Why can't you transition from PV Wire to THWN-2 via MC4 connectors?

[HX_Guy]

Or can you? I'm guessing it's not to code, but having a hard time understanding why.

For example if you use PV Wire to link all the panels together in series but then need to run through conduit to the combiner box, the usual way seems to feed the PV Wire into a junction box and splice it with THWN-2 in the box. If MC4 connectors are ok for interlinking modules, why is it not ok as a splice?

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To clarify, say you have a small group of panels on one portion of the roof, and the next group of panels is say 20' away...I've seen where the module wires enter into conduit and the back out 20' later to connect to the next panel. Is that not proper?

Something like this:

[foo1bar]

To clarify, say you have a small group of panels on one portion of the roof, and the next group of panels is say 20' away...I've seen where the module wires enter into conduit and the back out 20' later to connect to the next panel. Is that not proper?

Something like this:

If there were no additional connections being made - it's just a straight run as shown in the picture- then I'd probably run PVWire inside the conduit. (AFAIK it's perfectly fine to run PV wire within a conduit provided you're meeting fill requirements and the wire is protected from edge of the conduit (ie. not possible for the wire to rub on the end of the conduit)


As for MC4 connector with THWN-2 - are they listed for use with THWN-2? (probably not - but I'll leave it to you to look up.)
Will the connector provide a water-tight seal? (probably not - I think insulation is smaller diameter on THHN/THWN. Which is why I am guessing they're not listed for that use.)

Are you thinking of having the THWN-2 be outside of conduit and J-boxes? That would be a problem code-wise.

[HX_Guy]

I think the problem is that PV Wire is too thick to run inside conduit, or at least that's what I've read. I need 6 wires and a bare ground and it'll be 1" EMT.

Ok so THWN may not work, but what about USE-2?

Probably best to just go with a J Box and not complicate things.

[foo1bar]

I think the problem is that PV Wire is too thick to run inside conduit, or at least that's what I've read. I need 6 wires and a bare ground and it'll be 1" EMT.

Ok so THWN may not work, but what about USE-2?

Probably best to just go with a J Box and not complicate things.

I'm not sure where you're getting "too thick to run inside conduit".
I just recently pulled wire that was ~1" diameter through conduit (although that was through much bigger than 1" EMT)

Look up what diameter the wire is, figure out the conduit fill and make sure you're good there.
Then make sure you're taking into account any current-capacity derating because of temp - since it's conduit on top of the roof.

[inetdog]

I think the problem is that PV Wire is too thick to run inside conduit, or at least that's what I've read. I need 6 wires and a bare ground and it'll be 1" EMT.

Ok so THWN may not work, but what about USE-2?

Probably best to just go with a J Box and not complicate things.

Each model of MC4 connector will specify the diameter or wire type and size with which is can be used. If you find an MC4 connector that will work with your PV wire, and possibly a different model that will work with your THWN or USE-2, then you can mate them together, since the connector portion is standardized.
Another problem with electrical code is that in general (not for in array connections to panels or combiners) it is permissible to leave MC4 connectors in the open. But for the connection to normal house wiring in conduit you may find that you need to make the transition inside a weatherproof box (which you may need on the end of the conduit for a seal anyway!)

[SunEagle]

Or can you? I'm guessing it's not to code, but having a hard time understanding why.

For example if you use PV Wire to link all the panels together in series but then need to run through conduit to the combiner box, the usual way seems to feed the PV Wire into a junction box and splice it with THWN-2 in the box. If MC4 connectors are ok for interlinking modules, why is it not ok as a splice?

--------

To clarify, say you have a small group of panels on one portion of the roof, and the next group of panels is say 20' away...I've seen where the module wires enter into conduit and the back out 20' later to connect to the next panel. Is that not proper?

Something like this:

Out of curiosity, what do the permitted installation drawings show for the wire and conduit size for these runs?

Also are you sure you need THWN - 2 wire because a #2 gauge wire with THWN insulation is good for about 115 amps. Do you mean to say is it a 2 conductor THWN #8 or #10 gauge wire or something in the 50 to 30 amp wire size range?

[HX_Guy]

For the array to combiner box wiring, the permit shows #10 USE-2 in 1" EMT (where applicable). Apparently my installer didn't have any plans to put it in any conduit though, he was just going to leave it loose.

The -2 in the THWN means that the wire is rated for 90º C, vs regular THWN wire that's rated for 75º C, at least according to this DIY guide: http://www.thesolarplanner.com/steps_page9.html

[SunEagle]

For the array to combiner box wiring, the permit shows #10 USE-2 in 1" EMT (where applicable). Apparently my installer didn't have any plans to put it in any conduit though, he was just going to leave it loose.

