Wiring question. Splicing DC wires.

[SunEagle]

Or you can do what a lot of electricians do in the field. They use split bolt connectors and a lot of 3M black electrical tap.

[sensij]

It's not so much a splice as transitioning from PV Wire from the panels to THHN in the conduit to inside. Which requires a pass-thru box, not wire nuts. I don't have my code book on me, but I thought PV wire was not supposed to go in conduit, thus the transition. I may be wrong, it could just be a cost thing, THHN is much less $ than PV Wire. Either way, don't use wire nuts in a moist location exposed to heat/cold. They will fail.

This. Check out Soladeck for an example.

[Sunking]

There's apparently at least 3 people who disagree with that:

http://forums.mikeholt.com/showthread.php?t=168428

But they're not using wirenuts either, which I would not do.

Tell me exactly where they say to use Wire Nuts for Transitions.

FWIW I am a Moderator on Mike Holt for the last 13 years, so I might know a thing or two about code.

[bcroe]

It's not so much a splice as transitioning from PV Wire from the panels to THHN in the conduit to inside. Which requires a pass-thru box, not wire nuts. I don't have my code book on me, but I thought PV wire was not supposed to go in conduit, thus the transition. I may be wrong, it could just be a cost thing, THHN is much less $ than PV Wire.

What is the issue with PV wire in conduit; metal or plastic? I know I have a couple dozen
wires in a cable management tray to keep things organized, leading to the combiner box
by the ground mount PV. Bruce Roe

[sensij]

What is the issue with PV wire in conduit; metal or plastic? I know I have a couple dozen
wires in a cable management tray to keep things organized, leading to the combiner box
by the ground mount PV. Bruce Roe

No problem with conduit. Cable tray was questionable, but NEC 2014 made this clearer. Snipped from this writeup:

Cable tray is a popular wire-management device for all sizes of systems, but the requirements in other sections of the Code about its use with smaller conductors, such as those used for PV source circuits, were confusing. Section 690.31(C)(2) now explicitly allows use of cable tray for PV-source and output circuits if they are listed PV wire, even when it’s not marked for use with cable tray. The enhanced durability of PV wire led to this allowance, along with the realization that, especially on commercial rooftop systems where thermal movement and expansion and contraction can wreak havoc, conduit may not always be the best installation method for conductors. The conductors in cable tray must be supported at least every 12 inches, and secured at least every 4.5 feet.

[Living Large]

Philosophically, I'd suggest it makes no sense to use wire nuts to connect the conductors of the DC power source to a house. If some resistance builds up, that puppy is going to fry.

Personally, it seems like this is one place to do the job right and not try save a few bucks.

[Amy@altE]

Thanks Sensji, I thought it had something to do with the insulation and heat build up. I might have been thinking about that. Thanks for the clarification.

[Sunking]

What is the issue with PV wire in conduit;

Nothing from a code perspective, it is a budget issue. The only technical difference between PV Listed Wire and THHN-2 is Voltage rating and UV, PV listed wire is rated for 1000 volts vs 600 for THHN-2. If you are in Europe that has an advantage but not here in the USA where voltage is limited to 600 volts. So it makes little sense for a contractor to pay twice as much for wire that has no usable advantage.

[foo1bar]

Tell me exactly where they say to use Wire Nuts for Transitions.

Post #1 in this thread abolev1984 said
"And using wire nuts for splicing..Big deal?"

And he/she has re-iterated the plan to use wirenuts since then too.

Or maybe you misread me - I said they (Mike Holt forum members) are NOT using wirenuts (and I wouldn't either).


It looks to me like pretty much all of them think doing a splice (from PVwire to THWN wire) is a good idea (or at least acceptable), while you asserted that "There is no good reason to have any splices. Would indicate a poor design and/or workmanship."

