Conduit size

Bluedog225 · Sep 17, 2023

I’d like to run some underground conduit from my conex to my cabin. It’s about 75 feet. And I want to run wire to accommodate split phase out of two Victron Quattros.

A couple of questions.

Question 1: Looking at the fill conduit fill tables to decide what size conduit I need to use. Do I count L1, L2, neutral, and ground each as a “conductor”? Therefore, 4 conductors? Or do I exclude the ground?

Question 2: I’m out in the country with no code or inspection. Is there any real-life safety issue with using schedule 40 pvc?

Thanks

pvgirl · Sep 17, 2023

All conductors in the conduit including the ground count to conduit fill, since they are all cables you are going to be pulling thru the conduit, and need to make sure fit.

Schedule 40 PVC conduit is allowed for underground and locations where not subject to damage. You may want to consider transitioning to schedule 80 for the above ground sections of the run.

BentleyJ · Sep 17, 2023

?

A clarification that doesn't apply to your situation specifically. If more than 3 conductors are in a conduit then the ampacity has to be derated. In this case the Ground wire(s) is not counted.

Balrog006 · Sep 17, 2023

BentleyJ said:
?

A clarification that doesn't apply to your situation specifically. If more than 3 conductors are in a conduit then the ampacity has to be derated. In this case the Ground wire(s) is not counted.

It is however considered when calculating conduit fill, southwire has great online calculators where you enter the type and size of conduit and type and size of all conductors and can effectively and properly size your conduit for your wire.

DVD · Sep 17, 2023

When you go above ground, best to transition to EMT or rigid. While you’re maybe not dealing with AHJs right now, it’s good to get the green light when it does come up.

DVD · Sep 17, 2023

Bluedog225 said:
I’d like to run some underground conduit from my conex to my cabin. It’s about 75 feet. And I want to run wire to accommodate split phase out of two Victron Quattros.

A couple of questions.

Question 1: Looking at the fill conduit fill tables to decide what size conduit I need to use. Do I count L1, L2, neutral, and ground each as a “conductor”? Therefore, 4 conductors? Or do I exclude the ground?

Question 2: I’m out in the country with no code or inspection. Is there any real-life safety issue with using schedule 40 pvc?

Thanks

So regarding sched 40, real safety issues?….. I’m not a big fan of building codes in general but I’ve come to understand their intent (beyond the insurance companies interests). While it’s more effort, bury it to the prescribed depths for the actual run. A trencher laying an irrigation line in the future……
Personally I try to avoid PVC above grade. Yes it’s sunlight resistant, but it can get a little brittle depending on exposure.

DVD · Sep 17, 2023

BTW: the Code Check series spiral bound books are a pretty good reference. Maybe in a local library?
Covers conduit fill run lengths etc. Includes some PV stuff but not in-depth

Bluedog225 · Sep 18, 2023

I appreciate the responses.

One more question. It looks like I can get 4 conductors (L1, L2, neutral, and ground) of 6 awg into 3/4 pvc conduit for the underground run. And if I switch to rigid metal conduit for the above ground portion, I can get 4 conductors in there as well.

My maths tell me that the Quattros will conservatively run 5000 watts at 120 volts so 42 amps each for LI and L2. Looks like that’s 6 awg copper for a 1.84% voltage drop at 50 feet.

A couple of follow-up questions:

1. Does anything in those calculations look obviously wrong?

2. What wire should I use? Is there any advantage or disadvantage in running direct burial cable in the conduit instead of THHN or THWN? Or is dual rated (thhn/twhn) the way to go? I don’t mind spending a little extra for long service life.

Thanks

drps10 · Sep 18, 2023

I know there is code and then there is what is best. Go bigger conduit! for a few extra dollars it will cost you to run the length you want, you'll thank yourself later when you have to actually pull 4 wires through, let alone #6 on top of that! And if you ever have to pull something extra, you'll have the room.

