Cable tray

[dm9289]

I have been doing a MH 2017 course and it seemed a bit limited with cable tray calcs.
I searched the web for step by step resources regarding how to determine spacing and when you can stack or have to separate ( no luck on web) Im having difficulty understanding the 3 condition of 392.22(1)(a-b-c) and the "SD" in table 392.22(A).

I have to get my car from inspection so I will be away for a while any resources you know of would be appreciated. Im trying to gain understanding not doing a project.

Thank you
Dave

 

[augie47]

The Cable Tray manufacturers all have informative booklets that guide you such as

http://www.eatoncorp.com/content/dam/eaton/products/support-systems/cable-management/b-line-cable-tray-design-considerations.pdf

They also have on-line calculator programs that might prove helpful.

 

[dm9289]

The Cable Tray manufacturers all have informative booklets that guide you such as

http://www.eatoncorp.com/content/dam/eaton/products/support-systems/cable-management/b-line-cable-tray-design-considerations.pdf

They also have on-line calculator programs that might prove helpful.

there was some good info there but none involving use of 392(A)(1)(c).

It however was helpful and thank you

 

[Simion Sacrol]

I have a question on cable trays. The NEC states that all metal cable trays have to be grounded. What if the cable tray is screwed to imbedded strut in a concrete trench in direct contact with the earth? would you have to ground that metal cable tray? It is being used to hold power 480, 120 and low voltage conductors which are in cable tray rated conductors.

 

[Julius Right]

In my opinion , the cables of less than 4/# conductor have to be bundled together as per attached sketch

 

[steve66]

I have a question on cable trays. The NEC states that all metal cable trays have to be grounded. What if the cable tray is screwed to imbedded strut in a concrete trench in direct contact with the earth? would you have to ground that metal cable tray? It is being used to hold power 480, 120 and low voltage conductors which are in cable tray rated conductors.

I think you might get more responses by starting a new thread, instead of posting a new question on an older thread.

But yes, IMO it still needs to be grounded. Somewhere in the code it will say what size wire you need to ground the trays (probably based on the largest circuit or feeder size ran in the tray).

Everything that is required to be grounded is basically connected back to the buildings grounding electrode system (the ground rods, water pipe, etc).

To me, what you are proposing would be similar to driving a separate ground rod somewhere and using that for grounding something instead of running a ground. Hopefully we all know that's generally not allowed.

 

[paulengr]

Read carefully. The tray can be an EGC or just a raceway. Grounding rules are different for each, You have to ground both but the non-EGC rules are more relaxed and it’s very easy to just pull a ground.

 

[tom baker]

I think you might get more responses by starting a new thread, instead of posting a new question on an older thread.

But yes, IMO it still needs to be grounded. Somewhere in the code it will say what size wire you need to ground the trays (probably based on the largest circuit or feeder size ran in the tray).

Everything that is required to be grounded is basically connected back to the buildings grounding electrode system (the ground rods, water pipe, etc).

To me, what you are proposing would be similar to driving a separate ground rod somewhere and using that for grounding something instead of running a ground. Hopefully we all know that's generally not allowed.

While you are asking about grounding, what we want is bonded or bonding…to create the low impedance path to open the OCPD in a line to tray fault. A ground path via strut will have high resistance and may not open the OCPD
And yes please start a new thread, to avoid confusing answers