[sensij]

Nothing from a code perspective, it is a budget issue. The only technical difference between PV Listed Wire and THHN-2 is Voltage rating and UV, PV listed wire is rated for 1000 volts vs 600 for THHN-2. If you are in Europe that has an advantage but not here in the USA where voltage is limited to 600 volts. So it makes little sense for a contractor to pay twice as much for wire that has no usable advantage.

PV listed wire also has sunlight resistance, right? So it can be run without conduit (like USE-2), but THHN-2 can't. That's why it can make sense to do the rooftop with open PV wire, then transition to conduit with THWN-2 (or whatever is appropriate) and save some money on the rest of the home run.

[bcroe]

No problem with conduit. Cable tray was questionable, but NEC 2014 made this clearer. Snipped from this writeup:

" Cable tray is a popular wire-management device for all sizes of systems, but the requirements in other sections of the Code about its use with smaller conductors, such as those used for PV source circuits, were confusing. Section 690.31(C)(2) now explicitly allows use of cable tray for PV-source and output circuits if they are listed PV wire, even when it's not marked for use with cable tray. The enhanced durability of PV wire led to this allowance, along with the realization that, especially on commercial rooftop systems where thermal movement and expansion and contraction can wreak havoc, conduit may not always be the best installation method for conductors. The conductors in cable tray must be supported at least every 12 inches, and secured at least every 4.5 feet. "

Glad to hear that; I added 6' of cable tray to an unsupported run. Very little heat
there, but getting those 2 dozen wires into conduit would have meant dismantling
it all. Perhaps it doesn't meet the "secured at least every 4.5 feet" requirement
unless snapping on the lid counts. Could add a tie down in the center; gravity
is doing well right now. Bruce Roe

[Sunking]

It looks to me like pretty much all of them think doing a splice (from PVwire to THWN wire) is a good idea (or at least acceptable), while you asserted that "There is no good reason to have any splices. Would indicate a poor design and/or workmanship."

The keyword is SPLICE right? The definition of SPLICE is: To Weave or Twist together. That is what a wire nut does. The correct term is TRANSITION from one wire type to another which is done with either listed Term Blocks or Compression Taps. If an inspector opened up a J-box and found wire nuts used in wet or damp locations would fail the Inspection. IMO that constitutes poor design and/or workmanship likely to result in a failure and possible fire hazard.

[Sunking]

PV listed wire also has sunlight resistance, right?

Yeah that is why I said UV. I understand your point, but code still requires single cables to be in a protective raceway, secured, and protected from physical damage, and to keep the conductors closely coupled magnetically. You cannot lay conductors on asphalt shingles with staples. Eventually wind is going to move cables and the asphalt shingles will wear through the insulation not to mention a nice lunch for TREE RATS, and nesting material for birds. It would have to be some short of SHIELDED Armored Cable meaning more than one conductor in a protective jacket Armour, or CT rated cable in a rack system.

USE-2 is direct underground and does not require a raceway when under ground direct burial. When used above ground it is reclassified as RHW-2 which requires a protective raceway right?

[Sunking]

" Cable tray is a popular wire-management device for all sizes of systems, but the requirements in other sections of the Code about its use with smaller conductors, such as those used for PV source circuits, were confusing. Section 690.31(C)(2) now explicitly allows use of cable tray for PV-source and output circuits if they are listed PV wire, even when it's not marked for use with cable tray.

Don't hold your breath thinking that is going to hold up in latter code cycles. CT cable is more than 1 conductor in a common jacket. It is done so the conductors are closely magnetically coupled to minimize CHOKING which is critical for proper OCPD to operate.

[foo1bar]

The keyword is SPLICE right? The definition of SPLICE is: To Weave or Twist together.

That sounds like the definition of "braid", not splice.
Where are you getting that definition from? It's not from NEC.

The correct term is TRANSITION from one wire type to another which is done with either listed Term Blocks or Compression Taps.

I think the term splice covers that, as it is a more general term - it's any time you are joining the ends of two wires together, even if they are exactly the same size and type (while Transition I believe implies a change from one type to another)