Bluedog225 · Sep 18, 2023

Makes sense. I’ve got a bunch of 2” schedule 80 laying around.

Though when go into my cabin, I’d like to scope it down to something smaller since I’ve got to drill through a 10” concrete wall (poor planning).

n2aws · Sep 18, 2023

drps10 said:
I know there is code and then there is what is best. Go bigger conduit! for a few extra dollars it will cost you to run the length you want, you'll thank yourself later when you have to actually pull 4 wires through, let alone #6 on top of that! And if you ever have to pull something extra, you'll have the room.

This.

I'd actually take this a step further. While you have the trench open and the initial manual effort is happening, bury a second conduit that will sit unused. If you never expand and use it, you're out a very small amount of money. if the day comes you DO want to use it, you'll have saved a boatload of time, effort, and money.

CoolWill · Sep 18, 2023

Save some money and effort and use #10 for the ground.

pvgirl · Sep 18, 2023

Bluedog225 said:
1. Does anything in those calculations look obviously wrong?

Sizing and voltage drop look good. You can also use a 10 awg conductor for the ground.

Bluedog225 said:
2. What wire should I use? Is there any advantage or disadvantage in running direct burial cable in the conduit instead of THHN or THWN? Or is dual rated (thhn/twhn) the way to go? I don’t mind spending a little extra for long service life.

For underground installations you need a wire rated for wet locations. THHN is only for dry locations, THWN is rated for wet locations and can be used underground. Multi rated conductors can also be used as long as they include a type that is approved for wet locations.

Bluedog225 · Sep 18, 2023

I’m curious why I get to use 10 awg for the ground. Couldn’t it possible carry the full load of both inverters? 10,000 watts.

And what would be a good candidate for leaving in the conduit to use for pulling wire in the future? Nylon strap?

pvgirl · Sep 18, 2023

NEC 250.122 Size of Equipment Grounding Conductors allows 10 awg ground up to 60 amps, the ground is not supposed to carry the full load for any period of time, usually just long enough for breakers to trip or fuses to blow.

A polyester pull tape would be best to leave in a conduit for future pulls, in an empty conduit. I would not count on being able to pull additional wires into a conduit with wires already it.

Bluedog225 · Sep 18, 2023

Thanks on the ground info. Makes sense.

On the conduit, I was hoping that if I go 2”, I’ve go so much extra space it would be ok. Tables say 22 conductors and I’ll have 4. Though I don’t know if a short would burn through the conductors and the pull tape.

n2aws · Sep 18, 2023

Bluedog225 said:
I’m curious why I get to use 10 awg for the ground. Couldn’t it possible carry the full load of both inverters? 10,000 watts.

And what would be a good candidate for leaving in the conduit to use for pulling wire in the future? Nylon strap?

I don't leave anything in the conduit. If I need to pull something later, I get a plastic shopping back (the kind you get at the grocery store), a kite string and a wet/dry vac.

suck the bag through the conduit with the vacuum. then tie the kite string to whatever muletape you are using to pull with, and pull it through.

SparkyJJO · Sep 18, 2023

n2aws said:
I don't leave anything in the conduit. If I need to pull something later, I get a plastic shopping back (the kind you get at the grocery store), a kite string and a wet/dry vac.

suck the bag through the conduit with the vacuum. then tie the kite string to whatever muletape you are using to pull with, and pull it through.

That's brilliant.

n2aws · Sep 18, 2023

SparkyJJO said:
That's brilliant.

I'd love to take credit for it, but it's something my dad showed me like 30 years ago. No idea where he learned it.
But, I've seen the same process used all over the place, so it's decently well known, I'd imagine

rhino · Sep 18, 2023

xhhw-2 will have thicker insulation and more flexible if you wanted the "best" cable to use. Slightly more expensive. Also if you want to make it easier when pulling make sure to use a lubricant. You'd be surprised how much friction can be generated by a bunch of cables rubbing against conduit.

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