cable tray questions

[jparker83]

I was going through my NEC handbook (2005 edition) and was trying to find out if there is a limit on how many bends a cable tray can do before it is against code.

I have gone through Article 342 and have not found any mentioning about number of bends, unless my eyes deceive me. Can anyone verify this or is it going to be like conduit only 360??

Thanks

 

[weressl]

I was going through my NEC handbook (2005 edition) and was trying to find out if there is a limit on how many bends a cable tray can do before it is against code.

I have gone through Article 342 and have not found any mentioning about number of bends, unless my eyes deceive me. Can anyone verify this or is it going to be like conduit only 360??

Thanks

The Code does not limit, however on the practical side you should be calculating and/or measuring pulling forces on larger cables for complex runs.

 

[cycotcskir]

Think of tray as having an unlimited amount of pulling points. As already stated, if you are pulling large cable or long runs, be careful of the tension and amount of turns. Many pulleys and rollers help here, along with a tugger with a guage. If you are pulling small wire, use multiple pull points and you can have 1080+ derees of bend with no harm.

 

[rbalex]

The Cable Tray Institute, on its "Technical Bulletins" and "Codes and Standards" pages, lists several application and installation guildelines both for trays and cables. The "Codes and Standards" page also links to NEMA Standard VE-2 which gives more specific instructions. VE-2 is a free download from NEMA. Virtually every major Cable Tray manufacturer is an Institute member.

 

[cycotcskir]

Nice PDF, thanks

 

[tom baker]

A cable tray is a support system, not a raceway.

 

[Ranch]

Maximum distance between gear and cable tray

Maximum distance between gear and cable tray

Re: Maximum distance above gear a cable tray can be practically installed. I don?t think it?s in the NEC (correct me if I am wrong), but it impacts support requirements and my concern today is lateral support.

Specifics: MCC, low voltage, 90? tall. With 24? ladder type cable tray to be hung above

In preliminary design, this tray could wind up 40? above the MCC, and with a handful of size 5 starters, those water-falling power conductors would most certainly contribute to undesirable lateral deflections in the absence of a support system preventing side to side movement. Furthermore, it will cause a structure to become so tall, it will be difficult to transport across two US states.

I am trying to build a case to lower this tray and thus the structures roof to a practical height. Does anyone know if in fact there is a code, guideline or something on this to help me build my case?

 

[Ranch]

Maximum distance between gear and cable tray

Maximum distance between gear and cable tray

I guess another aspect to my post above would be: How far can a tray cable drop before it requires support?

 

[weressl]

Re: Maximum distance above gear a cable tray can be practically installed. I don?t think it?s in the NEC (correct me if I am wrong), but it impacts support requirements and my concern today is lateral support.

Specifics: MCC, low voltage, 90? tall. With 24? ladder type cable tray to be hung above

In preliminary design, this tray could wind up 40? above the MCC, and with a handful of size 5 starters, those water-falling power conductors would most certainly contribute to undesirable lateral deflections in the absence of a support system preventing side to side movement. Furthermore, it will cause a structure to become so tall, it will be difficult to transport across two US states.

I am trying to build a case to lower this tray and thus the structures roof to a practical height. Does anyone know if in fact there is a code, guideline or something on this to help me build my case?

We use the bending radius of the largest cable as a design guideline.

As far as lateral bracing goes, seizmic requirements and pulling forces - when pulleys are directly atatched tot he cable tray - could require structural engineering overview.

 

[Smart $]

I guess another aspect to my post above would be: How far can a tray cable drop before it requires support?

If it is supported, it won't drop :grin:

On the serious side on the discussion, I'm getting the impression you are looking at putting a tee in the tray run, then a "waterfall" 90 to drop into the MCC. In this situation we would add another piece of straight tray all the way to the top of the MCC and use 90? angle brackets to secure it thereto. Environmental conditions dictate how the cable penetration into the MCC is made.

However, more typically we just run the tray directly over the MCC and drop the cable out of the tray bottom if it is small enough. If not, sometimes a rung is cut out to accommodate the cable's bending radius. Depending on the circumstances, some cables will have to go over the side. For exceptionally long drops, we will run either tray (straight) or conduit up from the MCC.

I've been on installations where we had stacked tray runs both above and below the gear.

 

[cycotcskir]

How far can a tray cable drop?

Until it hits the ground:smile:

 

[Ranch]

I think we have talked them out of dropping multitudes of control and power cabling from four feet down to a foot. It is a pretty serious consideration, getting the cables where they need to go.

Thanks Holtsters . .. . (esp. to Smart $)

 

[weressl]

I think we have talked them out of dropping multitudes of control and power cabling from four feet down to a foot. It is a pretty serious consideration, getting the cables where they need to go.

Thanks Holtsters . .. . (esp. to Smart $)

Will that leave room for proper bending radius for all sizes, including the required cable gland(CGB or similar) height installed on top of the MCC?

 

[Ranch]

Will that leave room for proper bending radius for all sizes, including the required cable gland(CGB or similar) height installed on top of the MCC?

Yes - no big cables, no big glands. Project starts tomorrow, with some intelligent forethought thanks in part to the Holtsters.

Sometimes making "overly" sure you have enough can lead to problems from having too much

 

[weressl]

Yes - no big cables, no big glands. Project starts tomorrow, with some intelligent forethought thanks in part to the Holtsters.

Sometimes making "overly" sure you have enough can lead to problems from having too much

As long as you are sure larger cables will 'never' be installed in the future.

What is the saying? Never say 'never'?