Supporting MC cable with Cable Tray

[wwhitney]

The values in column 1 of Table 392.22(A) are just 7/6 * the width, rounded to the nearest 0.5". So I would stay that 42" wide tray would have an allowable fill of 49 sq in^2, and it would be unreasonable not to allow its use.

Cheers, Wayne

 

[Tainted]

The values in column 1 of Table 392.22(A) are just 7/6 * the width, rounded to the nearest 0.5". So I would stay that 42" wide tray would have an allowable fill of 49 sq in^2, and it would be unreasonable not to allow its use.

Cheers, Wayne

but how did you determine this? If it's not in the code, you can't really use that assumption, can you?

 

[wwhitney]

That's my judgement call, I would say extrapolation in this case is reasonable, and not allowing extrapolation would be unreasonable. AHJs may still be unreasonable.

As to determining that "the values in column 1 of Table 392.22(A) are just 7/6 * the width," it was by inspection. I.e. I calculated the ratios for each row, and noticed that most of them were 7/6. And the ones that weren't were the widths that aren't multiples of 6", and then the table entry just comes from rounding 1/3 and 2/3 both to 0.5.

Cheers, Wayne

 

[Julius Right]

2/0 awg 4 conductors MC cable overall diameter is 1.75 inches.

Then 55 cables present 130.78 inch^2.

If according Table 392.22(A1) in a 36 inches wide cable tray maximum 42 square inches is recommended you need 3 parallel tray of 3 feet and one of 1/2 feet.

Ladder or Ventilated Trough Cable Trays Containing Any Mixture of Cables.

A 1/2 feet may be reccomended as clearance between trays [in the same plane] that you need a total width of 5 feet.

 

[Julius Right]

If you will follow ANSI/NEMA WC 51 ICEA P-54-440 Tab.5-7 for a cable tray of 36" and 1.53" overall cable diameter you'll get 50 A for 55 cable in 2 layers [no space free].

 

[Julius Right]

Sorry. In my above post [#24] the total required width has to be 10.5 instead
of 5 fts.

 

[Julius Right]

If the grounding wire it is only #6 instead of 2/0 [4 of the same cross section area] then the overall diameter could be 1.53".Then 55 cables total area 55*1.53^2/4*pi()=101.12 square inch and the total width will be only 8.5 fts. You may put this in two plane keeping one foot [vertical clearance].

 

[Julius Right]

In Canada, the CEC rule 12-2200 details the requirements.

With cables less then 50mm in diameter in a tray, the minimum vertical clearance is 150mm between trays.

With cables greater then 50mm in diameter in a tray, the minimum vertical clearence is 300mm between trays.

Side clearence, to a wall or another tray, is 600mm where the width of the cable tray installation exceeds 1 m.

 

[Julius Right]

As I checked the maximum squareinch permissible according to NEC Art 392.22 A3 for solid bottom cable tray meet ANSI/NEMA WC 51 ICEA P-54-440 Tab.5-7 for 1.167 inch calculated depth.

 

[petersonra]

You mean something like this? I don’t see how a single
layer could ever be interpreted as “bundling”, especially with the larger sizes

I am not real familiar with the requirements for supporting MC cable but what is the point of putting that wire grid in if you have perpendicular strut already. Why not just support it off the unistrut and not mess with the wire grid.

 

[electrofelon]

I am not real familiar with the requirements for supporting MC cable but what is the point of putting that wire grid in if you have perpendicular strut already. Why not just support it off the unistrut and not mess with the wire grid.

I wired an old mill building once with exposed #1&#2 MC feeder cables attached to strut. In hindsight, I actually kinda like the idea of adding the wire mesh. It gets to be a lot of strut when you need them every 6 feet, and it takes a lot of fiddling around to get them all neat and parallel. Plus, depending on the location and occupancy, it provides some protection from people doing stupid things like hanging stuff on the MC. The one I did was marketed to artists and freaks so there were lots of parties there. We did box them in where they ran up walls, but they remained exposed on the ceiling.

 

[Jolted]

I wired an old mill building once with exposed #1&#2 MC feeder cables attached to strut. In hindsight, I actually kinda like the idea of adding the wire mesh. It gets to be a lot of strut when you need them every 6 feet, and it takes a lot of fiddling around to get them all neat and parallel. Plus, depending on the location and occupancy, it provides some protection from people doing stupid things like hanging stuff on the MC. The one I did was marketed to artists and freaks so there were lots of parties there. We did box them in where they ran up walls, but they remained exposed on the ceiling.

Yes, exactly. This building didn’t have any additional structural elements to anchor to either. In hindsight, MC was not a great fit in that building, it was just to tight. If I was doing it over, I’d bend EMT and pull wire.

 

[wwhitney]

So is the "wire mesh" a ladder type cable tray? (The portion on the right clearly has short sides, so it is a U-shaped cross section). Or is that a much beefier product, and this wire mesh something else?

Cheers, Wayne

 

[electrofelon]

So is the "wire mesh" a ladder type cable tray? (The portion on the right clearly has short sides, so it is a U-shaped cross section). Or is that a much beefier product, and this wire mesh something else?

Cheers, Wayne

Good question. At first I just thought it was just some commodity wire mesh product, but upon closer inspection I see it has upturned edges.

 

[Jolted]

So is the "wire mesh" a ladder type cable tray? (The portion on the right clearly has short sides, so it is a U-shaped cross section). Or is that a much beefier product, and this wire mesh something else?

Cheers, Wayne

We refer to it as basket tray most of the time, primarily gets used for low voltage wiring. Ladder tray is a different product

 

[KDough]

We also call it basket tray. And it is common to see it used as shown. Some contractors get a bit carried away with the number of M/C cables that they put on it. The pictures posted look to be ok, but I usually ask for the MII and that should give you a load limit per square foot or linear foot and a maximum distance between supports.. You would then take the weight of one foot of cable and figure how many pounds of cable per foot of tray to see if it is within the weight limit of of the tray.