The -2 in the THWN means that the wire is rated for 90º C, vs regular THWN wire that's rated for 75º C, at least according to this DIY guide: http://www.thesolarplanner.com/steps_page9.html

Sorry I missed that. You are correct the THWN - 2 is 90º C rated wire for wet applications.

While USE -2 wire can be run without conduit, leaving it exposed on the roof for a 20' run would be wrong.

Since there isn't any Conduit Fill table for USE cable, based on the wire OD you could use that 1" EMT and run a few through it but I am not sure if it will pass even two #10 wires with an MC-4 connector.

Was the plan to run the USE-2 in EMT and then add the MC-4 connectors?

[HX_Guy]

Was the plan to run the USE-2 in EMT and then add the MC-4 connectors?

Correct, I was thinking the wire could be run through and then use an MC4 connector tool to add on the connector after the wire is through.
I've seen people say the tool is $200+ but Amazon has them for $25 - $45?

http://www.amazon.com/Signstek-Crimping-Crimper-2-5-6mm2-Connector/dp/B00FWNVW0W

[SunEagle]

Correct, I was thinking the wire could be run through and then use an MC4 connector tool to add on the connector after the wire is through.
I've seen people say the tool is $200+ but Amazon has them for $25 - $45?

http://www.amazon.com/Signstek-Crimp.../dp/B00FWNVW0W

I would say that based on what inetdog said about matching up your wire OD size to the correct MC-4 connector it could be done.

You may want to look into an EMT fitting that has a compression ring on each end. That will help prevent the insulation from rubbing against the edge of the EMT conduit.

The only issue I see is if you have a problem with one of those USE-2 wires you may have to remove all of the MC-4 connectors to pull out the bad wire and replace it with a new one. But there is a pretty low possibility of requiring that if you are careful when you pull the wire through and protect the insulation from getting scraped.

[HX_Guy]

Hopefully my luck isn't THAT bad that the wire would get damaged when pulling it through.

So it sounds like it could be done, with USE-2 wire, with MC4 connectors, and a junction box wouldn't be needed?

And I'm still trying to understand why THWN-2 couldn't be used instead of USE-2 if it's through conduit? While a very small part would be exposed outside of conduit (part that comes out of conduit and has an MC4 connector on it), it would be under the solar panels and not exposed to direct sunlight which I understand is the only difference between USE-2 and THWN-2 (USE-2 is sunlight resistant while THWN-2 isn't).

[SunEagle]

Hopefully my luck isn't THAT bad that the wire would get damaged when pulling it through.

So it sounds like it could be done, with USE-2 wire, with MC4 connectors, and a junction box wouldn't be needed?

And I'm still trying to understand why THWN-2 couldn't be used instead of USE-2 if it's through conduit? While a very small part would be exposed outside of conduit (part that comes out of conduit and has an MC4 connector on it), it would be under the solar panels and not exposed to direct sunlight which I understand is the only difference between USE-2 and THWN-2 (USE-2 is sunlight resistant while THWN-2 isn't).

Correct THWN is not sunlight resistant. What is strange is that "USE" is really designated as Underground Service Entrance rated wire so really shouldn't see the light of day.

When the NEC Article 690 for PV installations was added they referenced using the single conductor USE-2 cable but it must be labeled "PV" which is permitted to be used in exposed outdoor locations in and around the solar array.

[foo1bar]

Correct, I was thinking the wire could be run through and then use an MC4 connector tool to add on the connector after the wire is through.
I've seen people say the tool is $200+ but Amazon has them for $25 - $45?

http://www.amazon.com/Signstek-Crimp.../dp/B00FWNVW0W

I'd have to do more research before I'd go that route.

I have budgetted $300 for a Rennsteig crimping pliers with locator, and that's currently my plan.

$300 seems a bit high to me, but $45 might be a little low.
$25 is definitely too low - I think those are non-parallel jaw type that I definitely wouldn't use.

[foo1bar]

Hopefully my luck isn't THAT bad that the wire would get damaged when pulling it through.

It doesn't take much to damage the insulation when pulling it through. (been there, done that)

But the thing I would be more concerned about is any metal edge that could slowly abrade the wire insulation as it moves in the wind.

[HX_Guy]

I'd have to do more research before I'd go that route.

I have budgetted $300 for a Rennsteig crimping pliers with locator, and that's currently my plan.

$300 seems a bit high to me, but $45 might be a little low.
$25 is definitely too low - I think those are non-parallel jaw type that I definitely wouldn't use.

I don't know, it has 5/5 stars with 13 reviews so seems ok. Maybe it's not great for long term use but for a few crimps?