Condiut Fill

newenergy

I have an installation coming up (probably, I hope) on a detached garage and there is an existing conduit route through a concrete wall and under the driveway. The conduit is 1/2" PVC. I think it's Sched. 40.

They put the conduit in there for an outlet for xmas lights and a couple lights in the garage.

Table C.10 in Annex C in the NEC (2005-8 at least) are telling me that I can put up to 5 10 AWG THWN in there. That conductor would serve my needs after all derations, including conduit fill.

Am I missing something? 1/2" PVC seems too small for this.

crewzer

Re: Condiut Fill

I agree that Table C.10 for Schedule 40 conduit indicates it’s OK to run five #10 conductors of THWN-2 wire through "½ inch" conduit (closer to 0.63 inches, I think). However, it’s probably worth reviewing all of the applicable deratings.

1) Determine conductor (insulation) temperature rating.
2) Use Table 310.16 (“…three conductors in a raceway…”) to determine ampacity at 30 C ambient. Do not use Table 310.17 ("free air").
3) Use Table 310.16 again (lower 1/3 of Table) to apply ampacity correction factor for ambient temperature other than 30 C.
4) Use Table 310.15(B)(2)(a) to determine adjustment factor for >3 current-carrying conductors in conduit. For example, adjustment factor for 5 conductors is 80%.

HTH,
Jim / crewzer

GreenerPower

Re: Condiut Fill

Take a look at this site - http://www.thespreadsheettool.com/free_stuff.htm
Some helpfull spreadsheets. Run virus-scan on the exe though. I've used it once a long time ago, seems reasonable.
GP

newenergy

Re: Condiut Fill

thx, I think I've got the derations covered and maybe overdone.

Short Circuit x 1.56 (690.8) x 1.25 (conduit fill 310.15) / .58 (temperature deration on roof)

The Short Circuit current is 8.13 amps, so the total gives me 27.33 amps and #10 is rated for 35 amps in 310.16. I will be trying to get THWN-2 but it's hard to find and no one seems to care, but as I understand you have to use the 75 degree rating anyway because the terminals are only ever rated for 75 degrees.

The over deration could be because of the temperature factor. For one thing it's near the beach and it's really not that hot here, but reading John Wiles and other sources have just led me to making this temperature deration. I've asked non-solar electricians though and they didn't seem to use those derations unless they were running wire through hot equipment or something.

At any rate the inverter requires a minimum of #10 for all DC wiring connections, so I couldn't go any smaller. Theoretically I guess I could go with #10 on the roof, splice to smaller wire for the underground conduit run, and then splice back to #10 for the inverter, but that seems pretty wrong.

One more thing about wire, supposedly 90 degree wire is considered the best practice, but I know people (at big companies) who never use it. I guess I should use it, but it is hard to find. I saw a previous thread on here about this and see they carry the tray cable here, but not individual wire.

newenergy

Re: Condiut Fill

Ok, sometimes things are actually easier to find the old fashioned way. I looked on the inet for a long time, but just called around and the 3rd electrical supply store had #10 THWN-2. It's $110 for 500', which is about $20 more than #10 THWN at home depot, so not too big a deal.

newenergy

Re: Condiut Fill

Ok, thanks for the help, but this seems to be moot. 690.4(B) says you can't mix PV circuit with other circuits in the same conduit.

JDR*energy

Re: Condiut Fill

Is this really true about 690.4(B)? I am planning the same project with detached garage with existing conduit. (2" I think). I have 2 hots and a neutral for 220v service to my garage. I was going to run 8 or 10 AWG through it for my PV.

Ugh.. Since this is an "off-grid" system I thought I would be able to get away with a little more flexibility when it comes to code issues.

Solar Guppy

Re: Condiut Fill

Saftey has nothing to do with on or off grid.

The Code is there to prevent bad things ... mixing AC with any other system is very bad, what happens if water got into the conduit, it could have the DC or low voltage runs conducting AC for example

One need seperate conduit for AC / DC / Low voltage no mixing allowed.