To Transition or not to Transition, PV wire to THHN

[Quattrohead]

I have grown to like wire nuts and that's coming from a foreign country. At first I thought they were bizarre things.
AC/DC don't know what the difference could be.

 

[zanydroid]

Each string is producing about 14 amps, so I should be okay. Am I missing something

There is a 1.56 derating multiplier on top of Isc@STC. Roof is damn hot

And both temperature and conduit fill derate stack, is that factored into your .7?

 

[Skypower]

What you can do it run PV wire into a box, either NEMA 4 and install a junction block or you can use something like a PV disconnect such as the IMO. Mount the IMO outside of the structure, then run metal conduit into the structure. This allows you to not only transition the wire but also the conduit.

The other choice is a box like the Vevor I used. You mount a DIN rail inside with a breaker and SPD's. You make the transitions there, mount it outside the structure and transition to metal conduit into the structure.

View attachment 194584

I like those things in a metal box outside just like you have that. I have the same ones. Do tighten the terminals. They loosen with time and they get gooey and burnt if you don’t. Like a marshmallow

 

[garybryan33]

There is a 1.56 derating multiplier on top of Isc@STC. Roof is damn hot

And both temperature and conduit fill derate stack, is that factored into your .7?

Okay, now I am in over my head. No, I did not consider this, and I am not sure how to factor that in. Here is my best shot

Isc=Is×Derating Factor

Assuming Is is 14 amps:

Isc=14 A×1.56Isc=14A×1.56

Isc=21.84 

Assuming this is correct, and now I am .84 out of spec, what are my options? Run multiple conduits?

 

[zanydroid]

Assuming this is correct, and now I am .84 out of spec, what are my options? Run multiple conduits?

Installers tend to just bend EMT on the roof. In that case you can start derating from the 90C rating of the conductors. Though note hard PVC has 80C rating so if that is used for part of the run some adjustments would have to be made on the starting point of derate.

Another possibility is to use limited amounts of LFMC and see if you can get away with 10ft / 10% rule.

 

[garybryan33]

Installers tend to just bend EMT on the roof. In that case you can start derating from the 90C rating of the conductors. Though note hard PVC has 80C rating so if that is used for part of the run some adjustments would have to be made on the starting point of derate.

Another possibility is to use limited amounts of LFMC and see if you can get away with 10ft / 10% rule.

Okay, I think I will process all this information as I sleep. One last thing, in your initial comment you mention a condition, "when wet." I am not sure how that fits, can you elaborate? Here, wet weather happens in cool months, and roof temps are not hot. It's fair to say that I have not taken temperature samples though.

 

[zanydroid]

Okay, I think I will process all this information as I sleep. One last thing, in your initial comment you mention a condition, "when wet." I am not sure how that fits, can you elaborate? Here, wet weather happens in cool months, and roof temps are not hot. It's fair to say that I have not taken temperature samples though.

When the plastic gets wet.

You can maybe negotiate with your AHJ about that.

Still sounds like a hack job vs just spending 3 hours bending EMT like a DIY caveman until you accidentally get it right.

 

[Zwy]

MC Run on the roof though???

Don't know where that came from, the discussion was about metal conduit inside a building.

 

[Skypower]

When the plastic gets wet.

You can maybe negotiate with your AHJ about that.

Still sounds like a hack job vs just spending 3 hours bending EMT like a DIY caveman until you accidentally get it right.

Lol, watching an experienced commercial electrician bending conduit is like watching an artist. Just don’t talk to him and watch too closely or he’ll charge you extra lol!

 

[zanydroid]

Don't know where that came from, the discussion was about metal conduit inside a building.

There was a post from the OP saying they wanted to use MC on the roof, and it was affirmed in a followup from someone which I thought was super surprising, I suspect someone mis read missing either MC or wanting to use it on roof.

Post #17 from OP

And Post #18 from you replied saying it was OK

 

[garybryan33]

There was a post from the OP saying they wanted to use MC on the roof, and it was affirmed in a followup from someone which I thought was super surprising, I suspect someone mis read missing either MC or wanting to use it on roof.

Post #17 from OP

And Post #18 from you replied saying it was OK

At that point, we were discussing liquidtight Flxible MC. The run from the roof to where it goes into the structure is 10ft. Four feet on the roof and about another 4 feet down the wall.

 

[zanydroid]

Ok when I read MC I don’t assume LFMC. Retracted

If you want to use LFMC and avoid derating concern go to #8 or #6 conductors