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smitty286 04-07-2008 02:33 PM

Conduit Spacing / Separation
Does the NEC specify a minimum distance between buried conduits, or any additional derating that needs to be done due to close proximity? I’m planning to run 3 PVC conduits between my house and the garage in the same trench and at the same depth. Figure 310.60 in the 2008 NEC shows a spacing of 7.5” between conduits in such a duct bank, but I couldn’t find any reference to spacing in the code (my guess is that this simply means that conduits more than 7.5” apart are no longer considered to be part of the same bank). I’d like my conduits to be much closer together for aesthetics, such that the LBs at the building entry points only have maybe 1/2” or so between them, but I want to make sure I’m not missing any derating concerns with this setup (all wiring is copper):

Conduit #1: 1” PVC containing three #6 THWN feeder wires and one #10 EGC. Ampacity calculated at 65A, breakered at 70A using “next standard size” rule. Will rarely if ever see that level of loading (sized to accommodate a large arc welder with a little to spare for lighting, but will not see more than 10-15A).

Conduit #2: ¾” PVC containing three #12 THWN wires and one #14 EGC from a three-way light switch inside the house (could have been included in conduit #1, but I would have then had to breaker the feeder at 60A due to additional required derating). Circuit is part of a lighting branch protected by 15A breaker, actual max load of about 3A on these wires.

Conduit #3: ¾” PVC containing two CAT5e phone/data lines.

nap 04-07-2008 05:32 PM

throw them in the hole and bury them but you need to change that #14 EGC to a #12.

and you need to upsize the #10 EGC to a #8.

220/221 04-07-2008 05:33 PM

No spacing required.

Throw em in and kick the dirt back in.

smitty286 04-08-2008 10:11 AM

Thanks for responding, guys, and thanks for that catch nap....I originally planned to put the #6's and #12's in the same pipe, making it a 60A feeder with a #10 EGC...forgot to upsize when I moved the 12's to their own conduit (the #14 in that pipe was a typo).

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