or under the ceiling beams] at least 7-8 ft. above the floor-inside location and the required cable tray type: ladder, ventilated, solid bottom open top, covered or raised cover provided, or else. Also the material is important: galvanized steel , fiberglass reinforced polyester or else.
The vertical riser tray has to be closed all around up to 6 ft. above the upper floor in order to protect the cables. A sort of cable grips hanger has to be provided and the floor opening has to be sealed against fire and smoke by a means of fire stop. No further derating is required if the cable tray is covered not more than 6 ft.
Click to expand...
Thanks, Julius.
 
F

fandi

Senior Member
Location
Los Angeles
The cable to be used in this case is (5) sets of 4#600kcmil & 1#1 GND. Two sets will be right up against the side rails and the other three sets will be in the middle.
I only have two more questions to determine cable tray width:
- How do we determine the gap between each set?
- What is allowable cable fill area and its column 1 in table 392.22(A)? Let's say if a 36" cable tray to be used, the column 1 reads 42 square inches but what does that mean?
Sorry for being such a newbie.
Thanks.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
fandi said:
The cable to be used in this case is (5) sets of 4#600kcmil & 1#1 GND. Two sets will be right up against the side rails and the other three sets will be in the middle.
I only have two more questions to determine cable tray width:
- How do we determine the gap between each set?
- What is allowable cable fill area and its column 1 in table 392.22(A)? Let's say if a 36" cable tray to be used, the column 1 reads 42 square inches but what does that mean?
Sorry for being such a newbie.
Thanks.
Click to expand...
Are you certain you are using multiconductor cable? The #1 GND in each cable presents a 250.122(F) grounding issue.

You will have to obtain either diameter or fill data from cable manufacturer's documentation.
 
F

fandi

Senior Member
Location
Los Angeles
total OD of each set is 1.024 x 4 + 0.435 = 4.531” so roughly 4.6”. If the gap is 3", the width should be 5 x total OD of each set + 4 x gap between sets
= 5 x 4.6 + 4 x 3 = 35" so the 36" tray should be used, correct? But I still haven't got a chance to use Column 1 table 392.22(A).
 
Smart $

Smart $

Esteemed Member
Location
Ohio
fandi said:
total OD of each set is 1.024 x 4 + 0.435 = 4.531” so roughly 4.6”. If the gap is 3", the width should be 5 x total OD of each set + 4 x gap between sets
= 5 x 4.6 + 4 x 3 = 35" so the 36" tray should be used, correct? But I still haven't got a chance to use Column 1 table 392.22(A).
Click to expand...
Where are you getting these numbers and equations???

If you are using multiconductor cable, you have to get the diameter from manufacturer's documentation. It'll be one number (diameter) for each set.
 
F

fandi

Senior Member
Location
Los Angeles
Smart $ said:
Are you certain you are using multiconductor cable? The #1 GND in each cable presents a 250.122(F) grounding issue.

You will have to obtain either diameter or fill data from cable manufacturer's documentation.
Click to expand...
Smart,
I could well be wrong but I think 250.122 (F) allows me two options for this 2000A connection:
- One single EGC for entire 2000A cable connection.
- Each EGC in each set.
This is how I came up with (5) sets of 4#600kcmil & 1#1 EGC:
I treat the 2000A as (5) sets of 400A, hence 4#600kcmil. And since 600kcmil is being used, the according EGC is #1 per Table 250.122.
Please advise. Thanks.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
fandi said:
Smart,
I could well be wrong but I think 250.122 (F) allows me two options for this 2000A connection:
- One single EGC for entire 2000A cable connection.
- Each EGC in each set.
This is how I came up with (5) sets of 4#600kcmil & 1#1 EGC:
I treat the 2000A as (5) sets of 400A, hence 4#600kcmil. And since 600kcmil is being used, the according EGC is #1 per Table 250.122.
Please advise. Thanks.
Click to expand...
Simple question... are you using multiconductor or single conductor cable?

I (and the NEC) don't care how you treat the 5 sets of 4#600. What matters for cable tray sizing is whether the conductor sets are cabled by a manufacturer or single conductors per manufacturer and perhaps "cabled" by installer... or not.

And in the interest of saving time, please specify manufacturer and cable type.
 
J

johnmeto

Banned
Location
US
The one blindspot it has, is that recorded PV wire of all sizes can be introduced in link plate. No place does NEC say what the relevant plate measuring and ampacity imperatives are, for this application.
 
F

fandi

Senior Member
Location
Los Angeles
Smart $ said:
Where are you getting these numbers and equations???

If you are using multiconductor cable, you have to get the diameter from manufacturer's documentation. It'll be one number (diameter) for each set.
Click to expand...
Smart,
From Southwire Simpull THHN cutsheet Product Specifications at the end of this page:
http://www.southwire.com/products/SIMpullTHHNCable.htm
600kcmil OD = 1.024"
#1 OD = 0.435"
I still don't know the minimum gap between the sets. I guess the rule of thumb is the gap should be equal the total OD of each set.
 
F

fandi

Senior Member
Location
Los Angeles
Smart $ said:
Simple question... are you using multiconductor or single conductor cable?

I (and the NEC) don't care how you treat the 5 sets of 4#600. What matters for cable tray sizing is whether the conductor sets are cabled by a manufacturer or single conductors per manufacturer and perhaps "cabled" by installer... or not.

And in the interest of saving time, please specify manufacturer and cable type.
Click to expand...
Smart,
From Southwire Simpull THHN cutsheet, it's single conductor.
The cable rep suggests me to use MC cable to reduce the cable tray width from 36" to 24".
 
F

fandi

Senior Member
Location
Los Angeles
Ok the EGC for the 2000A connection should be #250kcmil. And I only need 1#250kcmil for the cable tray per Section 250.122 (F). And table 392.22 (B) (1) Column 1 should be used as it's single conductor. I first need to add all the area in square inches and use Column 1 to cross reference the correct cable tray width.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
fandi said:
Ok the EGC for the 2000A connection should be #250kcmil. And I only need 1#250kcmil for the cable tray per Section 250.122 (F). And table 392.22 (B) (1) Column 1 should be used as it's single conductor. I first need to add all the area in square inches and use Column 1 to cross reference the correct cable tray width.
Click to expand...
Sounds like you are making progress... :thumbsup:

Note there is no specific "gap" required, but you will have to keep each set together (conductors immediately adjacent to each other).

MC cable has a wider diameter than THHN in single conductor... so that'll not save you anything on width.

Multiconductor MC may save you width, but you then have the handling issues... 4C/600kcmil MC is no picnic getting in tray.
 
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