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Discussion Starter · #1 ·
Hey everybody, I am running 52 x 120v 20a circuits with SO cable drops throughout a warehouse. I have 165' of wire trough, piping out every 20' to 2 4S boxes on each side of the trough. I have a neutral for each box, and 2 circuits per box. I'm trying to figure out the minimum number of ground wires to pull through the trough from the 120/208v 3-phase panel while still being up to code. Any ideas? An NEC book section would be awesome too!

Thanks!


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I own stock in FotoMat!
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NEC will allow one? Any chance you can cite the section of the code book?

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Nothing to cite. NEC is a permissive document. If it doesn't say otherwise, it would be legal. Since there's no requirement to install a separate ground for each individual circuit, one is all that's required.
 

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It says in the nec you can run just 1 look under 250.122 (c) Multiple Circuits. Where a single equipment grounding conductor is run with multiple circuits in the same raceway,cable,or cable tray, it shall be sized for the largest over current device protecting the conductors in the raceway,cable,or cable tray.

Then if you see 250.122(1) it references you to the chart for wire size.

Max circuit breaker feeding your raceway is 20a you run 1-#12 for all 52 of your circuits just set some ground bars every couple feet in your trough and jump them out to carry the bond down the length of your trough and bring all your grounds to them.
 

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Don't forget this little gem:

376.22 Number of Conductors and Ampacity. The number of conductors and their ampacity shall comply with 376.22(A) and (B).

(A) Cross-Sectional Areas of Wireway. The sum of the cross-sectional areas of all contained conductors at any cross section of a wireway shall not exceed 20 percent of the interior cross-sectional area of the wireway.

(B) Adjustment Factors. The adjustment factors in 310.15(B)(3)(a) shall be applied only where the number of current-carrying conductors, including neutral conductors classified as current-carrying under the provisions of 310.15(B)(5), exceeds 30. Conductors for signaling circuits or controller conductors between a motor and its starter and used only for starting duty shall not be considered as current-carrying conductors.

Pete
 
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Discussion Starter · #12 ·
So does the NEC define EMT and the wire trough the same way? If I split the conductors up, will I need to derate the same once they come together in the trough as if they were all in the same pipe?


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CRStarbird said:
So does the NEC define EMT and the wire trough the same way? If I split the conductors up, will I need to derate the same once they come together in the trough as if they were all in the same pipe? Sent from my iPad using Tapatalk
No. It applies to circular raceways. The article for metal wire ways was posted above, but it would still apply in your case because your over 30 CCC's
 

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CRStarbird said:
So does the NEC define EMT and the wire trough the same way? If I split the conductors up, will I need to derate the same once they come together in the trough as if they were all in the same pipe? Sent from my iPad using Tapatalk

Look in the code book and find out.
310.15(b)(3)(a) adjustment factors for more than three current carrying conductors.
Table 4 conduit or tubing fill
366.22 (a) and (b) tells you how to calculate the trough size
366.23(a) and (b) tells you how to derate the amps of your wires, 30 or less 310.15(b)(3)(a) don't apply but it does apply to the pipe you fed it with and what you get when you derate for that applies for the whole run.
 
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