vertical conduit and wire - cable stress relief

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mshields

mshields

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Boston, MA
An EC on a job we designed has run a 6 story vertical feeder with a pull boxes (not sure if one or 2) which I know is in keeping with what's required for stress relief on the cables. The owner wants him to put in cat walks to make the pullboxes accessible (I suppose that would make them readily accessible and that therein may lay the crux of this). I don't believe this is required. Does anyone have a different take and if so based on what?

Thanks,

Mike
 
You need cable supports every X feet based on the size and type of conductor. The boxes only need to be accessible.
 
infinity said:
You need cable supports every X feet based on the size and type of conductor. The boxes only need to be accessible.
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One thing I've wondered about how the requirements for this issue are supposed to work. Suppose a given conductor's support interval as specified in the NEC is X vertical feet. Consider the following cases:

A: the vertical run is exactly X vertical feet.
B: the vertical run is X+1 vertical feet
C: the vertical run is X-1 vertical feet

Does this mean that A would require 1 support, B would require 2 supports, and C would not require any supports, assuming the top support is at the very top of the run?

Alternatively, could you intentionally support conductor in case B, at a location 2 feet below the top of the run, as a clever way to get around a need to use 2 supports? The article doesn't really quantify what "as close to the top as practical" means. It's clear that supporting (2*X-1) vertical feet of conductor could not be done with just one support at the midpoint, but I could see cases that are slightly taller than X vertical feet, where someone would try to make it work with just one support location.
 

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i eat my hat, kellems grip type cable support for riser applications in that catalog. Neat!
 

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Carultch said:
One thing I've wondered about how the requirements for this issue are supposed to work. Suppose a given conductor's support interval as specified in the NEC is X vertical feet. Consider the following cases:

A: the vertical run is exactly X vertical feet.
B: the vertical run is X+1 vertical feet
C: the vertical run is X-1 vertical feet

Does this mean that A would require 1 support, B would require 2 supports, and C would not require any supports, assuming the top support is at the very top of the run?
Click to expand...
From the 2017 NEC:

300.19(A) Spacing Intervals — Maximum. Conductors in vertical raceways shall be supported if the vertical rise exceeds the values in Table 300.19(A). At least one support method shall be provided for each conductor at the top of the vertical raceway or as close to the top as practical. Intermediate supports shall be provided as necessary to limit supported conductor lengths to not greater than those values specified in Table 300.19(A).

So case A would not require any supports. Case B would require 1 or 2 supports, depending on whether the highest practical support leaves more than X feet below it unsupported.

Cheers, Wayne
 
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