NM Cable Entering Enclosure

[timm333]

A question about NEC rule 312.5-C. An exception below this rule states that nonmetallic sheath cables are permitted to enter from the top of enclosure through non-flexible raceway. Can a cable tray be used here as non-flexible raceway? For example if we use 18 inch cable tray entering the enclosure from top, and tie the cables to the cable tray, would it be acceptable?

 

[Coppersmith]

No, that raceway has to be a pipe or trough as evidenced by:


...provided all of the following conditions are met:

(c) A fitting is provided on each end of the raceway to
protect the cable(s) from abrasion and the fittings remain
accessible after installation.


(d) The raceway is sealed or plugged at the outer end
using approved means so as to prevent access to the enclosure
through the raceway.

Try doing either of those with a cable tray.

Now if the NM was run in cable tray and then entered an 18" pipe going into the enclosure and was properly fastened, that would be OK.

 

[Buck Parrish]

I too, was wondering how you were going to attach the cable tray to the enclosure. It seems you would have to have some nipples.

 

[timm333]

Thanks. A couple of questions:

The exception below NEC 312.5-C has 7 conditions ( a through g). Condition (a) requires that each cable is fastened within 12 in of outer edge of raceway. Does “outer” end here mean each of the two ends of the raceway?

Condition (c) requires a fitting on each end of the raceway, what kind of fitting can be used for trough type tray?

 

[Coppersmith]

Thanks. A couple of questions:

The exception below NEC 312.5-C has 7 conditions ( a through g). Condition (a) requires that each cable is fastened within 12 in of outer edge of raceway. Does “outer” end here mean each of the two ends of the raceway?

No, just the top side. The other end is inside the enclosure and doesn't require fastening.

Condition (c) requires a fitting on each end of the raceway, what kind of fitting can be used for trough type tray?

I'm not sure. I've always done this with pipe. I would guess a chase nipple installed in the end cap would be acceptable.

 

[timm333]

Thanks. So if NM is run in ladder-tray and then entered an 18" pipe going into the enclosure, how to fasten the cable within 12 in of outer edge of raceway?

Also should the pipe be connected to the tray by lock-nuts; or will it be Ok to keep the pipe 6 inches away from the tray, and a bonding jumper sized as per 250.122 is used to connect the pipe and tray for electrical continuity?

 

[augie47]

In looking at 392.10(A) and 334..10(4) would the NM not have to be identified for use in Cable Tray.
(Just curious as Ive not seen NM in Cable Tray on NM identified for use in Cable Tray)

 

[timm333]

Also will it be Ok that the cables for the main-breaker are entered into the cabinet from the bottom using cable-connectors, and the cables for the outgoing feeders are entered into the cabinet from the top using non-flexible pipes?

 

[timm333]

In looking at 392.10(A) and 334..10(4) would the NM not have to be identified for use in Cable Tray.
(Just curious as Ive not seen NM in Cable Tray on NM identified for use in Cable Tray)

Actually NM is allowed in cable tray as it is listed in Table 392.10(A)

 

[augie47]

Actually NM is allowed in cable tray as it is listed in Table 392.10(A)

I understand that but it also refers you back to the wiring method Article and 334.10(4) requires the NM be identified for the use in cable trays.

 

[Coppersmith]

how to fasten the cable within 12 in of outer edge of raceway?

The cables can be individually zip-tied to a rung before entering the pipe.

Also should the pipe be connected to the tray by lock-nuts; or will it be Ok to keep the pipe 6 inches away from the tray, and a bonding jumper sized as per 250.122 is used to connect the pipe and tray for electrical continuity?

The pipe does not have to be connected to the tray. It's acting as a sleeve, not a complete raceway. As long as the pipe is fastened near the top as required. I'm not sure of the bonding requirements, but certainly if you bond the tray to the pipe you will be compliant. A grounding bushing on the end of the pipe would fulfill both the fitting and bonding requirements. The pipe is not required to be metal however. It could be PVC if that is allowed in your environment.

 

[timm333]

Is 312.5 also applicable to DC systems ?