PV Wire vs USE-2 for a PV installation
- Thread starter Pitt123
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- Massachusetts
What is 'PV wire'?
If it is not also listed by a name found in Table 310.13 you cannot use it at all for NEC applications.
If it is not also listed by a name found in Table 310.13 you cannot use it at all for NEC applications.
I have heard the term "PV Wire" used when discussing the differences between USE-2 wire and PV wire for module interconnections in PV systems. The following is an excerpt from a wire manufacturer explaining the benefits of using PV wire over USE-2. I'm not sure if this is true or just the manufacturer marketing its PV wire:
"In the past, USE-2 copper wire has been used in PV applications; the emergence of the PV wire standards has replaced it as the choice for solar module interconnections. PV is superior for multiple reasons over its predecessor USE-2.
First, PV wire can be rated at 600V, 1KV or 2KV voltage levels. Next, PV wire can be used in both grounded and ungrounded PV arrays. Also, PV wire has a thicker insulation/jacket giving it more abrasion and mechanical protection. PV wire can be found in 16 AWG and 18 AWG while USE-2 smallest available size is 14 AWG. Finally, and most important, PV wire must comply with most stringent sunlight (UV) resistance and be flexible at the extreme lower temperatures. It must undergo a 720 hour weatherometer and a -40C cold chamber conditioning; over twice the requirements for USE-2."
An interesting point is the fact that the PV wire can sustain higher voltages and therfore is more beneficial in an ungrounded PV system. This is a point I am concerned with since my system is an ungrounded PV system.
- Location
- Illinois
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- retired electrician
Bob,
What about 690.31(B)?
What about 690.31(B)?
jaggedben
Senior Member
- Location
- Northern California
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- Solar and Energy Storage Installer
For ungrounded systems the code requires PV Wire. 690.35(D)(3)
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- Location
- Illinois
- Occupation
- retired electrician
Not exactly. That is one of 3 wiring methods permitted. It does not require the use of listed PV conductors, it permits them along with nonmetallic jacketed multiconductor cables and conductors in raceways.
I agree that there are (3) wiring methods permitted in this section. I was not planning on using a raceway for these cables but rather using wire clips. My interpertation here would be that if using a raceway you are free to use a conventional type cable but if not you must use either a non-metallic jacketed multiconductor cable or a cable listed and identified as a PV wire where installed and exposed as a single conductor. Does the USE-2 wire meet either of these (2) requiremnts? USE does show up in 310.13(2008)
Why is it that I typically see USE-2 chosen as a popular choice for PV cables as opposed to other conductors that may be sunlight resistant and rated for wet locations?
So if the module conductors are routed in an raceway does that mean they can technically be of THHN type?
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
If you can tell me how it is possible to connect a string of panels on an array to an inverter using only jacketed multiconductor cables and conductors in raceways, I'll admit that PV wire is not 'exactly' required. As far as I can see, PV wire with a crimped on solar connector (e.g. MC4, Tyco, etc.) is the only thing that you'll be able to use to directly connect to existing panel products. (On grounded systems, also USE-2.) From there you can take it a very short distance to a J-Box and transition to something else, if you wish, and do this for each home run. But if you've got the PV wire I don't know why you'd do that.
I'd say it's because 690.31(B) explicitly permits it, nothing else besides PV wire is explicitly permitted for solar in the code, and PV wire is more expensive.
Strictly speaking, for wet locations (i.e. on the roof) you need THWN or THHW or something else marked with a W. (see 310.10 (C)). But most wire marked for THHN these days is marked for THWN as well. (Again, though, you'll need some PV wire to get from the module to the J-Box at the start of the raceway.)
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