NM/UF - Conduit - Roof?

[where2]

Here's a question I cannot seem to find the answer to:

I'd like to make the following 240V AC run using NM-B or UF-B (10/3+gnd) for as much of the run as possible. I need to get from a combiner panel on the outside of the house with a 20A OCPD, up a PVC conduit to a knee wall attic (non-storage), up through the second floor wood frame exterior wall, up into the non-storage attic (ladder required, not pull down), then out the roof in conduit to a junction box to mate to the solar system USE-2 wire. I also need to get a #6 EGC from the roof to the combiner panel.

Do I need to use THWN for the roof conduit segment?
Do I need to use THWN for the exterior wall conduit segment?
The load is 9A, the house is in South Florida (humid and 40°C in the shade in the middle of summer), I actually need two parallel runs @9A.

I considred making the run THWN in 1" conduit for the entire run, but making the bend from the wall to the 2nd floor attic is going to be a challenge with only 2x4 trusses making the radius tight using 1" PVC. Working a wire in a PVC LB there would be a nightmare!

Is there a max allowable length of NM-B or UF-B inside a conduit before derating is necessary? 24"? I know customarily you avoid running these jacketed cables in conduit, but I need the conduit for protection between the attic and the combiner panel and the attic to the roof mount J-box.

Lastly, when run inside the structure (or conduit) should the #6 EGC be insulated?

According to the ENT conduit fill tables, a 3/4" conduit reaches capacity at seven 10 AWG THWN conductors, I need 8 plus that pesky #6 EGC. So, it appears 3/4" ENT is out of the question.

 

[pattenp]

The 10/3 can be UF the whole run. There is no restrictions on the length that can be in conduit. Also size the conduit based on the widest dimension of the UF as if a single conductor. The #6 EGC can be bare.

Edit: If this circuit is protected by a 20A breaker then the wire only needs to be #12.


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[Norcal]

The 10/3 can be UF the whole run. There is no restrictions on the length that can be in conduit. Also size the conduit based on the widest dimension of the UF as if a single conductor. The #6 EGC can be bare.

Edit: If this circuit is protected by a 20A breaker then the wire only needs to be #12.


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Incorrect, see 250.122(B) 2011 NEC

(B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors.

There are no exceptions to this rule.

 

[walrus]

Doesn't solar wiring from the panel to inverter need to be in rigid conduit? or is this one of those systems with the inverter built into the panel

 

[pattenp]

Incorrect, see 250.122(B) 2011 NEC

(B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors.

There are no exceptions to this rule.

You lost me on the citing of 250.122(B). I'm saying the 10/3 only needs to be 12/3 if the OCPD is 20A. Are you thinking I'm saying to reduce the #6 EGC to a #12? I think the #6 is actually an earth ground and not an equipment ground. Either way, where are you coming from on this?

 

[where2]

Doesn't solar wiring from the panel to inverter need to be in rigid conduit? or is this one of those systems with the inverter built into the panel

This is 240V AC, with the micro-inverters on the roof, not a DC series array with over 65VDC. I can understand why you want series DC circuits in conduit, but thats a different game... One of the main intents in keeping the DC wiring contained in conduit is to avoid cutting it while venting an attic in the event of a fire while the sun is up. PV panels in sunshine produce power with or without a fire in the house. With micro-inverters, you have 36v, 6A at each (220W) panel in full sun.

The #6 GEC (grounding electrode conductor) is a ground reference for the DC leads of the PV module. (I mistakenly labeled it GEC when I originally wrote this, and SBerry commented on this error later in this thread). I will not be down-sizing the #6AWG, although a separate set of lightning rods on the roof peak and a OOO to an array of ground rods might not be a bad idea in this lightning capital of the world.

 

[where2]

With two pieces of 10/3 UF-B, having a sectional area of 727x215 (mils), and one piece of 6AWG bare with a diameter of 162 mils, it appears I need a 2" conduit to stay under 40% fill. Funny, the feeder to the house is only in 2" conduit!

 

[hh76]

Keep in mind that there are additional derating factors when running conduit on a roof surface. I don't have my book in front of me, but it is a simple chart that refers to the height of the conduit above the surface.

 

[where2]

Keep in mind that there are additional derating factors when running conduit on a roof surface. I don't have my book in front of me, but it is a simple chart that refers to the height of the conduit above the surface.

I concur, but at a 23% fill using a 2" conduit and +1 over size on my wiring, the derating for roof conduit doesn't hurt me too much. That was one of the reasons I had 10AWG wire for my 9A circuit.

Is a weather head considered roof conduit? I've been debating just bringing the USE-2 down a weather head and splicing to #10 UF-B in the attic.

 

[pattenp]

The USE-2 and UF-B splice needs to be made outside of the structure. USE-2 is not approved by the NEC to be brought inside of the structure. I don't think it's a big deal, but figured you should know.

 

[sberry]

The #6 EGC is earth ground to provide ground fault protection if something should short

No it isnt.

 

[pattenp]

No it isnt.

Come on sberry... you can give the guy more input than that!

 

[where2]

The USE-2 and UF-B splice needs to be made outside of the structure. USE-2 is not approved by the NEC to be brought inside of the structure. I don't think it's a big deal, but figured you should know.

Thanks PattenP, I just checked the jacket on the wire in question, it's NOT USE-2, it's TC-ER THHN/THWN-2 and labeled sunlight resistant, oil res II dir bur or UL CIC/TC PVC/N.